MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits General Description Features The MAX16128/MAX16129 load-dump/reverse-voltage protection circuits protect power supplies from damaging input-voltage conditions, including overvoltage, reverse-voltage, and high-voltage transient pulses. Using a built-in charge pump, the devices control two external back-to-back n-channel MOSFETs that turn off and isolate downstream power supplies during damaging input conditions, such as an automotive load-dump pulse or a reverse-battery condition. Operation is guaranteed down to 3V that ensures proper operation during automotive cold-crank conditions. These devices feature a flag output (FLAG) that asserts during fault conditions. SOperates Down to +3V, Riding Out Cold-Crank Conditions For reverse-voltage protection, external back-to-back MOSFETs outperform the traditional reverse-battery diode, minimizing the voltage drop and power dissipation during normal operation. SInternal Charge-Pump Circuit Enhances External n-Channel MOSFET The devices use fixed overvoltage and undervoltage thresholds, minimizing the external component count. The MAX16129 provides limiter-mode fault management for overvoltage and thermal-shutdown conditions; whereas the MAX16128 provides switch-mode fault management for overvoltage and thermal shutdown conditions. In the limiter mode, the output voltage is limited and FLAG is asserted low during a fault. In the switch mode, the external MOSFETs are switched off and FLAG is asserted low after a fault. The switch mode is available in four options—Latch mode, 1 Autoretry mode, 3 Autoretry mode, and Always autoretry mode. S-36V to +90V Wide Input-Voltage Protection Range SMinimal Operating Voltage Drop Reverse-Voltage Protection SFast Gate Shutoff During Fault Conditions with Complete Load Isolation SFixed Undervoltage/Overvoltage Thresholds SThermal Shutdown Protection SLow Supply Current and Low Shutdown Current SFLAG Output Identifies Fault Condition SAutomotive Qualified S-40NC to +125NC Operating Temperature Range SAvailable in 3mm x 3mm, 8-Pin µMAX Package Ordering Information appears at end of data sheet. The MAX16128/MAX16129 are available in an 8-pin FMAXM package and operate over the automotive temperature range (-40NC to +125NC). Applications Automotive Industrial Avionics Telecom/Server/Networking µMAX is a registered trademark of Maxim Integrated Products, Inc. For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maximintegrated.com. 19-6146; Rev 1; 9/12 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits ABSOLUTE MAXIMUM RATINGS (All pins referenced to GND.) IN.............................................................................-36V to +90V SHDN.............................................-0.3V to max (0V, VIN + 0.3V) SRC, GATE..............................................................-36V to +45V SRC to GATE...........................................................-36V to +30V OUT........................................................................-0.3V to +45V FLAG......................................................................-0.3V to +45V Continuous Sink/Source (all pins).................................. Q100mA Continuous Power Dissipation (TA = +70NC) (multilayer board) FMAX (derate 12.9mW/NC above +70NC)...............1030.9mW Operating Temperature Range......................... -40NC to +125NC Junction Temperature......................................................+150NC Storage Temperature Range............................. -60NC to +150NC Lead Temperature (soldering, 10s).................................+300NC Soldering Temperature (reflow).......................................