Perfect L.L.C. 1 of 12 AS0705-R1

POWER-GATE (Generation 4.0) Application Sheet

CONDUCTOR SIZING IMPORTANCE assuming the device is operating within its current limitations outlined in the The MOSFET array used in the generation specification sheet, either the external 4.0 POWER-GATE relays has been conductors are undersized for the current designed to provide industry-leading, ultra- flowing through the device, the ambient low on-state resistance. This results in temperature surrounding the device is in extremely low voltage drops at continuous excess of the maximum rating, or a currents up to 600 A and surge currents up combination of both. The system should to 3000 A, even at an ambient temperature then be shut down and the thermal of over 100 °C (212 °F). In order to conditions reevaluated so as to ensure the maintain a low-voltage drop (and, device’s continued reliability. consequently, low internal power dissipation), it is essential that the cables or HIGH CURRENT TURN-OFF AND bus bars connected to the device are SYSTEM LOOP properly sized for the currents expected in the application. Undersized conductors can Device reliability is also greatly affected by cause heat to be transferred into the relay, the system loop inductances during turn-off which will cause the MOSFET array conditions. When operating at the high resistance to increase, negating the low currents the MOSFET array was designed resistance the relay was designed to provide. for, the total of the external Additionally, when operating at high world it is connected to must be carefully continuous currents and ambient evaluated to ensure that under worst-case temperatures, the extra heat from the conditions, the device will be able to safely undersized conductors can raise the internal dissipate the large amount of energy stored junction temperatures of the MOSFETs in the inductance’s magnetic field. beyond their safe operating area, generating the potential for failure. Figures 1 and 2 show a common use of the relay, which is to connect/disconnect a DC Typical applications use cable gauges source to/from any number of arbitrary loads anywhere from 4 to 4/0 AWG (with (including ones with high inductance, such insulation ratings of at least +105 °C) as a winch motor, for example), essentially depending on the continuous current rating, as a replacement for a traditional solenoid. but other system parameters such as Figures 1a and 2a depict the current flow (as increased cable thermal resistance due to indicated by the dotted line) originating bundling and very high duty cycles at high from the source, passing through the currents may dictate the use of paralleled MOSFET array (represented as a simple cables or large bus bars coupled with forced switch in parallel with a body ) to the airflow. Ultimately, it is up to the user to loads (which are assumed to have significant determine the appropriate external conductor inductance), and finally returning to the to be used in any particular application. source. The inductance of the interconnecting cables is shown, but that of If the device flashes an over-temperature the common ground node has been omitted warning (which occurs when the internal for simplicity (although they must be device temperature exceeds +135 °C), then, considered as well when calculating the

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(a)

(b)

Figure 1: High current turn-off transient behavior with system loop inductances (uni-directional relay). (a) Relay shown in closed state (MOSFET array represented by simple switch in parallel with body diode) powering a highly inductive load. (b) Current paths during magnetic field decay, after MOSFET array has completely opened.

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(a)

(b)

Figure 2: High current turn-off transient behavior with system loop inductances (bi-directional relay). (a) Relay shown in closed state (MOSFET array represented by two simple in series, with each switch having a parallel body diode) powering a highly inductive load. (b) Current paths during magnetic field decay, after MOSFET array has completely opened.

