Voltage regulator

wangtao Simcom Hardware Dept.2 Agenda

Voltage regulator presentation:

• AC-AC

• DC-AC

• DC-DC Agenda

DC-DC Voltage regulator presentation:

• LDO

• ( less DC-DC)

• DC-DC (inductor) LDO

• LDO ( Low Dropout) LDO is a

• Dropout voltage output voltage within 100mV, (Vin – Vout) min LDO LDO

Working principle: The voltage divided by R1 & R2 is compared with the internal reference voltage by the error The MOSFET, which is connected to the Vout pin, is then driven by the subsequent output signal. The output voltage at the Vout pin is controlled & stabilized by a system of negative feedback. LDO parameters • Input Voltage The minimum Vin must be larger than Vout + VDO, independent from the minimum value given in the selection table.

• Efficiency By neglecting the quiescent current (Iq) of the LDO, efficiency can be calculated as Vout/Vin. LDO parameters

• Power Dissipation PD = (Vin – Vout) x Iout; PD is limited by package. Compare with step down buck DC-DC, for higher power dissipation or requirements for higher efficiency, recommend buck.

• Requirements The output capacitor and especially Equivalent Series Resistance (ESR) are critical for stability.

• Noise and PSRR Select an LDO with high rejection ratio (PSRR) for noise immunity from the input supply and low output noise. Some LDO have a bypass (BP) pin for adding capacitance to lower the output noise. LDO parameters

Ceramic Capacitor Equivalent Circuit • Equivalent Series Resistance (ESR) is a critical factor in circuit performance • Capacitor Impedance is a function of: – Cap Value, ESR and Frequency LDO parameters Things to know about Ceramic Caps: ESR is a function of: •Physical size • Larger case size caps have lower ESR •Material Type X7R – Best (lowest ESR) X5R – Good Y5V – Low cost (highest ESR) Capacitance vs. Frequency: •Capacitance value becomes smaller as frequency increases (impedance drops) •Again material type has an effect LDO parameters

X7R Material MLCC Y5V Material MLCC •Lower ESR •Higher ESR •Lower impedance •Higher impedance •Better Capacitance vs. Frequency •Poor Capacitance vs. Frequency •Good Temp. Tolerance (+/- 10%) •Poor Temp. Tolerance (+20/- 80%) Regulator Overview

LDO selection:

• LOW noise, HIGH PSR

• No enough PCB area (inductor less)

• Low voltage drop

• Low cost Charge Pump Types of Charge Pump Devices: Types of Charge pump devices are available in different topologies:

Voltage Doubling (2X) Charge Pumps • Vout = 2 x Vin

Fractional Charge Pumps • Vout = N x Vin, where N = device multiplication – Example: Vout = 1.5 x Vin

Regulated Output Charge Pumps • Can be 2x, 3x, Fractional, etc. Voltage Double Charge Pump

Working principle:

VIN

Cin S1 S3 C+ CONTROL Cfly SHDN / CLOCK

S2 S4 C-

VOUT

Cout GND

Voltage double charge pump block diagram (Vout = 2 x Vin) Voltage Double Charge Pump

Charge Pump Phase Cycle 1: Charge Pump Phase Cycle 2: Charge CFLY Bootstrap CFLY to the Output

I VIN I + VIN CIN - S2 S1 CIN + S2 S1 CFLY + - CFLY S4 S3 - S4 S3

VOUT VOUT COUT + COUT -

Equivalent Circuit for Equivalent Circuit for Phase Cycle 1: Phase Cycle 2: VOUT + VIN CFLY + + - + CIN CFLY VIN COUT + - CIN - Fractional Charge Pump

Working principle: Fractional Charge Pumps: • Fractional charge pumps offer a technique to CONTROL / ENABLE multiply an input voltage OSCILLATOR by a non-integer multiplication factor • Fractional charge pumps can have efficiency VIN S1 advantages in low output CFLY1 CIN voltage applications S2 VOUT

S3 COUT CFLY2

S4 Fractional Charge Pump

Fraction Charge Pump Works: •Operates with 2 switching cycle phases (same as a voltage doubling charge pump) •Two “Flying” are used: •In the first switching cycle CFLY1 and CFLY2 are connected in series and placed across Vin, which effects a at Vc = Vin/2 for each “Fly” capacitor. •In the second switching cycle CFLY1 and CFLY2 are connected in parallel, then switched to be in series between Vin and Vout. •Vout = Vin + Vin/2 = 1.5 x Vin

Equivalent Circuit for Equivalent Circuit for Phase Cycle 1: Phase Cycle 2:

VIN VOUT VOUT + + + VIN CFLY2 VIN 2 CFLY1 CFLY2 + - + 2 - - + COUT VIN CIN - VIN COUT - + VIN + - CFLY1 2 CIN - VIN - Regulated Charge Pump

Working principle: Regulated Charge Pumps: • Regulated charge pumps are voltage doubling, VIN tripling or fractional Cin S1 S3 C+ charge pumps with an SHDN CONTROL Cfly output system and feedback C- S2 S4 control. VOUT VREF • Regulated charge pumps Cout can provide a stable + output voltage from a

- varied input supply, which is ideal for battery operated devices. GND Charge Pump Efficiency

Primary items which effect efficiency:

•RDS(ON) of the MOSFET switching devices -I2R Loss – Lower RDS specs are better

•Operating quiescent current

•Vin versus Vout for a given charge pump topology

-This applies to regulated charge pumps •Types of external capacitors used -Cin, Cout and Cfly Charge Pump Efficiency

Efficiency of Regulated Charge Pumps:

• Regulated Voltage Doubling Charge Pumps

Fixed output voltage level Input voltage may vary with in the device operating range The input voltage is doubled, then regulated down to the desired output voltage.

