19-6053; Rev 0; 11/11 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits General Description Benefits and Features The MAX16126/MAX16127 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 to ensure 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. SCharge-Pump Circuit Enhances External n-Channel MOSFETs The MAX16126/MAX16127 use external resistors to adjust the overvoltage and undervoltage comparator thresholds for maximum flexibility. The MAX16127 provides limiter-mode fault management for overvoltage and thermal shutdown conditions; whereas the MAX16126 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. The MAX16126/MAX16127 are available in 12-pin TQFN packages. These devices operate over the automotive temperature range (-40NC to +125NC). S-30V to +90V Wide Input Voltage Protection Range SMinimal Operating Voltage Drop Reverse-Voltage Protection SFast Gate Shutoff During Fault Conditions with Complete Load Isolation SAdjustable 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, 12-Pin TQFN Package Ordering Information appears at end of data sheet. For related parts and recommended products to use with this part, refer to www.maxim-ic.com/MAX16126.related. Applications Automotive Industrial Avionics Telecom/Server/Networking ����������������������������������������������������������������� Maxim Integrated Products 1 For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com. MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits ABSOLUTE MAXIMUM RATINGS (All pins referenced to GND.) IN.............................................................................-30V to +90V SHDN.............................................-0.3V to max (0V, VIN + 0.3V) TERM.............................................-0.3V to max (0V, VIN + 0.3V) SRC, GATE..............................................................-30V to +45V SRC to GATE...........................................................-30V to +30V OUT........................................................................-0.3V to +45V FLAG......................................................................-0.3V to +45V OVSET, UVSET.........................................................-0.3V to +6V Continuous Sink/Source (all pins).................................. Q100mA Continuous Power Dissipation (TA = +70NC) (multilayer board) TQFN (derate 14.7mW/NC above +70NC)...............1176.5mW 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) TQFN Junction-to-Ambient Thermal Resistance (BJA)...........68NC/W Junction-to-Case Thermal Resistance (BJC)................11NC/W Note 1: Package thermal resistances were obtained using the method described in JEDEC specification JESD51-7, using a fourlayer board. For detailed information on package thermal considerations, refer to www.maxim-ic.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 SYMBOL Input Voltage Range VIN Input Supply Current IIN SRC Input Current CONDITIONS MIN OVSET/UVSET Input Current OVSET/UVSET Threshold (Rising) OVSET/UVSET Threshold Hysteresis POK Threshold Rising VUVLO 24 Protection range -30 +90 SHDN = high 224 320 SHDN = low 34 50 75 110 VIN rising IUVSET/OVSET VTH MAX 3 ISRC IN Undervoltage Lockout TYP Operating range VIN rising 1.2 1.225 UNITS V FA FA 2.8 V 500 nA 1.25 V VTH-HYS 5 % VPOK+ V POK Threshold Falling VPOK- 0.9 x VIN 0.87 x VIN TERM On-Resistance RTERM 0.7 Startup Response Time tSTART Autoretry Timeout tRETRY GATE Rise Time tRISE VGATE rising (GND to VSRC + 6V) OVSET to GATE Propagation Delay tOVG VOVSET rising (VTH - 100mV to VTH + 100mV) UVSET to GATE Propagation Delay tUVG VUVSET rising (VTH - 100mV to VTH +100mV) (Note 3) V 1.2 kI 150 Fs 150 ms 1 ms 0.55 20 Fs Fs ����������������������������������������������������������������� Maxim Integrated Products 2 MAX16126/MAX16127 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 OVSET to FLAG Propagation Delay GATE Output Voltage High Above VSRC GATE Pulldown Current GATE Charge-Pump Current Thermal Shutdown SYMBOL tOV VOHGATE IPD IGATE CONDITIONS MIN VOVSET rising (VTH - 100mV to VTH + 100mV) δT SHDN Logic-High Input Voltage VIH SHDN Logic-Low Input Voltage VIL SHDN Input