Motor Control

115 116 Control and Automation Solutions Guide Overview

Introduction Motor control design for industrial industries. Furthermore, electric motors savings will soon offset those initial applications requires attention consume about 45% of the world’s expenses. The return-on-investment to both superior performance electricity according to the International calculations are often straightforward. and ruggedness. Maxim’s feature Energy Agency (IEA) report of May Interfacing to the Motor integration and superior specifications 2011 on global energy consumption enhance motor controller equipment by driven systems. By Controller precision while improving robustness comparison, lighting is a distant second A very important aspect of every in harsh industrial environments. consuming 19%. With the cost of energy motor controller in the industrial rising steadily, plant operators look for control and automation setting is the Motor controllers either control variable ways to reduce energy consumption communications interface between power supplies to the motor or to while maintaining throughput. the factory control system and the electronic switches between the power Furthermore, with the availability of individual motor controller. All the supply and the motor. These switches reasonably priced and highly capable block diagrams in the individual motor are precisely timed to open and close to motor controllers for all types of motors, controller sections show a control panel make the motor rotate most effectively. plant engineers are free to choose motor that provides a direct user interface The timing is often governed by complex types that are less expensive, more at the controller and a standard mathematical equations based on motor efficient, and require less maintenance. separately wired communications architecture and electromagnetic theory. interface that connects to the fieldbus. Depending on the application, a motor To put the energy savings opportunity The fieldbus ultimately runs back to a controller can be as simple as a variable- in perspective, compare motor power PLC (programmable logic controller) generator, a pulsed-DC voltage consumption vs. speed when driving that sends commands to the motor source, or a complex signal generator fans and centrifugal pumps. The torque controller such as motor start, motor requiring sophisticated digital signal needed rises with speed, resulting in acceleration, speed adjustment, motor processing algorithms to generate the power draw that is proportional to stop, etc. An additional option exists: correct timing. For large motors, those in the cube of the speed! In other words, powerline communications (PLC, not to the multihorsepower range with multiple reducing the speed to one-half of full be confused with programmable logic power phases, precise control is essential. speed drops the power to one-eighth controller). This technology gives the At a minimum, the wrong timing can of full power. Even dropping the speed option of sharing command and control result in extreme power use. In the to 75% of full speed drops the power connections with power connections worst case, wrong timing can destroy consumption to 42% of full power (0.75 between the PLC (programmable logic the motor and the installation itself. cubed = 0.42). It is clear that significant controller) and the motor controller. savings in energy use can be realized Many electric motors have maximum by even small reductions in speed. This Motor Types torque at zero RPM, so these large fact, in turn, justifies the use of VFDs in Brushed DC Motors (BDCs) motors must be soft-started. To reduce applications that can tolerate the speed maintenance to a minimum, the Brushed DC (BDC) motors are among reduction. Of course, speed reduction mechanical mechanisms (clutches) the first motor types put to practical equates to performing the work more that traditionally provided this soft- use and they are still popular where low slowly, which, in some cases, directly start capability are rapidly being initial cost is required. These motors impacts throughput. Nonetheless, replaced by electronic soft-starters or have a wound and either there are numerous applications where variable frequency drives (VFDs). In a permanent or field motors do not need to run at full speed some applications motors must supply wound stator. Brushes slide across the to accomplish the work quickly enough. both forward and reverse tension to segments of the on the Pumping out a tank of fluid may not the load; optimally, braking energy rotor to switch the DC power source to need to be done as fast as possible. from overhauling loads is fed back the appropriate windings on the rotor. Venting a room may need a full-speed into the AC line using regenerative at first, but once the air is moving a BDC motors have their place for two VFDs instead of being wasted as heat slower speed may suffice. The EIA report important reasons: low initial cost and in large braking resistors or in high- (May 2011) states that it is feasible and ruggedness, because no electronics are maintenance mechanical brakes. cost effective to save 20% to 30% of total needed inside the motor. Because the Motor control is a very significant portion motor power consumption worldwide. motors suffer from wear of the brushes, of the Control and Automation market. springs, and commutators, they Certainly adding variable-speed According to U.S. Department of Energy, require high maintenance in intensive- controllers adds cost to the installation; motor driven equipment accounts for use applications. Sparking also occurs however, the forecasted energy 64% of the electricity consumed by U.S. between the brushes and the commutator

Motor Control 117 as a part of normal motor operation. Controllers for BDC Motors designers are abandoning linear voltage This, in turn, creates EMI/RFI and small The only variable available to control regulation because of its inherently amounts of ozone. Where system cost the speed of a BDC motor is the supply low efficiency. One way to realize a is a priority, BDC motors are a low- voltage. The voltage can be varied variable-voltage power supply from cost solution. While their efficiency or a fixed voltage can be pulsed with any switch-mode voltage regulator is to is generally lower than brushless variable duty cycle. For high efficiency inject or extract current into or out of DC (BLDC) motors, they approach in a variable voltage approach, a switch- its feedback node using a current sink/ equality under high-load conditions. mode power supply is required. Most source DAC. See Figure 1. When the

VDC VARIABLE VOLTAGE TECHNIQUE

CONTROL PANEL VCC VDC BUCK BUCK START

STOP SHDN FB VCC

CURRENT- MOTOR SENSE AMP FASTER SWITCH IOUT DEBOUNCER DAC

MOTOR TEMPERATURE SLOWER ADC SPEED, SENSOR POSITION µP SENSOR SENSOR INTERFACE VCC

DISPLAY DISPLAY SUPERVISOR DRIVER UART ISOLATION TRANSCEIVER

FIELDBUS VDC PWM TECHNIQUE

CONTROL PANEL VCC BUCK START

VDC STOP VCC TEMPERATURE SENSOR

MOTORMOTOR FASTER SWITCH GATE DEBOUNCER DRIVER

SLOWER MOTOR SPEED, SENSOR POSITION µP INTERFACE SENSOR

VCC OP AMP ADC DISPLAY DISPLAY SUPERVISOR DRIVER

UART ISOLATION TRANSCEIVER

FIELDBUS

Figure 1. Two control techniques for BDC motors. The upper diagram shows a variable voltage technique that is high efficiency due to the switching power supply. The lower diagram shows the PWM technique that can be lower cost if the motor is rated for the full supply voltage.