• Theoretical Efficiency =  = VOUT / 2VIN

Example: VIN = 2.8V, VOUT = 3.3V,  = 58.9% Example: VIN = 3V, VOUT = 4.5V,  = 75% Charge Pump Efficiency

Efficiency of Fractional Charge Pumps:

• Regulated Fractional Charge Pumps

Fixed output voltage level Input voltage may vary with in the device operating range Fractional charge pumps have an advantage in low voltage applications since the Input to Output difference voltage to be regulated is small.

• Theoretical Efficiency =  = VOUT / 1.5VIN

Example: VIN = 2.8V, VOUT = 3.3V,  = 78.6% Example: VIN = 3V, VOUT = 4.5V,  100% External component selection

External Component Selection: • Charge pump devices typically require 3 to 4 external capacitors depending upon circuit topology.

• The CIN/COUT to CFLY ratio can range from 1:1 to 10:1 • Capacitor value and properties are critical to good charge pump performance Important Capacitor Characteristics: • Capacitor value • Dielectric material type • Physical size • Capacitor equivalent series resistance (ESR) External component selection

Capacitor selection: • Ceramic Capacitors are typically the best choice – Ceramic capacitors are non-polarized and have low ESR characteristics, typically <100m • Ceramic Capacitor ESR: • Capacitor ESR has a dramatic effect on output • ESR can vary depending capacitor type, value and case size. • X7R Dielectric is the best (higher cost) • X5R Dielectric is good • Y5V Dielectric is poor (lower cost) • Tantalum and Aluminum Electrolytic Capacitors – These types of capacitors may be used with charge pumps for Cin and Cout at the expense of performance • Both have high ESR characteristics • Output ripple and efficiency will be compromised

• CFLY must be a non-polarized capacitor (bi-directional current flow) Charge pump – output ripple

Output Ripple Characteristics: Output ripple is significantly effected by the external capacitor value. The following plots are examples measured with an AAT3111 showing how capacitor value can effect output ripple.

AAT3111: VIN = 3.0V, VOUT = 5.0V, ILOAD = 50mA

0805 Size, X7R Ceramic 0805 Size, X7R Ceramic 0805 Size, X7R Ceramic CIN = COUT = 2.2uF CIN = COUT = 4.7uF CIN = COUT = 10uF CFLY = 0.22uF CFLY = 0.47uF CFLY = 1uF Vripple = 60mVp-p Vripple = 45mVp-p Vripple = 30mVp-p Charge pump – output ripple

Output Ripple Characteristics: Output ripple is significantly effected by the external capacitor material type. The following examples were measured with an AAT3110 showing how equal value and size capacitors of different material types can effect output ripple.

AAT3110: VIN = 3.0V, VOUT = 5.0V, ILOAD = 50mA

0805 Size, Y5V Ceramic 0805 Size, X7R Ceramic CIN = COUT = 10uF CIN = COUT = 10uF CFLY = 1uF CFLY = 1uF Vripple = 90mVp-p !!! Vripple = 35mVp-p DC-DC three basic switching topologies in common Types of DC-DC devices are available in three topologies: BUCK Step-down power stage. Power supply designers choose the buck power stage. the required output voltage is always lower than the input voltage

BOOST step-up power stage. Power supply designers choose the boost power stage. the required output voltage is always higher than the input voltage

BUCK/BOOST step-up/down power stage. Power supply designers choose the buck-boost power stage. the output voltage is inverted from the input voltage, and the output voltage can be either higher or lower than the input voltage. DC-DC

Q1 L1 Step Down “Buck” Converter Vin+ Vout+  Vout1 VD in D Cin D1 Cout V V out in Vin- Vout-

L1 D1 Step UP “Boost” Converter Vin+ Vout+ V V  in Q1 out 1 D Cin Cout

Vout V in Vin- Vout-

D1 Step Up / Step Down Q1 L1 Vin+ Vout+

“Buck - Boost” Converter D1  Cin Q2 Cout 1Vin D D V  Vin- Vout- out 1 D

Vin V out  V in DC-DC PWM Control Signal Details

• DC steady state assumes VOUT and VIN are constant • Steady state dictates that the average inductor voltage must be zero (volt-sec balance) • The inductor DC current is equal to the load current…no DC current into the output cap …constant output voltage