+260NC Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to absolute maximum rating conditions for extended periods may affect device reliability. PACKAGE THERMAL CHARACTERISTICS (Note 1) FMAX Junction-to-Ambient Thermal Resistance (BJA)........77.6NC/W Junction-to-Case Thermal Resistance (BJC)..................5NC/W Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a four-layer board. For detailed information on package thermal considerations, refer to www.maximintegrated.com/thermal-tutorial. ELECTRICAL CHARACTERISTICS (VIN = 12V, CGATE-SOURCE = 1nF, TA = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER Input Voltage Range SYMBOL VIN CONDITIONS 3 30 -36 +90 VIN = VSRC = VIN = 12V 224 320 VIN = VSRC = VIN = 30V 260 380 VIN = VSRC = VIN = 12V 34 50 VIN = VSRC = VIN = 30V 64 100 VIN = VSRC = 12V 36 200 VIN = VSRC = 30V 240 350 VUV 1.03 x VUV IIN ISRC Internal Undervoltage Threshold VUV_TH Internal Undervoltage-Threshold Hysteresis VUV_HYS Internal Overvoltage Threshold VOV_TH Internal Overvoltage-Threshold Hysteresis VOV_HYS Maxim Integrated MAX Protection range SHDN = low SRC Input Current TYP Operating range SHDN = high Input Supply Current MIN VIN rising V FA 0.97 x VUV 0.05 x VUV VIN rising UNITS 0.97 x VOV VOV 0.05 x VOV FA V V 1.03 x VOV V V 2 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits ELECTRICAL CHARACTERISTICS (continued) (VIN = 12V, CGATE-SOURCE = 1nF, TA = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER Internal Cold-Crank Threshold SYMBOL VCCK CONDITIONS VIN falling MIN TYP MAX UNITS 0.97 x VCCK VCCK 1.03 x VCCK V 0.05 x VCCK Internal Cold-Crank Threshold Hysteresis VCCK_HYS MAX16128 4 MAX16129 2 V OUT Input Resistance to Ground ROUT POK Threshold Rising VPOK+ 0.9 x VIN V POK Threshold Falling VPOK- 0.87 x VIN V Startup Response Time tSTART Autoretry Timeout tRETRY GATE Rise Time (Note 3) mI 150 Fs 150 ms tRISE VGATE rising (GND to VSRC + 8V) 1 ms Overvoltage-to-GATE Propagation Delay tOVG VIN rising (MAX16128) from (0.9 x VOV_TH) to (1.1 x VOV_TH), VOUT rising (MAX16129) from (0.9 x VOV_TH) to (1.1 x VOV_TH) 1 Fs Undervoltage-to-GATE Propagation Delay tUVG VIN falling from (1.1 x VUV_TH) to (0.9 x VUV_TH) 21 Fs tOV VIN rising (MAX16128) from (0.9 x VOV_TH) to (1.1 x VOV_TH) VOUT rising (MAX16129) from (0.9 x VOV_TH) to (1.1 x VOV_TH) 1 Fs Overvoltage to FLAG Propagation Delay GATE Output Voltage High Above VSRC GATE Pulldown Current GATE Charge-Pump Current VGS IPD IGATE VIN = VSRC = VOUT = 3V, IGATE = -1FA 5 5 5.5 VIN = VSRC = VOUT = 12V, IGATE = -1FA 8 9 10 VIN = VSRC = VOUT = 24V, IGATE = -1FA 7 8.5 10 VIN = VSRC = VOUT = 30V, IGATE = -1FA 6.25 8 9.5 VGATE = 12V 8.8 mA VIN = VGATE = VSRC = 12V 180 FA V Thermal Shutdown T+ +145 NC Thermal-Shutdown Hysteresis δT 15 NC SHDN Logic-High Input Voltage VIH SHDN Logic-Low Input Voltage VIL Maxim Integrated 1.4 V 0.4 V 3 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits ELECTRICAL CHARACTERISTICS (continued) (VIN = 12V, CGATE-SOURCE = 1nF, TA = -40NC to +125NC, unless otherwise noted. Typical values are at TA = +25NC.) (Note 2) PARAMETER SYMBOL SHDN Input Pulse Width tPW SHDN Input Pulldown Current ISPD FLAG Output Voltage Low VOL MIN TYP MAX UNITS 6 Fs 0.8 IIL FLAG Leakage Current CONDITIONS 1.2 FA FLAG sinking 1mA 0.4 V VFLAG = 12V 0.5 FA Note 2: All parameters are production tested at TA = +25NC. Limits over the operating temperature range are guaranteed by design and characterization. Note 3: The MAX16128/MAX16129 power up with the external MOSFETs in off mode (VGATE = VSRC). The external MOSFETs turn on tSTART after the devices are powered up and all input conditions are valid. Typical Operating Characteristics (VIN = 12V, TA = +25NC, unless otherwise noted.) 