118 Control and Automation Solutions Guide user adjusts the speed control or when speed signal (usually a pulse frequency rotating part through a commutator. The the microcontroller receives a command proportional to the motor rotation rate) brushes and mechanical commutator are through the electronic interface, the must be fed into a controller that will replaced by electronic commutation of microcontroller then instructs the current respond by either adjusting the motor the stator windings. This increases motor sink/source DAC (e.g., DS4432) to change voltage or the PWM duty cycle. With life significantly. The initial cost of a BLDC its output current value. This forces the sufficient switching frequency, the motor is higher than an equivalent BDC regulator to change the output voltage of the motor windings act motor, although the cost of permanent to the motor up or down, respectively, to as a lowpass filter that keeps the motor has decreased significantly over keep the feedback pin’s voltage constant. current close to constant with only minor the past years. With precise commutation ripple, thus producing low torque ripple. and rotor position sensing, efficiency is Alternatively, if the motor can handle generally higher than equivalent BDC the high-DC voltage, one can convert To reverse the direction of the BDC motors. They also produce more torque the input control to a pulse-width- motor, current must flow through the per unit weight. Another significant modulated (PWM) duty cycle applied motor in the opposite direction. This advantage for industrial applications is to a power switch between the power can be accomplished using power that since there are no brushes, there are supply and the motor. By varying the MOSFETs or IGBTs in an H-bridge no sparks generated, so the BLDC motors duty cycle, the average power to the configuration Figure( 2). These MOSFETs can be used in explosive environments. motor is adjusted, as is its output power can be either voltage controlled or and speed. If constant speed is needed PWM controlled for speed control. Due to their higher efficiency over under a varying load, then motor Brushless DC (BLDC) Motors a wide range of speeds and loads, speed detection is needed. This motor BLDC motors are seeing wider use in A BLDC motor spins the magnets heating, ventilation, air conditioning, instead of the windings—the inverse of VDC and refrigeration (HVAC&R) systems. a BDC motor. This has advantages and disadvantages. A BLDC motor has neither Q1 Q2 commutator nor brushes, so it requires less maintenance than a BDC motor. The BLDC motor’s rotor can take different MOTOR forms, but all are permanent magnets. The armature is fixed and holds the stator Q3 Q4 windings; the rotor carries the magnets and can either be an “inrunner” or an “outrunner.” Inrunners have the rotor inside the stator and outrunners have the rotor outside the stator (Figure 3). Figure 3. Disassembled outrunner BLDC motor. Fixed armature Figure 2. H-bridge for driving a BDC motor in both directions. Either approach eliminates the problem carries the stator windings. The rotor carries the permanent When Q1 and Q4 are on, the motor moves one direction. When of connecting the power source to a magnets. Q2 and Q3 are on, the motor moves in the opposite direction.

Motor Control 119 Controllers for BLDC Motors Stepper Motors occurs between adjacent windings to Since the commutation in a BLDC motor Stepper motors are really more like provide smaller steps. Microstepping is (Figure 4) is electronic, some means is rotary positioners than motors. They are achieved with sinusoidal, overlapping required for detecting rotor position usually smaller motors with many poles current waveforms that give very relative to the stationary armature. used for precise positioning applications smooth and quiet rotation. Typical solutions for this are Hall-effect (Figure 5). They are often driven “open sensors and rotary encoders such as loop,” meaning there is no position optical encoders, resolvers, or rotary detection. Their position is assumed to variable differential transformers (RVDTs). follow the step commands exactly. Loss More designs are using sensorless of step position can occur, however, so approaches where stator coil back EMF some mechanism must be provided to variation is sensed, which indicates indicate slippage and to reset proper rotor position. This information is positioning. At low drive rates, they typically sent to a microprocessor to come to a complete stop between each determine power FET drive timing. step. Many drive waveforms are possible, Various user interfaces allow soft- the simplest has each winding energized starting, acceleration control, speed one at a time. Other variations are Figure 5. (windings removed) showing multi- control, and response to locked rotor. possible where overlap in energization toothed rotor and stator design for fine stepping.

VDC MOSFET H-BRIDGE

BRUSHLESS DC MOTOR VCC BUCK

CURRENT-SENSE MOTOR AMP x3 SPEED, TEMPERATURE POSITION SENSOR SENSOR VCC VCC

SUPERVISOR RESET HALF-BRIDGE DRIVER FIELDBUS

µP HALF-BRIDGE TRANSCEIVER ISOLATION UART DRIVER

I/0 HALF-BRIDGE SENSOR FRONT PANEL DRIVER INTERFACE I/0 DISPLAY DISPLAY DRIVER

SWITCH SWITCHES ADCs DEBOUNCER

KEYBOARD OP AMP SCANNER KEYBOARD

Figure 4. Controller for BLDC motor.

120 Control and Automation Solutions Guide Controllers for Stepper Motors for a particular step position. The the rotor is made of only ferromagnetic Stepper motors are constant power additional electronics to sense winding material and has no windings. It is a motors if driven with a constant supply currents and to control the switching very reliable, low-maintenance motor voltage. As speed increases, torque adds some cost and complexity, but with high power density at low cost, decreases. This happens because of it allows stepper motors to be driven all of which come at the expense of the limitation on current ramp rates in with high torque at high speed. more complex electronic controls. the windings due to their inductance. Microprocessors are commonly Opposing stator poles are energized in Maximum torque is realized at zero incorporated in stepper motor drivers sequence and the rotor poles closest speed. So to increase torque at higher to provide the controls needed. to the energized stator poles become speeds, high-voltage drivers with Sophisticated control capability is magnetized and are attracted to them, current limiting are sometimes used common for stepper motors since they reducing magnetic reluctance when (Figure 6). These are called “chopper are often employed in machines that brought into alignment. Before full drives,” and are designed to generate require fast precision movements, such alignment is achieved, the next phase a nearly constant current in each as in robotics. Acceleration/deceleration is energized to keep the motor turning. winding rather than simply switching a profiles, holding torque, and other There is no need for any transfer of constant voltage. On each step, a very parameters are often provided for. electrical power to the rotor so there are high voltage is applied to the winding. Switched Reluctance Motors (SRMs) no brushes, commutators, or slip rings. When the current limit is reached, the With electrical commutation there are Switched reluctance motors (SRMs) voltage is turned off or “chopped.” At no sparks so these motors can be used are a form of stepper motor, but are this point the winding current starts in explosive environments. They are also usually much larger and have fewer ramping down to a lower limit where good for holding a load in a stationary poles than the traditional stepper the voltage is again turned on, keeping position for long periods of time. the winding current relatively constant motor. The key to these motors is that

VDC

VDC V VCC CC BUCK V DC SUPERVISOR

STEPPER BOOST MOTOR V SHDN CC

GATE DRIVER TEMPERATURE SENSOR GATE FRONT PANEL DRIVER

DISPLAY DISPLAY DRIVER µP

SWITCH SWITCHES DEBOUNCER ADC

KEYBOARD OP AMP SCANNER KEYBOARD

UART ISOLATION TRANSCEIVER

FIELDBUS

Figure 6. Controller for stepper motor. The boost regulator and the current sense per phase allow current to ramp quickly in each pole of the motor. Motor response is fast. When the maximum current per phase is reached, the boost regulator is shut down until the minimum current per phase is reached again. The cycle is repeated until the next step is made.