Vin=3.75V Vin=5.0V D=ton/Ts Vin V out  DV out  (1D)- V V  D Voltage o in 0 ton Vo 2.5V D1   0.67 -Vout Vin 3.75V Ts

Vo 2.5V Io Ipp D2   0.5 Current Vin 5.0V 0 Inductor Waveforms DC-DC

Basic Step-Down “Buck” DC/DC Converter • Simple Control • 80-90 % efficiency at full load • Switching frequency 30kHz -4 MHz • Light load efficiency improvement with burst mode, frequency shift or pulse skipping

Q1 L1 Vin+ Vout+

Cin D1 Cout

Vin- Vout- DC-DC PWM Switching Control: • Output Voltage is the average of the voltage applied to the output LC filter

Vout+ Vin L1 gnd ton Cout Ts D=ton/Ts Vout- Vout=D*Vin DC-DC

Synchronous Step-Down DC/DC Conversion – More efficient than a conventional – Eliminates the external Schotky – Required “dead-time” break before make switching to limit shoot-thru current and improve efficiency • Made possible by use of CMOS process technology – Light Load Efficiency Improvements • Pulse skipping or Burst Mode at light load to reduce switching losses

L1 Control Mosfet M1 Vin+ Vout+ Synchronous Cin Mosfet Cout M2

Vin- Vout- DC-DC Synchronous Switching “Dead-Time” • What is it? – Time when both control and synchronous are off • Advantage – Eliminates Mosfet shoot-thru current and associated losses – Reduces switching losses associated with the turn on of the synchronous (VDS is zero when VGS is applied) • Disadvantage

– Diode body losses are greater than Mosfet RDS(ON) losses for the same current during the dead time. • Solution – Design synchronous converters with good break-before-switching – Use a very high switching frequency – Sub-micron CMOS and BCD process allow the solution to be possible DC-DC

Synchronous Switching States M1 Vin+ Vout+ L1 M1 L1 Vin+ Vout+ Cin Cout

Cin Cout M2 Vin- rtn

Vin- Vout- L1 Vo+

D=ton/Ts Ts M2 Cout

Voltage ton rtn L1 Control FET 0 Vout+ Sync FET 0 Body Cout Body Diode 0 rtn DC-DC Soft-Start is Very Important Switchers • Reduces In-rush currents during start-up • Limits supply rail voltage sag at start-up

Soft-Start switcher turn-on Switcher turn-on response response without soft-start DC-DC

Typical IOUT Current Limit Response

ILIMIT at 1.2A for VOUT = 3.3V

ILIMIT at 1.3A for VOUT = 1.5V DC-DC

High vs Low Switching Frequency • High switching frequencies: – Typical switching frequencies above 800kHz – Allow for the use of small external components • Output and capacitors – Permit the use of switching converters in RF applications • High switching frequencies are less likely to interfere with baseband systems – Good Transient response – Lower switching ripple • Low switching frequencies: – Typical switching frequencies from 20kHz to 800kHz – Poor transient response – Large external components – High switching ripple and noise – Low cost / performance switching converts External component selection External Component Selection:

Good performance is dependant upon the right external component selection – Output Capacitors – Ceramic Capacitors – Applies to both Switching and Linear (LDO) Regulators – Output Inductor – Inductors – Wound – Multilayer Chip – Diode External component selection

Capacitor selection:

• The Capacitor should be low ESR – Minimized switching noise and ripple – For best transient response • Different Material Types – Effect performance – X7R, X5R and Y5V are most common • One must balance circuit performance vs. size and cost limitations External component selection Inductor selection:

• The inductor should be low ESR – For best power conversion efficiency – Minimized switching noise and ripple • Low Height profile – If used in portable products • Magnetic shielded – If used in wireless / RF applications • One must balance circuit performance vs. size and cost limitations Wire Wound Ferrite inductor

Wire Wound Ferrite inductors are superior for switcher applications Strengths: •Large inductance value range •High output current capabilities •Lowest ESR inductor •Maximized power conversion efficiency •Minimized switching noise and ripple Weaknesses: •Larger physical size, pcb footprint and height •Magnetic shielding is not available for all package types or sizes •Higher cost Multilayer Ferrite inductor

Multilayer Ferrite inductors are ok for switcher applications Strengths: •Low inductance values ok for high switching frequencies •Small physical size, reduced pcb footprint and low height profile •Magnetic shielded •Lowest cost Weaknesses: •Limited output current capabilities •Higher ESR inductor •Reduced power conversion efficiency •Higher switching noise and ripple Regulator Overview

DC-DC Selection Basic:

• Provide good power conversion efficiency over a wide range of input and output

• Provide high output current Regulator Overview

Typical DC/DC Switcher Application Typical LDO Application

Switch-Mode Regulators Linear Regulators

High Efficiency, up to 95% Poor Efficiency, when VIN >>VOUT High Noise and Ripple Low Noise and Ripple Higher Power Density Simple

Higher Current Capability IOUT Thermally Limited Highly design dependant Fast Transient Response

Step Up or Sep-Down → Vin ≤ Vout ≤ Vin Step Down Only → Vout ≤ Vin