150 100 SHDN = HIGH GATE ENHANCED 290 270 250 230 210 190 23 33 0 20 40 60 80 100 120 TEMPERATURE (°C) 35 30 25 20 15 9 15 21 27 1.0 0.8 0.7 0.6 0.5 0.4 0.3 0.2 0.1 10 Maxim Integrated 3 0.9 SHDN PULLDOWN CURRENT (µA) 40 40 SHDN PULLDOWN CURRENT vs. TEMPERATURE MAX16128/29 toc04 SUPPLY CURRENT (µA) SHDN = LOW 50 SUPPLY VOLTAGE (V) SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE 45 60 10 -40 -20 SUPPLY VOLTAGE (V) 50 70 MAX16128/29 toc05 13 SHDN = LOW 80 20 150 3 90 30 170 50 100 SUPPLY CURRENT (µA) 200 310 MAX16128/29 toc02 SHDN = HIGH GATE ENHANCED SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) MAX16128/29 toc01 300 250 SHUTDOWN SUPPLY CURENT vs. SUPPLY VOLTAGE SUPPLY CURRENT vs. TEMPERATURE MAX16128/29 toc03 SUPPLY CURRENT vs. SUPPLY VOLTAGE 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) TEMPERATURE (°C) 4 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Typical Operating Characteristics (continued) (VIN = 12V, TA = +25NC, unless otherwise noted.) 6 5 4 3 8.8 8.4 8.0 7.6 7.2 2 6.8 1 6.4 VIN = VSRC = VOUT = 12V GATE ENHANCED 6.0 0 10 15 20 25 30 35 TEMPERATURE (°C) INTERNAL OVERVOLTAGE THRESHOLD vs. TEMPERATURE 140 120 100 80 60 40 VIN = VGATE = VSRC GATE ENHANCED 20 25 100 RISING 98 96 94 FALLING 92 90 -40 -25 -10 5 20 35 50 65 80 95 110 125 VIN (V) TEMPERATURE (°C) INTERNAL UNDERVOLTAGE THRESHOLD vs. TEMPERATURE FLAG OUTPUT LOW VOLTAGE vs. CURRENT 0.5 102 100 RISING 96 0.4 FLAG VOLTAGE (V) 104 98 102 30 MAX16128/29 toc10B INTERNAL UNDERVOLTAGE THRESHOLD (%VUV) 15 INTERNAL OVERVOLTAGE THRESHOLD (%VOV) MAX16128/29 toc09 GATE PULL-UP CURRENT (µA) 160 10 8 -40 -25 -10 5 20 35 50 65 80 95 110 125 180 5 11 TEMPERATURE (°C) 200 0 14 5 GATE PULLUP CURRENT vs. VIN 0 17 -40 -25 -10 5 20 35 50 65 80 95 110 125 VIN (V) 20 VGATE = 12V MAX16128/29 toc11 5 MAX16128/29 toc08 9.2 20 MAX16128/29 toc10A 7 9.6 GATE PULLDOWN CURRENT (mA) 8 10.0 MAX16128/29 toc07 GATE-TO-SRC VOLTAGE (V) 9 GATE-TO-SRC VOLTAGE (V) MAX16128/29 toc06 10 0 GATE PULLDOWN CURRENT vs. TEMPERATURE GATE-TO-SRC VOLTAGE vs. TEMPERATURE GATE-TO-SRC VOLTAGE vs. VIN 0.3 0.2 94 92 FALLING 90 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) Maxim Integrated 0.1 0 0.5 1.0 1.5 2.0 FLAG CURRENT (mA) 5 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Typical Operating Characteristics (continued) (VIN = 12V, TA = +25NC, unless otherwise noted.) REVERSE CURRENT vs. REVERSE VOLTAGE OVERVOLTAGE FAULT-TO-GATE PROPAGATION DELAY vs. TEMPERATURE 25 REVERSE CURRENT (µA) 1.8 MAX16128/29 toc13 30 MAX16128/29 toc12 PROPAGATION DELAY (µs) 2.0 1.6 1.4 1.2 20 15 10 5 0 1.0 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 5 10 15 20 25 TEMPERATURE (°C) REVERSE VOLTAGE (V) STARTUP WAVEFORM (VIN PULSED O TO 12V, RLOAD = 100I, CIN = 0.1µF, COUT = 10µF) STARTUP FROM SHUTDOWN (SHDN) RISING FROM O TO 2V, VIN = 12V, RLOAD = 100I, CIN = 0.1µF MAX16128/29 toc14 30 MAX16128/29 toc15 VIN 10V/div VSHDN 2V/div VGATE 10V/div VGATE 10V/div VOUT 10V/div VOUT 10V/div 200µs/div 400µs/div OVERVOLTAGE SWITCH FAULT (VOV = 21V, CIN = 0.1µF, COUT = 10µF) OVERVOLTAGE LIMITER (VOV = 21V, CIN = 0.1µF, COUT = 10µF) MAX16128/29 toc16 MAX16128/29 toc17 VIN 20V/div VIN 20V/div VGATE 20V/div VOUT 10V/div VGATE 10V/div VOUT 10V/div 20ms/div Maxim Integrated 20ms/div 6 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Pin Configuration TOP VIEW OUT 1 SRC 2 GATE 3 IN 4 + MAX16128 MAX16129 8 FLAG 7 I.C. 6 GND 5 SHDN µMAX Pin Description PIN NAME FUNCTION 1 OUT Output Voltage-Sense Input. Connect OUT to the load with a 100I series resistor. Bypass with a minimum 10FF capacitor to GND. 2 SRC Source Input. Connect SRC to the common source connection of the external MOSFETs. When the MOSFETs are turned off, this connection is clamped to GND. An external zener diode between SRC and GATE protects the gates of the external MOSFETs. 