Motor Control 121 Controllers for SRMs allows each phase of a 3-phase motor relatively constant, ramping down only SRMs are similar to stepper motors to be energized by the top FET and the very slowly with the bottom diode because they need power switched to the appropriate bottom FET, which are both closing the loop around the winding. proper windings at the appropriate times. turned on simultaneously (Figure 8). The Then to discharge the phase quickly in The most common configuration is similar current is allowed to ramp up to a limit, preparation for the next step, the bottom to an H-bridge, but differs somewhat. The at which point the top FET is turned off. FET is also turned off. The voltage across driver is called an N+1 switch and diode This is the freewheeling mode, where the the winding is now clamped to the asymmetric bridge converter (Figure 7). It winding inductance keeps the current opposite polarity by the top and bottom diodes. This causes the current to ramp V down at about the same rate that it ramped up, except for the effect of two 1 additional diode drops making it ramp 3 2 down slightly faster. This configuration allows each phase to be switched on 1 2 3 and off quickly, especially with a high- 2 3 voltage supply, allowing for high-speed motor operation at high torque. Figure 8 1 shows only a single current-sense amp sensing the current on the high-side FET. 0 This is only adequate for simple control systems. Complete control also requires Figure 7. “N+1 switch and diode” asymmetric bridge for driving SRMs. The control circuitry needed for the IGBTs shown is current sensing on each low-side FET. shown in Figure 8.

325V DC OR 650V DC

SWITCHED

AC MAINS (3-PHASE) 230V AC OR 460V AC

VR OR HALL-EFFECT TEMPERATURE SENSOR SENSOR

AC-DC DC-DC CONVERTER CONVERTER

VOLTAGE RESET HIGH-SIDE SUPERVISOR GATE DRIVER FIELDBUS SENSOR INTERFACE TRANSCEIVER ISOLATION UART µP LOW-SIDE GATE DRIVERS

FRONT PANEL I/0 I/0 DISPLAY CURRENT-SENSE AMP DISPLAY DRIVER ADC SWITCH SWITCHES DEBOUNCER

KEYBOARD SCANNER KEYBOARD

Figure 8. Controller for a switched reluctance motor.

122 Control and Automation Solutions Guide AC the secondary winding (rotor) carries frequency and voltage, respectively. The AC induction motor (Figure 9) the induced secondary current creating If constant speed is needed, VFDs is the workhorse motor for many a magnetic field. Torque is produced as can use position- or speed-detection industrial applications such as those the rotor field tries to align itself with feedback to increase the drive frequency for driving pumps, blowers, conveyors, the applied rotating stator field. No as needed to keep the motor speed cranes, etc. It is one of the simplest and slip rings or commutators are needed constant under varying loads. most reliable motor designs and can since no source power is physically Controllers for AC Induction Motors connected to the rotor. The most range in size from a few watts to many AC induction motors operate with common designs have three stator kilowatts. The induction motor is an the least torque ripple when the windings and are driven from 3-phase asynchronous motor and is basically an phase current is sinusoidal. Due to the AC sources. Although direct connection AC transformer with a rotating shorted inductance of the windings, the phase to AC mains is therefore possible, in secondary. The primary winding (stator) can be PWM driven from a fixed DC most applications, induction motors is connected to the power source and supply to achieve this current waveform. require some form of soft- or VFD. The two most common approaches to Induction motors “slip” under load. The induction include “vector amount of slip is directly proportional control” and “.” to the torque required to drive the load. These techniques are beyond the scope Under no-load conditions, no torque of this document, but information is produced and the rotational speed is readily available. Suffice it to say is almost exactly the driving frequency that to fully implement these control divided by the number of poles in the techniques, a fairly powerful processor stator. These motors are easily speed and or DSP is required, but the benefits are torque controlled by varying the drive many. The result is a VFD (Figure 10) Figure 9. An AC induction motor.

325V DC OR 650V DC IGBT H-BRIDGE AC INDUCTION MOTOR

ANALOG VOLTAGE/ AC MAINS (3-PHASE) CURRENT SENSORS 230V AC OR 460V AC

VR OR HALL-EFFECT SENSOR TEMPERATURE SENSOR AC-DC DC-DC CONVERTER CONVERTER

VOLTAGE HIGH-SIDE SUPERVISOR RESET FIELDBUS GATE DRIVERS

TRANSCEIVER ISOLATION UART µP LOW-SIDE GATE DRIVERS FRONT PANEL I/0 I/0 DISPLAY CURRENT-SENSE AMPS DISPLAY DRIVER SENSOR ADC INTERFACE SWITCH SWITCHES DEBOUNCER ADC

KEYBOARD SCANNER ADC KEYBOARD

VOLTAGE-SENSE AMPS

ADC

ADC

ADC Figure 10. Variable frequency drive for an AC induction motor.

Motor Control 123 that provides complete control Controllers for AC Synchronous Motors If the rotor uses DC excitation, its voltage capability over motor soft-starting, Various control methods exist for AC can vary with a high-efficiency switching acceleration, torque, speed maintenance, synchronous motors. The motors’ power supply and voltage control. deceleration, and holding torque. stator windings can be driven with Linear Motors Synchronous Motors variable-frequency AC signals from a Linear motors are effectively motors that A runs VFD, thereby providing soft-starting have been unrolled and laid out flat. synchronously with the AC excitation and exacting speed control. If a low The moving part is usually called the it receives. Various configurations are frequency is not first applied to a forcer and is connected to the external possible. One approach applies the stopped synchronous motor, it will not power source while the rails are lined AC line to the stator windings around self-start. It must be given a chance with permanent magnets. The opposite the frame while a DC excitation is to “pull in” to synchronization. Some configuration is also used. Everything applied through slip rings to the synchronous motors allow the rotor from maglev trains (Figure 11) to rail rotor. In many synchronous motors windings to be shorted, temporarily guns are based on this principle. Very the rotor has permanent magnets converting it to an induction motor precise machine positioning systems instead of DC-excited windings. High- while it starts. Then once it is close use these motors for cutting large speed synchronous motors are used in to synchronous speed, the short is objects with high accuracy. Linear machining applications where the cutter opened and it becomes synchronous. motors include linear induction motors speed must be maintained at precisely (LIMs) and linear synchronous motors fixed rates or the machined-surface (LSMs). Controllers for linear motors finish will show signs of speed variation. are quite varied due to the wide range of applications for them. Nonetheless, When driven mechanically, they share similarities with VFDs. synchronous motors will produce electricity, becoming . They are used extensively in power plants to generate grid power. DC-excited synchronous motors can also be used in power plants and large factories to correct the power factor by being run under no load in parallel with the large loads. As the DC excitation of the rotor is modified, it produces either a leading or lagging power factor to cancel the nonunity power factor Figure 11. Maglev train driven by a . of the load. In this application they are called synchronous condensers.