February 20, 2018 Created by: Peter Srsic Perfect Switch L.L.C. 4 of 12 AS0705-R1 system loop inductance). it to the settings loaded in the device firmware. The lowest level has a typical In Figures 1b and 2b, the MOSFET array threshold of 2 times the maximum rated has completely turned off in response to continuous current (I L,CONT(MAX) ) and a delay either a user request from one of the time of one minute (see specification sheet triggers, or from an internal detection of a for threshold and delay tolerances); i.e. if the current, voltage, or temperature-related current flowing through the MOSFET array fault. In many cases, the magnetic field exceeds and stays above the threshold for energy in the system inductance (usually one minute (while simultaneously not dominated by the load, but also including exceeding any of the other over-current or interconnect contributions), will not be able short-circuit thresholds for their respective to decay within the MOSFET array’s short delay periods), the microcontroller will turn-off time. Consequently, current is determine that a level one over-current event forced through the MOSFET protection has occurred and will command the circuitry, flyback diode, or both, until the MOSFET array to turn off to protect from field energy has completely dissipated. The over-heating. It will also flash the red fault length of time this process takes is LED with the blink pattern assigned to the dependent upon the magnitude of the current level (see section “FAULT LED when the MOSFET array completes turn- DIAGNOSTICS”). Table 1 summarizes all off, and the total inductance through which the over-current and short circuit thresholds it is flowing. and delay times; it is important to note that these settings are specifically designed to The specification sheet details the maximum protect the MOSFET array under worst-case allowable current upon turn-off (i.e. conditions, while also allowing the passage interrupting current) at various system loop of large surge currents, and, therefore, inductances and temperatures, conditions cannot be modified by end-user request. which should always be adhered to in order to ensure maximum device reliability. If an If at any time the relay opens due to either application has system loop inductances that an over-current or short-circuit condition, it exceed those detailed in the specification can be reset by a toggle of the main trigger sheet, additional external protection may be (be it remote or on-board) after a 10 second required. lockout period. It is up to the user to determine if the cause of the shutdown is OVER-CURRENT AND SHORT- simply due to a request by the loads for too CIRCUIT PROTECTION much current, or if there exists a true fault (e.g. a short-circuit) in the system. The POWER-GATE generation 4.0 relays are equipped with five levels of over-current OVER-TEMPERATURE PROTECTION protection, and a single short-circuit level. In a uni-directional relay, these features The POWER-GATE generation 4.0 relays operate on current flowing from source-to- come equipped with over-temperature load only, while in a bi-directional relay the shutdown to protect both the MOSFET array features operate on currents flowing in either and circuitry from overheating. Should the direction. It achieves this functionality by internal temperature ever reach ~ +135 °C, constantly monitoring the current flowing the MOSFET array will be opened and the through the MOSFET array and comparing red fault LED will flash the blink pattern

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Fault Mode Threshold Delay CIRCUIT BREAK FEATURE Over- 2 x Current 60 s As stated earlier, the over-current and short- I Level 1 L,CONT(MAX) circuit features are used to protect the Over- MOSFET array from damage and cannot be 3 x Current 1 s changed or disabled. However, applications I Level 2 L,CONT(MAX) exist where a circuit-break is required for Over- load protection, but the standard over- 3.25 x Current 500 ms current and short-circuit settings are I Level 3 L,CONT(MAX) insufficient (e.g. open the relay when the Over- load current exceeds 1.5 x I L,CONT(MAX) for 3.5 x Current 200 ms one second). For cases such as this, the I Level 4 L,CONT(MAX) POWER-GATE generation 4.0 relays are Over- available with two circuit-break levels; in a 3.75 x Current 20 ms uni-directional relay, these features operate I Level 5 L,CONT(MAX) on current flowing from source-to-load only, Short- 4 x while in a bi-directional relay the features 4 ms max can be programmed to operate on currents Circuit IL,CONT(MAX) flowing in either direction (e.g. one circuit- Table 1: Summary of over-current and short- break level can be used to open the path circuit thresholds and delays (over-current levels between a source and a load during have a maximum detection time of 15 ms that discharge, while the second level can be should be added to delay time for overall response; short-circuit delay time noted includes used to open the relay at a different value detection time) during charging of the source from a charger attached to the load side). Should the associated with that feature (see section MOSFET array open due to a circuit-break “FAULT LED DIAGNOSTICS”). When condition, the red fault LED will flash the the internal temperature falls below ~ +130 blink pattern associated with that feature °C, the relay will resume normal operation. (see section “FAULT LED [NOTE: While the relay is in its over- DIAGNOSTICS”). temperature mode, it will continue to monitor the source voltage, along with the The relay can be programmed with one of main and override trigger states. For three available reset options: 1) Main example, if the main trigger state changes trigger toggle (exactly the same method used while an over-temperature condition is to reset the relay after an over-current or present, then upon disappearance of that short-circuit shutdown), 2) limited auto-retry condition, the MOSFET array will revert to where the relay will reset a user-defined the position commanded by the current state number of times before reverting to main of the trigger, as opposed to the one that was trigger toggle mode, and 3) unlimited auto- present when the condition first appeared. retry where the relay will continuously Similarly, if an enabled under-voltage attempt to reset itself indefinitely. All three condition appears while in over-temperature of these reset methods require a minimum mode, then upon exiting that mode, the reset delay of 10 seconds (i.e. the lockout MOSFET array will remain open even if the period, same as that for an over-current or main trigger is commanding it closed (unless short-circuit shutdown). the override trigger is active).]