3 GATE Gate-Driver Output. Connect GATE to the gates of the external n-channel MOSFETs. GATE is the chargepump output during normal operation. GATE is quickly pulled low during a fault condition or when SHDN is pulled low. 4 IN Positive Supply Input Voltage. Connect IN to the positive side of the input voltage. Bypass IN with a 0.1FF ceramic capacitor to GND. 5 SHDN Shutdown Input. Drive SHDN low to force GATE and FLAG low and turn off the external n-channel MOSFETs. Connect a 100kI resistor from SHDN to IN for normal operation. 6 GND Ground 7 I.C. 8 FLAG Maxim Integrated Internally connected to GND FLAG Output. During startup, FLAG is low as long as VOUT is lower than 90% of VIN and after that it is high impedance. It asserts low during shutdown mode, an overvoltage, thermal shutdown, or undervoltage fault or when VOUT falls below 90% of VIN. FLAG asserts low during a cold-crank fault to signal reverse-current protection. 7 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Detailed Description The MAX16128/MAX16129 transient protection circuits are suitable for automotive and industrial applications where high-voltage transients are commonly present on supply voltage inputs. The devices monitor the input voltage and control two external common-source n-channel MOSFETs to protect downstream voltage regulators during loaddump events or other automotive pulse conditions. The devices feature an overvoltage and an undervoltage comparator for voltage window detection. A flag output (FLAG) asserts when a fault event occurs. Two external back-to-back n-channel MOSFETs provide reverse-voltage protection and also prevent reverse current during a fault condition. Compared to a traditional reverse-battery diode, this approach minimizes power dissipation and voltage drop. The MAX16129 provides a limiter-mode fault management for overvoltage and thermal-shutdown conditions, whereas the MAX16128 provides switch-mode fault management for overvoltage and thermal-shutdown conditions. In the limiter mode, the MOSFETs cycle on and off so the output voltage is limited. In the switch mode, the external MOSFETs are switched off, disconnecting the load from the input. In both cases, FLAG asserts to indicate a fault. Gate Charge Pump The devices use a charge pump to generate the GATE to SRC voltage and enhance the external MOSFETs. After the input voltage exceeds the input undervoltage threshold, the charge pump turns on after a 150Fs delay. During a fault condition, GATE is pulled to ground with an 8.8mA (min) pulldown current. Note that an external zener diode is required to be connected between the gate and source of the external MOSFETs (see the Applications Information section). Overvoltage Protection The devices detect overvoltage conditions using a comparator that is connected through an internal resistive divider to the input or output voltage. An overvoltage condition causes the GATE output to go low, turning off the external MOSFETs. FLAG also asserts to indicate the fault condition. Maxim Integrated Overvoltage Limiter (MAX16129) In overvoltage-limiter mode, the output voltage is regulated at the overvoltage-threshold voltage and continues to supply power to downstream devices. In this mode, the device operates like a voltage regulator. During normal operation, GATE is enhanced 9V above SRC. The output voltage is monitored through an internal resistive divider. When OUT rises above the overvoltage threshold, GATE goes low and the MOSFETs turn off. As the voltage on OUT falls below the overvoltage threshold minus the threshold hysteresis, GATE goes high and the MOSFETs turn back on again, regulating OUT in