124 Control and Automation Solutions Guide Featured Products

Sink/Source Current DAC Adjusts Power- Benefits Supply Output Voltage to Vary Supply to • Simplicity of DC motor speed control Motors via digital interface • Easy design reuse due to highly DS4432 scalable outputs • Dual outputs with individual range The DS4432 contains two I2C programmable current DACs that are each capable of settings provide course and fine sinking and sourcing current up to 200µA. Each DAC output has 127 sink and 127 motor speed control source settings that are programmable using the I2C interface. The current DAC outputs power up in a high-impedance state. Full-scale range for each DAC is set by external resistors providing highly scalable outputs. Fine and course granularity can be achieved by combining the two outputs when set for different ranges.

VCC SUPPLY TO MOTOR

4.7kΩ 4.7kΩ VCC OUT

SDA DC-DC R0A SCL CONVERTER DS4432 OUT0 FB OUT0 GND R0B

FS0 FS0

RFS0 RFS1

Typical operating circuit of the DS4432.

Motor Control: Featured Products 125 Precise Current Measurements Ensure Better Benefits Motor Control • Provide reliable operation in harsh motor control environments MAX9918/MAX9919/MAX9920 ◦◦ 400µV (max) input offset voltage (VOS) The MAX9918/MAX9919/MAX9920 are current-sense amplifiers with a -20V to +75V ◦◦ -20V to +75V common-mode input range. The devices provide unidirectional/bidirectional current sensing in very voltage range provides reliability for harsh environments where the input common-mode range can become negative. measuring the current of inductive Uni/bidirectional current sensing measures charge and discharge current in a system. loads The single-supply operation shortens the design time and reduces the cost ◦◦ -40°C to +125°C automotive of the overall system. temperature range • Integrated functionality reduces system cost and shortens design cycle ◦◦ Uni/bidirectional current sensing ◦◦ Single-supply operation (4.5V to 5.5V) eliminates the need for a second supply ◦◦ 400µV (max) input offset voltage (VOS) ◦◦ 0.6% (max) gain accuracy error

VCC VCC VBATT

OUT φ1A φ2B MAX9918 A ADC RSENSE M MAX9920 R2 RS+ FB μC

INPUT-STAGE LEVEL SHIFTER R1 RS- REFIN REF ADJUSTABLE GAIN φ2B φ1B GND SHDN GND

The MAX9918/MAX9920 current-sense amplifiers provide precise uni/bidirectional current sensing in very harsh environments.

126 Control and Automation Solutions Guide Highly Accurate, Reliable Monitoring of Motor Benefits Speed and Position with a Sensor Interface • Integrated functionality eases motor control design, reduces system cost MAX9621 ◦◦ Select the analog or digital output to monitor the Hall-effect sensor’s The MAX9621 is a dual, 2-wire Hall-effect sensor interface with analog and digital condition outputs. This device enables a microprocessor to monitor the status of two Hall- ◦◦ High-side current-sense architecture effect sensors, either through the analog output by mirroring the sensor current for eliminates the need for a ground- linear information, or through the filtered digital output. The input current threshold return wire and saves 50% of the can be adjusted to the magnetic field. The MAX9621 provides a supply current wiring cost to two 2-wire Hall-effect sensors and operates in the 5.5V to 18V voltage range. The high-side current-sense architecture eliminates the need for a ground-return • Reliable operation in a harsh wire without introducing ground shift. This feature saves 50% of the wiring cost. environment ◦◦ Protects against up to 60V supply voltage transients ◦◦ Detects a short-to-ground fault condition to protect the system

0.1μF 1.8V TO 5.5V BATTERY: 5.5V TO 18V OPERATING, RPU RPU 60V WITHSTAND 10kΩ 10kΩ RSET BAT ISET REF REFERENCE

SLEEP-MODE SLEEP CONTROL BAT 100kΩ

AOUT1 ADC

5kΩ

DOUT1

FILTER IN1 REF N 0.01μF MICROPROCESSOR

S ECUCONNECTOR

BAT INPUT REMOTE SHORT GROUND DETECTION MAX9621

AOUT2 ADC

5kΩ IN2 N DOUT2 0.01μF S

FILTER REF

REMOTE GROUND GND

Functional diagram of the MAX9621 Hall-effect sensor interface.

Motor Control: Featured Products 127 Improve Performance and Reliability in Benefits Motor Applications with a Differential VR • High integration provides accurate phase information for precise sensing Sensor Interface of rotor position MAX9924–MAX9927 ◦◦ Differential input stage provides enhanced noise immunity The MAX9924–MAX9927 VR, or magnetic coil, sensor interface devices are ideal ◦◦ Precision amplifier and comparator for sensing the position and speed of motor shafts, camshafts, transmission allow small-signal detection shafts, and other rotating wheel shafts. These devices integrate a precision ◦◦ Zero-crossing detection provides amplifier and comparator with selectable adaptive peak threshold and zero- accurate phase information crossing circuit blocks that generate robust output pulses, even in the presence of substantial system noise or extremely weak VR signals. The MAX9924– MAX9927 interface to both single-ended and differential-ended VR sensors.

MOTOR BLOCK MAX9924 DIFFERENTIAL VR SENSOR AMPLIFIER

μC ADAPTIVE/MINIMUM AND ZERO-CROSSING THRESHOLDS

INTERNAL/EXTERNAL BIAS VOLTAGE

Simplified block diagram of the MAX9924 VR sensor interface to a motor.

128 Control and Automation Solutions Guide Resolve Very Fine Motor Adjustments and Benefits Operate Higher Accuracy Systems with • Industry-leading dynamic range allows early detection of error signals Simultaneous-Sampling ADCs ◦◦ 93dB SNR and -105dB THD MAX11044/MAX11045/MAX11046 • Simultaneous sampling eliminates MAX11047/MAX11048/MAX11049 phase-adjust firmware requirements ◦◦ 8-, 6-, or 4-channel ADC options The MAX11044–MAX11049 ADCs are an ideal fit for motor control applications ◦◦ Lower system cost by as much as that require a wide dynamic range. With a 93dB signal-to-noise ratio (SNR), these 15% over competing simultaneous- ADCs detect very fine changes to motor currents and , which enables a sampling ADCs more precise reading of motor performance over time. The MAX11044/MAX11045/ ◦◦ High-impedance input saves costly MAX11046 simultaneously sample four, six, or eight analog inputs, respectively. All precision op amp ADCs operate from a single 5V supply. The MAX11044–MAX11046 ADCs measure ◦◦ Bipolar input eliminates level shifter ±5V analog inputs, and the MAX11047–MAX11049 measure 0 to 5V. These ADCs also ◦◦ Single 5V voltage supply include analog input clamps that eliminate an external buffer on each channel. ◦◦ 20mA surge protection • Eliminate external protection components, saving space and cost ◦◦ Integrated analog-input clamps and small 8mm x 8mm TQFN package provide the highest density per DSP-BASED DIGITAL channel PROCESSING ENGINE MAX11046

16-BIT ADC IGBT CURRENT DRIVERS 16-BIT ADC

16-BIT ADC

16-BIT ADC

16-BIT ADC

IPHASE1

IPHASE3

IPHASE2

THREE-PHASE ELECTRIC MOTOR

POSITION ENCODER

The MAX11046 ADC simultaneously samples up to 8 analog-input channels.