Pulse Width tPW SHDN Input Pulldown Current ISPD FLAG Output Voltage Low VOL FLAG Leakage Current IIL MAX 0.3 UNITS Fs VIN = VSRC = VOUT = 3V, IGATE = -1FA 4.3 4.7 6 VIN = VSRC = VOUT = 12V, IGATE = -1FA 6.25 7 8 VGATE = 12V 8.8 V VIN = VGATE = VSRC = 12V T+ Thermal Shutdown Hysteresis TYP mA 155 FA +145 NC 15 NC 1.4 V 0.4 6 V Fs 0.8 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. Note 3: The MAX16126/MAX16127 power up with the external MOSFETs in off mode (VGATE = VSRC). The external MOSFETs turn on tSTART after the IC is powered up and all input conditions are valid. ����������������������������������������������������������������� Maxim Integrated Products 3 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Typical Operating Characteristics (VIN = 12V, TA = +25NC, unless otherwise noted.) 150 100 270 100 250 230 210 190 10 20 30 60 80 30 25 20 1.0 0.9 0.8 6 12 18 24 10 0.7 9 8 0.6 0.5 0.4 0.3 7 6 5 4 0.2 3 2 0 TEMPERATURE (°C) TEMPERATURE (°C) 9 12 15 18 SUPPLY VOLTAGE (V) GATE-TO-SOURCE VOLTAGE vs. TEMPERATURE GATE PULLDOWN CURRENT vs. TEMPERATURE GATE PULLUP CURRENT vs. SUPPLY VOLTAGE 6.5 6.0 5.5 5.0 14 11 8 4.5 6 170 165 160 5 24 155 150 145 140 VIN = VGATE = VSRC GATE ENHANCED 135 4.0 21 MAX16126 toc09 17 VGATE = 12V VSRC = GND GATE PULLUP CURRENT (µA) 7.0 20 MAX16126 toc08 GATE ENHANCED VIN = VSRC = VOUT 3 -40 -25 -10 5 20 35 50 65 80 95 110 125 GATE PULLDOWN CURRENT (mA) 8.0 MAX16126 toc07 -40 -25 -10 5 20 35 50 65 80 95 110 125 30 GATE TO SOURCE VOLTAGE vs. SUPPLY VOLTAGE 0.1 10 40 SUPPLY VOLTAGE (V) (VGATE - VSRC) (V) 35 50 0 MAX16126 toc05 MAX16126 toc04 SHDN = LOW 60 10 100 120 SHDN PULLDOWN CURRENT vs. TEMPERATURE SHDN PULLDOWN CURRENT (µA) SUPPLY CURRENT (µA) 40 SHUTDOWN SUPPLY CURRENT vs. TEMPERATURE 15 (VGATE - VSRC) (V) 20 TEMPERATURE (°C) 40 7.5 0 SUPPLY VOLTAGE (V) 50 45 -40 -20 40 70 20 150 0 80 30 170 50 SHDN = LOW 90 MAX16126 toc06 200 SHDN = HIGH GATE ENHANCED SUPPLY CURRENT (µA) SUPPLY CURRENT (µA) 250 290 MAX16126 toc02 SHDN = HIGH GATE ENHANCED SUPPLY CURRENT (µA) 310 MAX16126 toc01 300 SHUTDOWN SUPPLY CURRENT vs. SUPPLY VOLTAGE SUPPLY CURRENT vs. TEMPERATURE MAX16126 toc03 SUPPLY CURRENT vs. SUPPLY VOLTAGE 130 -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) 0 5 10 15 20 25 30 SUPPLY VOLTAGE (V) ����������������������������������������������������������������� Maxim Integrated Products 4 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Typical Operating Characteristics (continued) (VIN = 12V, TA = +25NC, unless otherwise noted.) FALLING 0.9 MAX16126 toc10b RISING 1.3 0.7 0.5 0.4 FLAG VOLTAGE (V) 1.1 1.1 FALLING 0.9 0.7 0.5 0.3 0.2 0.1 0.5 -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) 0 0 30 25 REVERSE CURRENT (µA) 0.75 0.50 0.25 1.5 2.0 MAX16126 toc13 VOVSET PULSED FROM (VTH - 100mV) TO (VTH + 100mV) 1.0 REVERSE CURRENT vs. REVERSE VOLTAGE MAX16126 toc12 1.00 0.5 FLAG CURRENT (mA) OVERVOLTAGE FAULT TO GATE PROPAGATION DELAY vs. TEMPERATURE PROPAGATION DELAY (µs) OVSET THRESHOLD (V) 1.3 1.5 UVSET THRESHOLD (V) RISING MAX16126 toc10a 1.5 FLAG OUTPUT LOW VOLTAGE vs. CURRENT UVSET THRESHOLD vs. TEMPERATURE MAX16126 toc11 OVSET THRESHOLD vs. TEMPERATURE 20 15 10 5 0 0 -40 -25 -10 5 20 35 50 65 80 95 110 125 TEMPERATURE (°C) 0 5 10 15 20 25 30 REVERSE VOLTAGE (V) ����������������������������������������������������������������� Maxim Integrated Products 5 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Typical Operating Characteristics (continued) (VIN = 12V, TA = +25NC, unless otherwise noted.) STARTUP WAVEFORM (VIN = 0 TO 12V, RL = 100I, CIN = 0.1µF, COUT = 100µF) STARTUP FROM SHUTDOWN (SHDN RISING 0 TO 2V, VIN = 12V, RLOAD = 100I, CIN = 0.1µF) MAX16126 toc14 MAX16126 toc15 VIN 10V/div VSHDN 2V/div VGATE 10V/div VGATE 10V/div VOUT 10V/div VOUT 10V/div 400µs/div 400µs/div OVERVOLTAGE SWITCH FAULT (VOV = 20V, CIN = 0.1µF, COUT = 100µF) OVERVOLTAGE LIMITER (VUV = 4V, VOV = 20V, CIN = 0.1µF, COUT = 100µF) MAX16126 toc16 VIN 20V/div MAX16126 toc17 VIN 20V/div VGATE 20V/div VOUT 10V/div VGATE 10V/div VOUT 20V/div 100ms/div 20ms/div ����������������������������������������������������������������� Maxim Integrated Products 6 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits FLAG I.C. TOP VIEW OUT Pin Configuration 9 8 7 SRC 10 MAX16126 MAX16127 GATE 11 EP SHDN 1 2 3 N.C. + TERM IN 12 6 GND 5 OVSET 4 UVSET TQFN ����������������������������������������������������������������� Maxim Integrated Products 7 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Pin Description PIN NAME FUNCTION 1 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. 