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UNDER- AND OVER-VOLTAGE type switch is used to activate the override trigger. This ensures that the MOSFET An additional feature of the POWER-GATE array will default to the open position when generation 4.0 relays is the ability to open the relay detects an under- or over-voltage the MOSFET array should the source condition, unless the user purposefully voltage fall and stay below a user-defined actives the override trigger; use of a non- threshold for a user-defined period of time momentary switch creates the possibility (often used to protect a battery from deep that the user can accidentally leave the relay discharge or loads from an over-voltage in the override state, which can drain the condition). The voltage threshold can be set source even though the user is expecting the in 0.1 V increments over the entire operating protection to be active. voltage range (see specification sheet); the delay time can be set in 20 ms increments SLEEP MODE (see specification sheet for the minimum available response time) up to any practical The POWER-GATE generation 4.0 relays maximum length of time. were designed to draw very little operating current (< 20 mA open, < 23 mA closed), Up to four under-voltage and four over- especially with respect to the large amounts voltage threshold/delay combinations are of current the MOSFET array can pass. available to provide the user with maximum However, in some applications even this source voltage monitoring flexibility. For small amount of current can be problematic example, in a 12 V automotive application (e.g. the case where a vehicle is stored the user may set two under-voltage levels, unused for days or weeks). To one for relay opening when the battery drops accommodate applications where minimal and stays below 12.0 V after 1 hour operating current is a priority, the relays can [allowing for a period of time that it can be programmed with a low-power “sleep” power loads when the vehicle’s charging mode. system is not operating (e.g. the engine is not running) before being disconnected], and Whenever the relay enters an idle state [i.e. the other for immediate relay opening when 1) no timers for voltage- or current-related the battery drops below 11.0 V (to protect features, or trigger delays, are running, 2) the battery from yielding a vehicle no-start the relay is not in an over-temperature, over- condition). current, short-circuit, circuit-break, or blown-fuse fault mode, and 3) if the Once an under- or over-voltage condition is MOSFET array is closed, the current passed detected, the MOSFET array will open (if it is less than the sleep threshold (see is closed) and the red fault LED will turn specification sheet)] the MCU will begin a steady on (if a circuit-break, over-current, timer, set at a value specified by the short-circuit, or over-temperature condition customer (e.g. 24 hours). If at any time one is not already present; see section ” FAULT or more of the conditions specified in the LED DIAGNOSTICS” for more preceding parenthesis change (the “idle information). While in the under- or over- conditions”), the timer will be reset, and will voltage mode, the override trigger can be not restart until the relay once again enters used to force the relay closed, assuming the an idle state. main trigger is also active. Word of caution: It is highly recommended that a momentary-

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Should the relay remain in an idle state the cleared, the fault LED will begin to flash the entire duration of the sleep timer, the over-temperature pattern). MOSFET array will be opened (if it is not already) all LEDs will be turned off, and the EXTERNAL LEDS relay will go into its low-power mode where the operating current falls to < 2.5 mA under The POWER-GATE generation 4.0 relays worst-case conditions. Every ~33 seconds also come equipped with a harness used to (the watchdog period as defined in the connect external LEDs for device status and specification sheet) the relay will be restored fault monitoring. Every on-board LED is to the state it was in just prior to entering the duplicated on the harness so that all sleep mode and will begin monitoring all functionality, operating states, and fault voltages and the MOSFET array current. conditions can be monitored from a remote Should any of the idle conditions change (or, location, such as a vehicle’s cabin. While if the under-voltage feature is enabled, the not required for operation, the external source voltage is measured to be above the LEDs are highly recommended so that fault under-voltage reset value), the relay will conditions such as over-current, over- permanently exit the sleep mode and normal temperature, or a blown fuse can be operation will commence; if none change immediately detected and resolved before within approximately 66 ms, the relay will device health is put at risk. go back into its low-power mode for another 33 second window. The relay can also be The outputs are of the open-drain type, with woken from its sleep mode by a change-of- an in-line incorporated to state of either the main or override trigger. protect the MOSFETs from an accidental reverse voltage condition (see functional All three of the wake-up methods (timer, block diagram on the specification sheet). main trigger state-change, override trigger Consequently, they can be used not only state-change) can be enabled/disabled with external LEDs, but with any other independently, providing maximum sleep monitoring system that has its own pull-up mode management flexibility. scheme (e.g. an external computer), as long as the maximum current and voltage as FAULT LED DIAGNOSTICS detailed in the specification sheet are adhered to. As the reader will have gathered by this point, the red LED is used to indicate that FUSE the MOSFET array has opened due to a fault and has various illumination patterns to Like all POWER-GATE devices, the identify the particular fault mode that is generation 4.0 relays uses a fuse in order to active. Table 2 summarizes the illumination protect the flyback diode from a reverse patterns for each possible fault mode, along battery condition. If this fuse should blow, with their priority (higher number = higher the “FUSE OPEN” LED will illuminate. Do priority; e.g. if both the over-current and the not replace the fuse with any other than that over-temperature fault modes are present, specified by the manufacturer. the fault LED will flash the over-current pattern; if the over-temperature fault is still present when the over-current fault is