Motor Control: Featured Products 129 Recommended Solutions

Part Description Features Benefits AC-DC and DC-DC Converters and Controllers MAX17499/500 Isolated/nonisolated current-mode 85V AC to 265V AC universal offline Primary-side regulation eliminates PWM controllers ideal for flyback/ input voltage range (MAX17500), optocouplers, allowing low-cost forward topologies 9.5V DC to 24V DC input voltage isolated supplies. range (MAX17499), programmable switching frequency up to 625kHz, 1.5% reference accuracy MAX5069 Isolated/nonisolated current 85V AC to 265V AC universal Minimizes footprint due to wide mode PWM controller with dual offline input voltage range range programmable switching FET drivers ideal for push-pull and (MAX5069A/B), 10.8V DC to frequency; programmable half/full-bridge power supplies 24V DC input voltage range UVLO/hysteresis ensures proper (MAX5069C/D), programmable operation during brownout switching frequency up to 2.5MHz, conditions. programmable UVLO and UVLO hysteresis MAX15062* High-voltage synchronous, micro 4V to 36V input voltage range, Reduces total solution size and buck regulator fixed 700kHz switching frequency, cost with high integration and integrated high-side and low-side small package. FETs, internal compensation ADCs MAX11044/45/46 16-bit, 4-/6-/8-channel, 93dB SNR: -105dB THD; 0 to 5V High-impedance input saves MAX11047/48/49 simultaneous-sampling SAR ADCs or ±5V inputs; parallel interface the cost and space of external outputs, all eight data results in amplifier. 250ksps; high-input impedance (> 1MΩ) MAX1377/MAX1379/MAX1383 12-bit, dual, 1.25Msps, 0 to 5V, 0 to 10V, or ±10V inputs: Serial interface saves cost and simultaneous-sampling SAR ADCs 70dB SNR; SPI interface space on digital isolators. MAX11040K 24-bit, 4-channel, simultaneous- 117dB SNR, 64ksps, internal Reduces motor control firmware sampling, sigma-delta ADC reference, SPI interface, 38-pin complexity. TSSOP package MAX11203 16-bit single-channel, ultra-low- Programmable gain, GPIO, high Eases achieving high-efficiency power, delta-sigma ADC resolution per unit power ratio designs. DACs DS4432 Dual sink/source current DAC 50µA to 200µA sink/source range, Provides simple and precise digital with sink and source settings 127 sink, 127 source settings speed control for a wide range of programmable via I2C interface; DC motor control applications. range settable with resistors Current-Sense Amplifiers MAX34406 Quad current-sense amplifier with Unidirectional current sensing; Wide dynamic range supports overcurrent threshold comparators fixed gains of 25, 50, 100, and wide range of motor current- 200V/V; ±0.6% gain error; 2V to sensing applications. 28V common-mode range MAX9918/19/20 -20V to +75V input range; uni/ 0.6% max gain error, 120kHz -3dB Wide dynamic range and high bidirectional current-sense BW, -40°C to +125°C operating accuracy supports wide range of amplifiers temperature range motor current-sensing applications. MAX9643 High-speed current-sense 15MHz bandwidth, -1.5V to +60V Provides very fast response to amplifier input range, 50µV max VOS, -40°C to quickly changing currents in motor +125°C operating temperature range control applications. (Continued on following page)

*Future product—contact the factory for availability.

130 Control and Automation Solutions Guide Part Description Features Benefits Operational Amplifiers

MAX9617/18/19/20 High efficiency, zero drift, op amps 10µV (max) VOS over time and Allow sensing low-side motor with low noise and RRIO temperature range of -40°C to current with high accuracy at low +125°C, 59µA supply current, power consumption. 1.5MHz GBW, SC70 package MAX9943/44 38V precision, single and dual op Wide 6V to 38V supply range, low Wide operating voltage range amps 100µV (max) input offset voltage, and precision performance under drives 1nF loads most capacitive loads provide signal processing in wide range of applications. Hall-Effect Sensor Interface MAX9621 Dual, 2-wire Hall-effect sensor Analog and filtered digital Integration eases motor control interface outputs, high-side current sense, design. 60V capability, detects short to ground fault Temperature Sensors MAX31723 Digital thermostat with SPI/3-wire No external components, -55°C Eases processor burden by storing interface to +125°C measurement range, temperature thresholds internally ±0.5°C accuracy, configurable in nonvolatile memory. 9- to 12-bit resolution, nonvolatile thermostat thresholds MAX31855 Thermocouple-to-digital converter Cold-junction compensated; works Simplifies system design while with K, J, N, T, or E types; 14-bit, SPI providing flexibility for various interface; -270°C to +1800°C thermocouple types. Variable Reluctance (VR) Sensor Interface MAX9924–MAX9927 Reluctance (VR or magnetic coil) Integrated precision amplifier Improve performance by sensor interfaces and comparator for small-signal accurately detecting position and detection, flexible threshold speed of motors and rotating options, differential input stage, shafts. zero-crossing detection MOSFET Drivers MAX15012 Half-bridge gate driver for high- UVLO, fast (35ns typ) and matched Prevents MOSFET damage due to and low-side MOSFETs with 2A (8ns max) propagation delays, supply brownout; allows higher peak source/sink current drive 175V high-side MOSFET voltage frequency switching applications; capability allows use in high voltage applications. MAX15024 Low-side, 4A MOSFET drivers Single/dual operation, 16ns Shrinks designs with small propagation delay, high sink/ package and allows fast switching source current, 1.9W thermally with tightly matched propagation enhanced TDFN package delays. (Continued on following page)