a switched-linear mode at the overvoltage threshold. The switching frequency depends on the gate charge of the MOSFETs, the charge-pump current, the output load current, and the output capacitance. Caution must be exercised when operating the MAX16129 in voltage-limiting mode for long durations. Since MOSFETs can dissipate power continuously during this interval, proper heatsinking should be implemented to prevent damage to them. Overvoltage Switch (MAX16128) In the overvoltage switch mode, the internal overvoltage comparator monitors the input voltage and the load is completely disconnected from the input during an overvoltage event. When the input voltage exceeds the overvoltage threshold, GATE goes low and the MOSFETs turn off, disconnecting the input from the load. After that, for the autoretry-mode version, the autoretry timer starts, while for the latched-mode version a power cycle to IN or a cycle on SHDN is needed to turn the external MOSFETs back on. The MAX16128 can be configured to latch off (suffix D) even after the overvoltage condition ends. The latch is cleared by cycling IN below the undervoltage threshold or by toggling SHDN. The devices can also be configured to retry: U One time, then latch off (suffix B) U Three times, then latch off (suffix C) U Always retry and never latch off (suffix A) There is a fixed 150ms (typ) delay between each retry attempt. If the overvoltage-fault condition is gone when a retry is attempted, GATE goes high and power is restored to the downstream circuitry. 8 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Undervoltage Protection The devices monitor the input voltage for undervoltage conditions. If the input voltage is below the undervoltage threshold (VIN < VUV-TH - VUV-HYS), GATE goes low, turning off the external MOSFETs and FLAG asserts. When the input voltage exceeds the undervoltage threshold (VIN > VUV_TH), GATE goes high after a 150Fs delay (typ). For the MAX16128/MAX16129, the undervoltage threshold is determined by the part number suffix option (see Table 2). Cold-Crank Monitoring Cold-crank faults occur when the input voltage decreases from its steady-state condition. A cold-crank comparator monitors IN through an internal resistive divider. The MAX16128/MAX16129 offer two ways to handle this kind of fault depending on a part number suffix (see the Selector Guide): • The cold-crank comparator is disabled and external MOSFETs stay on during the falling input-voltage transient unless the input voltage falls below the undervoltage threshold (see Table 2). • The cold-crank comparator is enabled and external MOSFETs are switched off by pulling down GATE if the input voltage falls below the cold-crank threshold to avoid load discharge due to reverse current from OUT to IN (see Table 4). In the last case, cold-crank protection is enabled as long as VOUT is higher than 90% of VIN (with a 3% hysteresis) and VIN is higher than the undervoltage threshold. When the monitored input voltage falls below the falling coldcrank fault threshold (VIN < VCCK), the GATE is pulled down and FLAG is asserted low. When the input voltage rises back above the rising cold-crank fault threshold (VIN > VCCK + VCLK_HYS), FLAG is released and the charge pump enhances GATE above SRC, reconnecting the load to the input. Thermal Shutdown The devices’ thermal-shutdown feature turns off the MOSFETs if the internal die temperature exceeds 145NC (TJ). By ensuring good thermal coupling between the MOSFETs and the devices, the thermal shutdown can turn off the MOSFETs if they overheat. When the junction temperature exceeds TJ = +145NC (typ), the internal thermal sensor signals the shutdown logic, pulling the GATE voltage low and allowing the