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FAULT LED DIAGNOSTIC TABLE Dark Illumination Number Blink Blink Time Priority Fault Mode Pattern of On- Off- Between

Type Blinks Time Time Blink Sets Short- ¼ ¼ 2 Blinking 6 3 Circuit second second seconds Over- ¼ ¼ 2 Current Blinking 5 3 second second seconds Level 5 Over- ¼ ¼ 2 Current Blinking 4 3 second second seconds Level 4 Over- ¼ ¼ 2 Current Blinking 3 3 second second seconds Level 3 Over- ¼ ¼ 2 Current Blinking 2 3 second second seconds Level 2 Over- ¼ ¼ 2 Current Blinking 1 3 second second seconds Level 1 Circuit- ½ ½ Break Level Blinking 1 - 3 second second 2 Circuit- 1 1 Break Level Blinking 1 - 3 second second 1 1 1 Over- 8 8 Blinking 1 - 2 Temperature second second Under- /Over- Steady - - - - 1 Voltage

Table 2: Summary of red fault LED illumination patterns (1 is lowest priority, 3 is highest priority )

LOSS OF GROUND loss of ground will also cause all LEDs to go dark, immediately indicating to the user that In order to operate properly, the relay the POWER-GATE requires attention. requires a good ground connection. If ground is lost, the internal circuit board will NOTE: If any of the on-board LEDs are not receive power, and thus, will not be able disabled, the corresponding external to properly operate the MOSFET array. connections will be as well. It is possible to This is another reason why use of the enable only the external LEDs, but this external LEDs is highly recommended, as

February 20, 2018 Created by: Peter Srsic Perfect Switch L.L.C. 9 of 12 AS0705-R1 requires the on-board LEDs to be physically the relay to be forced into the open state for removed and is not recommended. safe installation/removal purposes. A remote override trigger can still be with an TRIGGERS autonomous master trigger to force the relay closed when required. MAIN TRIGGER: The MOSFET array is controlled through the main trigger line, On-board AND Non-isolated, Remote which can be configured in five different Types: Some applications require relay ways: 1) Active-high, non-isolated, remote triggering through automated means, such as only, 2) active-low, non-isolated, remote battery management systems (BMS) only, 3) on-board only, 4) on-board AND commonly used with lithium-ion batteries. active-high, non-isolated, remote, and 5) on- While this is a perfectly acceptable board AND active-low, non-isolated, triggering source, using it as the lone remote. method of turning on and off the relay leaves open the possibility of a latch-up Active-high and Active-low Non-isolated condition should that source fail. For Remote Only Types: The most common example, imagine that the relay is connected main trigger option used is the active-high, between a lithium-ion battery and various non-isolated, remote type as it requires only loads, while its trigger line is connected to one wire for control, interfaces with a wide the under-voltage warning output of a BMS; variety of control signals, and has low the intention being that this will trigger the current draw (< 0.8 mA). The active-low, relay open (disconnecting the loads from the non-isolated, remote option may not be as battery) when the BMS detects the batteries easily integrated into a system that generally have been discharged too much and need to uses high-side switched signals (e.g. a 12 V be charged. Should the relay automatically automotive application), but has the lowest open due to an over-current or short-circuit available trigger current draw (< 40 μA) event, while the battery is fully charged (and and, thus, may be preferable in some thus the main trigger line tied to the under- applications. voltage remains in its “ok” state), the on- board switch is required in order to reset the On-board Only Types: Some applications relay, since a master trigger toggle is the only require that the relay respond to voltage method in which this is accomplished. conditions, as opposed to state changes on NOTE: You could also reset the relay by the main trigger; in those cases, the main unplugging and then plugging in the control trigger can be configured in the on-board harness, although this is not generally only type by moving the remote main trigger recommended as it yields undue harness to an on-board switch, simplifying the strain and fatigue. wiring of the POWER-GATE into the larger system. Although the user will rarely Isolated Type: An isolated type of main interact with the relay through the on-board trigger is currently in the design phase and main trigger, it is required for two reasons: will be released shortly as an accessory. It 1) To allow for device reset after the will be useful when the relay and trigger MOSFET array has opened due to a circuit- source have different ground references (e.g. break (if enabled), over-current, or short- relay on a vehicle, trigger originating from a circuit condition (all requiring a toggle of mobile device such as a laptop) or when the the switch to achieve reset), and 2) to allow trigger wire is routed through a high noise