Motor Control: Recommended Solutions 131 Part Description Features Benefits Interface Transceivers MAX13448E Fault-protected RS-485 transceiver ±80V fault protected, full-duplex Makes equipment more robust operation, 3V to 5.5V operation and tolerant of misconnection faults. MAX14840E High-speed RS-485 transceiver 40Mbps data rates, ±35kV (HBM) High receiver sensitivity and ESD tolerance, 3.3V, +125°C hysteresis extend cable lengths in operating temperature, small 3mm harsh motor control environments. x 3mm TQFN package MAX14770E PROFIBUS transceiver ±35kV (HBM) ESD protection, Industry’s highest ESD protection -40°C to +125°C temperature makes motor control more robust. range, small 3mm x 3mm TQFN package MAX13171E/3E/5E Multiprotocol data interface Complete RS-232 and related Enable flexible interfaces with pin- chipset protocols equipment interface selectable protocols. solution, up to 40Mbps, true fail-safe receivers, ±15kV ESD protection MAX13051 CAN transceiver ±80V fault protection, autobaud, Provides robust industrial strength ISO 11898 compatible, up to CAN interface solution. 1Mbps, -40°C to +125°C operation Voltage Supervisors MAX16052/3 High-voltage supervisor Adjustable voltage thresholds and Ease supervisory designs for timeout; VCC to 16V and open- industrial applications with high- drain output to 28V voltage capability. MAX6495 72V overvoltage protector Protects against transients up to Increases system reliability by 72V, small 6-pin TDFN-EP package preventing component damage from high-voltage transients. Control Interfaces MAX6816/17/18 Single, dual, octal switch ±15kV ESD (HBM) protection Assure high reliability, clean debouncer pushbutton signal from motor control panels. MAX7370 Key-switch controller plus LED Up to 64-key, separate press/ Enables high reliability keyboard backlight drive with dimming release codes, ±14kV Air Gap ESD, scanning and display illumination LED drive with PWM dimming in one IC. control and blink, optional GPIO MAX16054 Pushbutton on/off controller with Handles ±25V input levels, Enables simple, robust control debounce and ESD protection ±15kV ESD, deterministic output panel interface in small SOT23 on power-up, no external package. components MAX6971 16-port, 36V constant current LED 25Mb 4-wire serial interface, Eases design of robust control driver up to 55mA current per output, panel indicators. fault detection, high dissipation package, -40°C to +125°C operation UARTs MAX3108 Serial UART, SPI, I2C compatible 24Mbps (max) data rate, 128- Reduces host controller word FIFOs, automatic RS-485 performance requirements and transceiver control, 4 GPIOs, 24-pin cost. SSOP or small 3.5mm x 3.5mm TQFN packages

132 Control and Automation Solutions Guide Calibration and Automated Calibration

133 134 Control and Automation Solutions Guide The goal of calibration is to maintain a goods must either design with piece of equipment in its most accurate Calibration high-precision components or state. The goal of automated calibration Calibration usually addresses accuracy use some form of calibration. is to improve efficiency and consistency and less often precision. From the above All electronic products must pass at of the calibration process, while discussion it is evident that calibration least minimal signal testing prior to minimizing the down time required may not have any effect on precision, shipping to ensure that the product to verify equipment performance. because other circuit parameters such as noise may have an influence on works out of the box. A rigorous Accuracy vs. Precision precision and no amount of calibration test and calibration process also reduces liability from performance The terms accuracy and precision are will reduce the spread of values. This is errors and provides a paper trail that often used synonymously, but they are of course not always the case, such as shows that industry and regulatory not the same thing. Both are, however, in light beam focusing. When a beam is requirements have been followed. needed to achieve the best results. We correctly focused, its spread is reduced. can illustrate the differences between This is, of course, not always the case. Although new products may meet these two terms through the following For complete basic calibration, it is often strenuous requirements for calibration, example. To measure the performance required to correct for both offset and due to the effects of use, wear, and of a particular system, one can plot the span (gain). This requires calibration environmental conditions, over results of a large number of samples over at more than one point. If a system is time products may no longer meet time on a graph and note the differences linear, calibration at two points will specifications. For some products the between the actual results and the suffice since two points define a line effect is easily seen: a cell phone that no desired result (Figure 1). Accuracy is the (Figure 2). If a system is nonlinear, longer receives calls, or a hard drive that measure of how close the mean of the more calibration points are needed. loses data. For others, e.g., a voltmeter total set of results is to the desired result. with a small drift, the effect cannot

Precision is a measure of the spread CALIBRATED: be easily seen, but the impact may be RESPONSE GAIN ERROR, NO OFFSET ERROR NO GAIN OR of these results relative to this mean. OFFSET ERROR costly. Or, in the case of an insulin pump, Precision only addresses how dispersed OFFSET ERROR, the impact may be even dangerous. For the results are, not how far they are NO GAIN ERROR many types of industrial (and medical) from the average of the desired value. electronic equipment, calibration is an on-going process and is the reason why many products are now being NUMBER OF OCCURRENCES designed with self-calibration circuitry. For control devices used in a production ACCURACY environment, a proper calibration process uses test equipment that has STIMULUS been certified to standards traceable to a government agency. In the U.S. this agency is the National Institute of Figure 2. For proper basic calibration, the system response to MEASURED Standards and Technology (NIST). This stimuli must be corrected for both offset and gain errors. Offset VALUES type of certified calibration requires PRECISION errors do not produce a zero output for a zero input. Gain errors (when no offset error remains) show more deviation from the the services of a certified metrology Figure 1. Accuracy and precision are two very different things. expected results at larger input stimuli. lab. The lab will not only calibrate the equipment based upon recognized standards, but will also provide reports Calibration is the process of adjusting as part of their service. These reports circuit parameters, such as offsets prove that the equipment has been and gains, to make equipment meet measured and adjusted relative to a specifications or a standard. All chain of standards traceable back to organizations producing electronic the government’s master standards.

Calibration and Automated Calibration 135 of thousands or even millions of devices Test Equipment Benefits of Automated are built and they do not receive the Calibration Calibration same level of testing for proper signal While calibration of the end product is Automated calibration can reduce cost levels, variances, and tolerance margins. required to establish its performance, in many areas. It does this by removing All practical components, both the production test equipment used manufacturing tolerances, allowing mechanical and electronic, have to calibrate it must, of course, also the use of less expensive components, manufacturing tolerances. The more be operating within its specifications reducing test time, improving reliability, relaxed the tolerance, the more (Figure 3). This calibration is maintained increasing customer satisfaction, affordable the component. When with more accurate test equipment reducing customer returns, lowering components are assembled into a and reference standards used only warranty costs, and increasing system, the individual tolerances occasionally for this purpose. Eventually the speed of product delivery. accumulate to create a total system these standards must also be calibrated. Automated Calibration error tolerance. When thousands As one moves further back in the chain, Characteristics of devices are manufactured, the the equipment gets more accurate and errors can multiply so that a properly Automated calibration is built around more sensitive, usually by an order of manufactured product may not work. circuitry that is designed into the end magnitude or at least 4:1 at each stage, If this happens enough to reduce equipment for the explicit purpose of so it must be treated with more care to yields, then profitability is affected. maintaining calibration. This circuitry avoid “knocking” it out of calibration. Through the proper design of trim, can take a variety of forms and adjustment, and calibration circuits, it Today test equipment is being built functions. For example, this circuitry is possible to correct for the worst-case with new techniques that reduce or could utilize digital communication tolerance stackups, thereby ensuring eliminate calibration expenses or between the end equipment and a that a higher percentage of products downtime. These techniques, called remote host or a factory test system. can be made to meet specifications electronic or automated calibration, use Once communication is established, upon exiting the assembly line. self-calibration or digital calibration. the end equipment uploads data to the host and then through commands Final-test calibration corrects for these and downloaded data, the host errors. Multiple adjustments may be calibrates the end equipment’s circuit required to calibrate the device under parameters. Or, the circuitry could be test (DUT) to meet specifications. completely internal to the equipment For example, suppose the design itself. In this latter case, the circuitry engineers find that they can use ±5% might measure an imbedded precision resistors and a low-cost op amp because component, such as a precision resistor their Monte Carlo testing shows that or voltage reference, to allow adjustment even under worst-case tolerance and verification of the accuracy of stackup, the use of two low-cost digital the signal chain components. potentiometers (pots) for offset and Testing and calibration generally gain can calibrate out all the variation fall into three broad areas: from the components chosen. They also 1. Production-line final-test calibration see that to eliminate the adjustability 2. Periodic self-testing altogether, they would have to use 3. Continuous monitoring and expensive tight tolerance resistors and a readjustment precision op amp. With this knowledge, they decide to use the circuits as-is Automated and electronic calibration and to simply adjust the offset and can be cost effective in each area. span (gain) during final test to meet Final-Test Calibration system specifications. By using digital Figure 3. An oscilloscope has many functions to be calibrated When a circuit is developed in the lab, pots instead of mechanical pots, they in the instrument and on the probe itself. Voltage probes typically 20 to 50 devices are prototyped avoid using human labor to make the usually have a compensation adjustment for proper frequency and tested. All signal levels are adjustments. response. A true square wave is generated by the scope to test measured, and variances and tolerance this probe setting. Internal self-tests and self-calibrations are Periodic Self-Testing margins are noted. However, when the common, but use of known good external standards is still Environmental influences in the field can product goes into production, hundreds periodically needed for calibration certification. create a need for test and calibration.