device to cool. When TJ drops by 15NC (typ), GATE goes Maxim Integrated high and the MOSFETs turn back on. Do not exceed the absolute maximum junction-temperature rating of TJ = +150NC. Flag Output (FLAG) An open-drain FLAG output indicates fault conditions. During startup, FLAG is initially low and goes high impedance when VOUT is greater than 90% of VIN if no fault conditions are present. FLAG asserts low during shutdown mode, an overvoltage, thermal shutdown, or undervoltage fault, or when VOUT falls below 90% of VIN. In the versions where the cold-crank comparator is enabled, FLAG asserts low during a cold-crank fault. Reverse-Voltage Protection The devices integrate reverse-voltage protection, preventing damage to the downstream circuitry caused by battery reversal or negative transients. The devices can withstand reverse voltage to -6V without damage to themselves or the load. During a reverse-voltage condition, the two external n-channel MOSFETs are turned off, protecting the load. Connect a 0.1FF ceramic capacitor from IN to GND, connect a 10nF ceramic capacitor from GATE to SRC, connect a 10FF capacitor from OUT to GND, and minimize the parasitic capacitance from GATE to GND to have fast reverse-battery voltage-transient protection. During normal operation, both MOSFETs are turned on and have a minimal forward-voltage drop, providing lower power dissipation and a much lower voltage drop than a reverse-battery protection diode. Applications Information Automotive Electrical Transients (Load Dump) Automotive circuits generally require supply voltage protection from various transient conditions that occur in automotive systems. Several standards define various pulses that can occur. Table 1 summarizes the pulses from the ISO 7637-2 specification: Most of the pulses can be mitigated with capacitors and zener clamp diodes (see the Typical Operating Characteristics and also the Increasing the Operating Voltage Range section). The load dump (pulse 5a and 5b) occurs when the alternator is charging the battery and a battery terminal gets disconnected. Due to the sudden change in load, the alternator goes out of regulation and the bus voltage spikes. The pulse has a rise time of about 10ms and a fall time of about 400ms but can extend out to 1s or more depending on the characteris 9 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Table 1. Summary of ISO 7637-2 Pulses NAME DESCRIPTION Pulse 1 Inductive load disconnection Pulse 2a Inductive wiring disconnection Pulse 3a Pulse 3b PEAK VOLTAGE (V) (max)* DURATION 12V SYSTEM -100 1 to 2ms 50 0.05ms -150 Switching transients 0.2Fs 100 -7 100ms (initial) -6 Up to 20s Pulse 4 Cold crank Pulse 5a Load dump (unsuppressed) 87 Pulse 5b Load dump (suppressed) (Varies, but less than pulse 5a) 400ms (single) *Relative to system voltage tics of the charging system. The magnitude of the pulse depends on the bus voltage and whether the system is unsuppressed or uses central load-dump suppression (generally implemented using very large clamp diodes built into the alternator). Table 1 lists the worst-case values from the ISO 7637-2 specification. Cold crank (pulse 4) occurs when activating the starter motor in cold weather with a marginal battery. Due to the large load imposed by the starter motor, the bus voltage sags. Since the devices can operate down to 3V, the downstream circuitry can continue to operate through a cold-crank condition. If desired, the undervoltage threshold can be increased so that the MOSFETs turn off during a cold crank, disconnecting the downstream circuitry. An output reservoir capacitor can be connected from OUT to GND to provide energy to the circuit during the coldcrank condition. Refer to the ISO 7637-2 