February 20, 2018 Created by: Peter Srsic Perfect Switch L.L.C. 10 of 12 AS0705-R1 environment (i.e. the isolated trigger can be is not accidentally left in the closed state due used to ignore common-mode noise between to an override switch being unintentionally the positive and negative trigger wires). The left in the active position. trade-off for choosing to use the isolated over the non-isolated trigger, however, is the TRIGGER DEBOUNCE AND DELAYS: need for two, instead of only one, control Both the main and override triggers have a wires, and a higher current draw (anywhere minimum hold time on the order of 40 ms, from 2 to 5 mA, depending on the voltage which is used both for mechanical switch difference between the trigger wires). debouncing and noise filtering. Should additional delays be required between a Whenever the main trigger is active the trigger state change and relay response, the MOSFET array will be closed as long as POWER-GATE can be programmed with there is not a circuit-break, under-voltage, or trigger delays in 20 ms increments to any over-voltage condition (if any of those practical value. features are enabled), or an over-current, short-circuit, or over-temperature fault. Trigger debouncing delays can be removed Should a current-related fault cause the for customers that require faster relay MOSFET array to open, the main trigger can response, but a request for such must first be reset the relay through a simple toggle (refer analyzed by Perfect Switch engineering for to specification sheet for minimum trigger approval. hold time to ensure proper reset). LOAD-DUMP TOLERANCE OVERRIDE TRIGGER: If a voltage-related fault is the cause of the MOSFET array The POWER-GATE generation 4.0 relays opening, the override trigger can be used to have been designed to withstand a load force the relay closed (assuming the main dump pulse rated up to the ISO7637- trigger is active), which may be required, for 2:2004[1] pulse 5 specification, as long as example, when powering a load becomes that pulse is externally clamped to a more important than preserving battery life. maximum of 60 V for both the 12 and 24 V Just like the main trigger, the override versions. This feature allows the relay to trigger can be configured as active-high or survive a variety of extreme voltage spikes active-low in the non-isolated remote form, that occur when a load drawing large both with identical electrical specifications amounts of current is suddenly (and, usually, as those of the main trigger (isolated unintentionally) disconnected. override trigger will be added to the same future accessory for the isolated main trigger REVERSE POLARITY PROTECTION type). The standard configuration is the active-low type, which allows the Many applications (in particular, those in the connection of a small switch between the automotive industry) are subject to possible override trigger wires (OVERRIDETRIG+ reverse polarity source conditions; e.g. a and OVERRIDETRIG-) that can be routed replacement battery being installed to a vehicle cabin, for example. NOTE: It backwards. While the on-board fuse will is recommended that a momentary switch likely blow to protect the flyback diode (see type be used for override functionality. This section “FUSE”), no further damage to the ensures that if the relay has detected an relay will occur as long as the reverse under-voltage condition, the MOSFET array voltage conditions stated in the specification