136 Control and Automation Solutions Guide Such environmental factors include occur only very rarely after system monitoring and subsequent control. temperature, humidity, vibration, maintenance which can be too costly Digital control of analog circuitry using contamination, and component aging. if system performance is suffering precision DACs and digital pots allows These factors are accounted for with a or safety margins are compromised economical remote-control processes, combination of self-test at power-up from an out of calibration component. while also ensuring the precision and periodic or continuous testing. Depending on the impact of a system needed to meet specifications. The field testing can be as simple as not being calibrated, these applications sensing temperature and compensating may need to use continuous monitoring Circuitry for Electronic accordingly, or it can be more complex. with subsequent readjustment. and Automated Good examples of applications that A simple example of power-up self- requires continuous monitoring and Calibration testing is to automatically briefly short calibration are a variety of safety Electronic calibration is based on the inputs of an amplifier together to systems in nuclear power plants. digitally controlled calibration devices: set a zero reading point (Figure 4). DACs with voltage or current outputs Doing so allows any changes to input Continuous calibration consists of can be used to provide temporary inputs offset voltage or to downstream circuit circuitry that self-corrects continuously to analog signal chains or to adjust parameters to be calibrated out. Another or very frequently. This can be bias levels. Digital pots with variable example is to electronically swap the accomplished in a variety of ways either resistances or variable resistance ratios resistive temperature sensor with a with techniques similar to periodic can provide gain and offset adjustments, precision fixed resistor to enable the self-testing, just done more frequently, analog switches can select different instrument to calibrate the temperature or with other techniques that allow the gain or filter corner setting components, reading to the expected value. Using two system to continue to operate. In the and potentially any other digital-to- different precision resistors can establish former case, very brief interruptions analog transducer such as a digitally a line that provides both gain and offset to the normal signal path may be controlled light source can be used to information. More complex schemes made, including making connections stimulate a self-calibration process. All can be used to adjust for nonlinearities. to simulate zero scale and full scale of these replace mechanical calibration readings for example. Another use procedures in factory settings and of these interruptions would be, for within the equipment itself. The digital example, to cut a signal path gain in approach provides a range of benefits: half and check that the response is better reliability, improved employee indeed exactly half. If not, an offset safety, increased dependability, and error is indicated and can be corrected reduced product liability expense. for. In the latter case, where full system In addition, digitally controlled operation needs to be maintained, calibration can be fully automated, out-of-band or noise level techniques which results in reduced test time and can be used by injecting signals either expense by removing human error. above or below the normal signal frequency range, or signals so small Solid state solutions such as digital that they fall within the noise floor of pots as opposed to mechanical pots the system. With proper design, these are not susceptible to mechanical signals are detectable by a variety of shock and vibration, which can cause methods. These can be used to stimulate loss of calibration settings and, in the the test and calibration protocol while case of mechanical pots, can cause standard signal processing continues. momentary wiper contact bounce The techniques used are limited only which will likely lead to unpredictable by the creativity of the engineers. If a and potentially dangerous behavior. Figure 4. A digital multimeter showing good calibration of the system, during a readjustment, detects zero signal level, but is the gain calibrated? This is difficult to Analog switches have improved to that no further adjustment is possible, discern without a reference standard to read periodically. Or, the point that their on-resistance is then an alarm condition must be set. maybe during power-up it reads a precision internal value while low enough that they can be used in the display is blanked to check for proper gain calibration? The ability to adjust analog outputs high-precision gain setting circuits to using digital technology has greatly provide a range of precision fixed-gain Continuous Monitoring and enhanced the ability to continuously choices. This capability, combined Readjustment monitor and adjust. Digital technology with a digital pot for fine adjustments In some applications, waiting for provides low-cost and nearly error- within a gain range, can provide an periodic calibration at power-up would free communications for remote extremely precise calibration capability.