specification for details on pulse waveforms, test conditions, and test fixtures. MOSFET Selection MOSFET selection is critical to design a proper protection circuit. Several factors must be taken into account: the gate capacitance, the drain-to-source voltage rating, the on-resistance (RDS(ON)), the peak power-dissipation capability, and the average power-dissipation limit. In general, both MOSFETs should have the same part number. For size-constrained applications, a dual MOSFET can save board area. Select the drain-to-source voltage so that the MOSFETs can handle the highest voltage that might be applied to the circuit. Gate capacitance is not as critical but it does determine the maximum turn-on Maxim Integrated and turn-off time. MOSFETs with more gate capacitance tend to respond more slowly. MOSFET Power Dissipation The RDS(ON) must be low enough to limit the MOSFET power dissipation during normal operation. Power dissipation (per MOSFET) during normal operation can be calculated using this formula: P = ILOAD2 x RDS(ON) where P is the power dissipated in each MOSFET and ILOAD is the average load current. During a fault condition in switch mode, the MOSFETs turn off and do not dissipate power. Limiter mode imposes the worst-case power dissipation. The average power can be computed using the following formula: P = ILOAD x (VIN - VOUT) where P is the average power dissipated in both MOSFETs, ILOAD is the average load current, VIN is the input voltage, and VOUT is the average limited voltage on the output. In limiter mode, the output voltage is a sawtooth wave with characteristics determined by the RDS(ON) of the MOSFETs, the output load current, the output capacitance, the gate charge of the MOSFETs, and the GATE charge-pump current. Since limiter mode can involve high switching currents when the GATE is turning on at the start of a limiting cycle (especially when the output capacitance is high), it is important to ensure the circuit does not violate the peak power rating of the MOSFETs. Check the pulse power ratings in the MOSFET data sheet. MOSFET Gate Protection 10 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits To protect the gate of the MOSFETs, connect a zener clamp diode from the gate to the source. The cathode connects to the gate, and the anode connects to the source. Choose the zener clamp voltage to be above 10V and below the MOSFET VGS maximum rating. It is important to compute the peak power dissipation in the series resistor. Most standard surface-mount resistors are not able to withstand the peak power dissipation during certain pulse events. Check the resistor data sheets for pulse-power derating curves. If necessary, connect multiple resistors in parallel or use automotiverated resistors. Increasing the Operating Voltage Range The devices can tolerate -36V to +90V. To increase the positive input-voltage protection range, connect two back-to-back zener diodes from IN to GND, and connect a resistor in series with IN and the power-supply input to limit the current drawn by the zener diodes (see Figure 1). The shutdown input needs a series resistor to limit the current if VIN exceeds the clamped voltage on IN. A good starting point is 100kI. Output Reservoir Capacitor The output capacitor can be used as a reservoir capacitor to allow downstream circuitry to “ride out” fault transient conditions. Since the voltage at the output is protected from input-voltage transients, the capacitor voltage rating can be less than the expected maximum input voltage. Zener diode D1 clamps positive voltage excursions and D2 clamps negative voltage excursions. Set the zener voltages so the worst-case voltages do not exceed the ratings of the part. Also ensure