February 20, 2018 Created by: Peter Srsic Perfect Switch L.L.C. 11 of 12 AS0705-R1 sheets are adhered to. In general, a uni- indefinitely at source voltages as low as 4.8 directional relay will only be used between V, and can remain closed during voltage one source and one or more loads, so as long dips to 3 V for up to 7 ms. as the loads are protected against reverse polarity (the load(s) will actually see the UNI-DIRECTIONAL VS. BI- negative source voltage minus the body DIRECTIONAL diode forward voltage drop), then there will be no reverse current flow through body As has been pointed out many times, the and the relay will survive an POWER-GATE generation 4.0 relays come indefinite reverse polarity condition. On the in two varieties, uni-directional and bi- other hand, if the application requires the directional; understanding the differences relay to be connected between two sources, between the two is critical when choosing or, if between one source and one or more the proper device for any given application. loads, the load(s) is(aren’t) reverse polarity protected, then a bi-directional type must be The terms “uni-directional” and “bi- used; the fuse will still likely blow, but no directional” do not actually refer to the current will flow through the MOSFET ability of the MOSFET array to pass current array body diodes and the relay will survive when on, but rather its ability to block an indefinite reverse polarity condition (the current when off. The necessity for the two load(s) will also be protected). different types originates from a side effect of the MOSFET manufacturing process, COLD-CRANK TOLERANCE namely, the existence of the integral body diode and can be understood by examining The internal resistance of most batteries Figures 1 (uni-directional relay) and 2 (bi- increases as temperature decreases, which directional relay). can result in a very low terminal voltage under high current load conditions. Of In Figure 1, we can see that the MOSFET particular concern is the case of a 12 V array body diodes can be represented as a automotive cold-crank condition, where the single one with its anode at the load(s) and battery terminal voltage can fall to as low as the cathode at the source. As long as 1) the 3 V for 15 ms. While much equipment can source is not connected backwards, 2) the be allowed to reset during this low-voltage load terminal is guaranteed never to go 0.3 condition, other electronics such as safety V higher (referenced to the relay’s ground equipment must continue to operate terminal) than the source terminal, and 3) throughout the entire cranking process (this the relay is not installed improperly (i.e. the situation has become more prevalent with source to the load and vice-a-versa), then no the popularity of hybrid vehicles that stop current will flow through the body diodes. and start an internal combustion engine If the source is connected reverse polarity, while the vehicle is in motion in order to then the situation arises described in the maximize fuel efficiency). “REVERSE POLARITY PROTECTION” section; if a voltage appears at the load If a POWER-GATE generation 4.0 relay is terminal higher than that on the source placed between a starting battery and critical terminal (plus 0.3 V) while the relay is loads, it must remain closed during a cold- “open”, then current will flow from the load crank condition. With that goal in mind, the to the source through the now forward- relays have been designed to operate biased body diodes causing them to heat up

February 20, 2018 Created by: Peter Srsic Perfect Switch L.L.C. 12 of 12 AS0705-R1 and, therefore, increasing the risk of MOSFET FAILURE MOSFET failure; if the relay is installed backwards, current will immediately begin Although great care has been taken during to flow from the source to the load through the design and testing phases of the the MOSFET body diodes with no way to POWER-GATE generation 4.0 relays to stop the flow. Consequently, the uni- maximize performance, while also directional relay can only be truly opened in documenting the relay’s limitations and one direction (from the source to the load bounds, we are also aware that an end-user terminal). may, intentionally or unintentionally, exceed the ratings of MOSFET array. If this excess In Figure 2 we can see that the MOSFET leads to failure of one or more of the array body diodes can be represented as two MOSFETs in the array, it is important to be single ones in a back-to-back, common aware of the fact that the general failure anode configuration, with the cathodes mode of MOSFETs is the shorted state. It is connected to the two power terminals. Due possible for MOSFETs to fail open, but this to this arrangement, a reverse polarity will usually only occur under extremely high condition on one or both terminals will not currents where the internal wire bonds from cause current to flow through the body the MOSFET substrate to the package’s lead diodes since one is always reverse-biased frame actually blow open. Under most (although the fuse will likely blow). practical conditions outside the allowable Additionally, this arrangement is truly open operating parameters outlined in the uni- and in both directions when the MOSFET array bi-directional specification sheets, the user is open, since, again, one body diode will should assume that if one or more always be reverse-biased regardless of the MOSFETs were to fail, they will fail voltage polarity between the two power shorted. terminals. REVISION HISTORY DECISION TREE: The following decision tree will assist in deciding whether any Rev 1: Original release (2/20/18) particular application requires a uni- or bi- directional relay.

Figure 3: Uni- or Bi-directional Decision Tree

February 20, 2018 Created by: Peter Srsic