Calibration and Automated Calibration 137 The first type of reference, a trimmable Implementing Leveraging Precision CRef, enables a small trim range, Electronic Calibration Voltage References for typically 3% to 6%. This is an advantage Digital pots, which can guarantee Digital Calibration for gain trim in industrial imaging 50,000 write cycles, allow periodic systems. For instance, coupling a video Sensor and voltage measurements adjustments to occur repeatedly over DAC with a trimmable CRef allows the with precision ADCs are only as long equipment life spans. Conversely, overall system gain to be fine-tuned good as the voltage reference used the best mechanical pots can support by simply adjusting the CRef voltage. for comparison. Likewise, output only a few thousand adjustments. control signals are only as accurate The second type, an adjustable reference, Location flexibility and size are also as the reference voltage supplied to allows adjustment over a wide range advantages. Digitally adjustable pots the DAC, amplifier, or cable driver. (e.g., 1V to 12V), which is advantageous can be mounted on the circuit board for field devices that have wide-tolerance directly in the signal path, exactly where Common power supplies are not sensors and that must operate on they are needed. In contrast, mechanical adequate to act as precision voltage unstable power. Some examples, such as pots require human access, which can references. They typically are not portable maintenance devices, may need necessitate placing them in nonoptimal designed to meet the accuracy, to operate from batteries, automotive locations that result in long circuit traces temperature coefficients, and noise power, or emergency power generators. or with designers having to resort to specifications needed in a voltage using coaxial cables to make the proper reference. All voltage sources have The third type, called an E2Ref, noise-shielded connections. In sensitive some imperfect specifications for integrates memory, allowing a single- circuits, the capacitance, time delay, or power-supply rejection ratio (PSRR) pin command to copy any voltage interference pickup of these connections and for load regulation, but typically a between 0.3V and (VIN - 0.3V) and, can reduce equipment precision. voltage reference will have very good then, to infinitely hold that level. PSRR specifications. The load range E2Refs benefit test and monitoring Digital pots used in electronic calibration allowed is usually far less than a power instruments that need to establish a schemes can be fundamental in supply’s load range, which reduces its baseline or warning-alert threshold. eliminating these types of problems. output voltage tolerance. No control In addition, calibration DACs (CDACs) system can have infinite gain while Summary and calibration digital pots (CDPots) remaining stable, so there will always Electronic and automated calibration also enable electronic trimming, be some loading effect on the output techniques are becoming mainstream adjustment, and calibration. These voltage of a voltage reference. because they make production more calibration-specific devices often employ efficient and products last longer. New internal nonvolatile memory, which Compact, low-power, low-noise, and products like CDACs and lower cost automatically restores the calibration low-temperature-coefficient voltage precision DACs, digital pots, and CRefs setting during power-up and provides references are affordable and easy to from Maxim provide an economical the ability to customize the calibration use. In addition, some references have way to incorporate calibration circuitry granularity to match the application. internal temperature sensors to aid in directly into end products to minimize the compensation for this environmental For extra safety, one-time programmable downtime, reduce costs, and improve variable. Voltage references with (OTP) CDPots are available. These long-term performance, even under “force” and “sense” pins further improve devices can permanently lock in harsh operating conditions. accuracy by removing the slight voltage the calibration setting, preventing effects of ground currents in the circuit. an operator from making further adjustments. To change the calibration In general, there are three kinds of serial value, the device must be physically calibration voltage references (CRefs), replaced. A special variant of the OTP each of which offers unique advantages CDPot always returns to its stored value for different factory applications. Having upon power-on reset, while allowing a choice of serial voltage references operators to make limited adjustments enables the designer to optimize during operation at their discretion. and calibrate with high accuracy.

138 Control and Automation Solutions Guide Recommended Solutions

Part Description Features Benefits CDPots MAX5481 1024-tap (10-bit) CDPot with SPI or 1.0µA (max) in standby, 400µA Minimal power use for battery- up/down interface (max) during memory write operated portable devices. MAX5477 Dual, 256-step (8-bit) CDPot with EEPROM write protection, single- EEPROM protection retains I2C interface supply operation (2.7V to 5.25V) calibration data for safety. MAX5422 Single, 256-step (8-bit) CDPot with Tiny (3mm x 3mm) TDFN package Saves PCB space for portable SPI interface products. MAX5427 32-step (5-bit), OTP CDPot OTP or OTP plus adjustment Versatile, reduces component count by performing two functions. DS3502 128-step (7-bit) CDPot with I2C High output voltage range (up to Permits direct calibration of high- interface 15.5V) voltage circuits. CDACs MAX5105, MAX5115 Quad, 8-bit CDACs with Rail-to-rail output buffers, choice Selectable voltage range improves independent high and low of I2C or SPI interface granularity and prevents unsafe reference inputs adjustments. MAX5106 Quad, 8-bit CDAC with Allows customization of calibration Saves PCB space for portable independently adjustable voltage granularity, small 5mm x 6mm products. ranges package MAX5214/MAX5216 Ultra-low-power, 1-channel, Quiescent current < 80µA max, SPI High resolution and external 14-/16-bit voltage-output DACs interface reference provides fine granularity and flexibility for automated calibration systems. MAX5715* Quad, 8-/10-/12-bit DACs with 8-/10-/12-bit voltage-output DAC, High integration provides multiple internal reference three-voltage-selectable internal calibration points in a small space. reference, SPI interface MAX5725* Octal, 12-bit DAC with watchdog 8-/10-/12-bit resolution, selectable Watchdog timer allows resets to timer and internal reference internal reference, watchdog timer, defined calibration levels in event SPI interface of communication failure. CRefs and E2Refs MAX6160 Adjustable CRef (1.23V to 12.4V) Low 200mV dropout, 75µA supply Longer battery life in portable current is virtually independent of equipment. input-voltage variations MAX6037 Adjustable CRef (1.184V to 5V) Shutdown mode (500nA, max), low Battery friendly and small size for 100mV (max) dropout at 1mA load, portable applications. 5-pin SOT23 (9mm2) MAX6173 Precise voltage reference with ±0.05% (max) initial accuracy, Allows analog system gain trim temperature sensor ±3ppm/°C (max) temperature while maintaining the digital stability accuracy of ADCs and DACs. MAX6220 Low-noise, precision voltage 8V to 40V input-voltage range, Dependable operation from reference ultra-low 1.5µVP-P noise (0.1Hz to unstable power (batteries, 10Hz) automotive power, or emergency power generators). DS4303 Electronically programmable Wide, adjustable output voltage A calibration voltage is memorized voltage reference range can be set within 300mV forever using one simple GPIO pin. of the supply rails with ±1mV accuracy

*Future product—contact the factory for availability.

Calibration and Automated Calibration: Recommended Solutions 139 140 Control and Automation Solutions Guide Legal Notices

141 142 Control and Automation Solutions Guide Trademark Information

iButton is a registered trademark of Maxim Integrated Products, Inc. µMAX is a registered trademark of Maxim Integrated Products, Inc. 1-Wire is a registered trademark of Maxim Integrated Products, Inc. CompoNet is a trademark of OMRON Corporation. HART is a registered trademark of the HART Communication Foundation. HomePlug is a registered service mark of HomePlug Powerline Alliance, Inc. Hygrochron is a trademark of Maxim Integrated Products, Inc. IEEE is a registered service mark of the Institute of Electrical and Electronics Engineers, Inc. IO-Link is a registered trademark of PROFIBUS User Organization (PNO) . Linux is a registered trademark of Linus Torvalds. LonTalk is a registered trademark of Echelon Corp. LonWorks is a registered trademark of Echelon Corp. MAXQ is a registered trademark of Maxim Integrated Products, Inc. MICROWIRE is a registered trademark of National Semiconductor Corporation. Modbus is a registered trademark of Schneider Automation, Inc. NovaSensor is a registered trademark GE Infrastructure Sensing, Inc. The PROFIBUS PROCESS FIELDBUS logo is a registered trademark of PROFIBUS and PROFINET INTERNATIONAL (PI). THINERGY is a registered trademark of Infinite Power Solutions, Inc. QSPI is a trademark of Motorola, Inc. Wi-Fi is a registered certification mark of Wi-Fi Alliance Corporation.

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