that the zener diode power ratings are not exceeded. The combination of the series resistor and the zener diodes also help snub pulses on the supply voltage input and can aid in clamping the low-energy ISO 7637-2 pulses. DC-DC CONVERTER VBATT IN 10nF R3 10µF 100I OUT GND R3 GATE SRC OUT IN D1 100kI SHDN D2 100nF MAX16128 MAX16129 FLAG GND Figure 1. Circuit to Increase Input-Voltage Protection Range Maxim Integrated 11 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Typical Operating Circuit VIN VOUT 10nF GATE 100I SRC 10µF COUT OUT IN 100nF 100kI SHDN MAX16128 MAX16129 FLAG GND Figure 2. MAX16128/MAX16129 Typical Operating Circuit Maxim Integrated 12 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Functional Diagram GATE SRC OUT CHARGE PUMP MAX16128 MAX16129 IN UV POWEROK 1.225V OV CCK 1.225V 1.225V CONTROL LOGIC FLAG THERMAL PROTECTION SHDN GND Figure 3. MAX16128/MAX16129 Functional Diagram Maxim Integrated 13 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Table 2. UV Threshold (V) (First Suffix) Table 4. CCK Threshold (Third Suffix) PART SUFFIX UV THRESHOLD (TYP) (V) PART SUFFIX CCK THRESHOLD (TYP) (V) A 3 A No CCK B 5 B 5.64 C 5.98 C 7.65 D 7.03 D 9.67 E 8.13 F 9.09 G 10.3 Table 3. OV Threshold (V) (Second Suffix) PART SUFFIX OV THRESHOLD (TYP) (V) A 13.64 B 15 C 18.6 D 20.93 E 24.16 F 28.66 G 31.62 Table 5. Switch Mode Option (MAX16128 Only) PART SUFFIX SWITCH MODE A Always autoretry B One retry, then latch C Three retries, then latch D Latch mode Selector Guide PART PINPACKAGE TOP MARK FUNCTION MAX16128AUAACAC+ 8 FMAX +AACE Switch Mode MAX16129AUAEBD+ 8 FMAX +AACG Limiter Mode Ordering Information TEMP RANGE PIN-PACKAGE FUNCTION MAX16128AUA_ _ _ _+ PART -40°C to +125°C 8 FMAX Switch Mode MAX16129AUA_ _ _+ -40°C to +125°C 8 FMAX Limiter Mode Note: The first “_” is a placeholder for the undervoltage threshold. A desired undervoltage threshold is set by the letter suffix found in Table 2. The second “_” is a placeholder for the overvoltage threshold. A desired overvoltage threshold is set by the letter suffix found in Table 3. The third “_” is a placeholder for the CCK threshold set by the letter suffix found in Table 4. For MAX16128 options, the fourth “_” is a placeholder for the switch-mode option. A desired switch mode is set by the letter suffix found in Table 5. +Denotes a lead(Pb)-free/RoHS-compliant package. Chip Information PROCESS: BiCMOS Maxim Integrated Package Information For the latest package outline information and land patterns (footprints), go to www.maximintegrated.com/packages. Note that a “+”, “#”, or “-” in the package code indicates RoHS status only. Package drawings may show a different suffix character, but the drawing pertains to the package regardless of RoHS status. PACKAGE TYPE PACKAGE CODE OUTLINE NO. LAND PATTERN NO. 8 FMAX U8+1 21-0036 90-0092 14 MAX16128/MAX16129 Load-Dump/Reverse-Voltage Protection Circuits Revision History REVISION NUMBER REVISION DATE 0 12/11 Initial release 1 9/12 Updated the Features, Electrical Characteristics, Typical Operating Characteristics, Cold-Crank Monitoring, Increasing the Operating Voltage Range sections, and Tables 3 and 4 DESCRIPTION PAGES CHANGED — 1–5, 9, 11, 14 Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are implied. Maxim reserves the right to change the circuitry and specifications without notice at any time. The parametric values (min and max limits) shown in the Electrical Characteristics table are guaranteed. Other parametric values quoted in this data sheet are provided for guidance. Maxim Integrated 160 Rio Robles, San Jose, CA 95134 USA 1-408-601-1000 © 2012 Maxim Integrated 15 The Maxim logo and Maxim Integrated are trademarks of Maxim Integrated Products, Inc.