2 TERM Voltage-Divider Termination Output. TERM is internally connected to IN. TERM is high impedance when SHDN is low, forcing the current to zero in the resistive-divider connected to TERM. 3 N.C. 4 UVSET Undervoltage Threshold Adjustment Input. Connect UVSET to the external resistive voltage-divider network to adjust the desired input undervoltage threshold. Connect the resistive divider to TERM. 5 OVSET Overvoltage Threshold Adjustment Input. Connect OVSET to an external resistive voltage-divider network to adjust the desired overvoltage disable or overvoltage limit threshold. Connect the resistive divider to TERM for overvoltage switch-mode applications or to OUT for overvoltage limiting applications. 6 GND 7 I.C. 8 FLAG 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. 9 OUT Output Voltage-Sense Input. Connect OUT to the load with a 100I series resistor. Bypass with a minimum 10FF capacitor to GND. 10 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. 11 GATE Gate-Driver Output. Connect GATE to the gates of the external n-channel MOSFETs. GATE is the charge-pump output during normal operation. GATE is quickly pulled low during a fault condition or when SHDN is pulled low. 12 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. — EP Exposed Pad. Can be connected to GND or left unconnected. No Connection. Not internally connected. Ground Internally Connected. Connect to GND. ����������������������������������������������������������������� Maxim Integrated Products 8 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Detailed Description The MAX16126/MAX16127 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, and allows the circuit to operate at very low cold-crank voltages (3V minimum). The MAX16127 provides a limiter-mode fault management for overvoltage and thermal shutdown conditions, whereas the MAX16126 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 MAX16126/MAX16127 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 a 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 MAX16126/MAX16127 detect overvoltage conditions using a comparator that is connected through an external 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. Overvoltage Limiter (MAX16127) 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 7V above SRC. The output voltage is monitored through a resistive divider between OUT and OVSET. 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 MAX16127 in voltage-limiting mode for long durations. Since MOSFETs can dissipate power continuously during this interval, proper heat sinking should be implemented to prevent damage to them. Overvoltage Switch (MAX16126) 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 MAX16126 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. ����������������������������������������������������������������� Maxim Integrated Products 9 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Undervoltage Protection The MAX16126/MAX16127 monitor the input voltage for undervoltage conditions. If the input voltage is below the undervoltage threshold (VIN < VTH - VTH-HYS), GATE goes low, turning off the external MOSFETs and FLAG asserts. When the input voltage exceeds the undervoltage threshold (VIN > VTH), GATE goes high after a 150Fs delay (typ). For the MAX16126/MAX16127, an external resistive divider connected between TERM, UVSET, and GND sets the undervoltage threshold (TERM is connected to IN when SHDN is high). Thermal Shutdown The MAX16126/MAX16127 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 MAX16126/ MAX16127, 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 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. TERM Connection The TERM connection has an internal switch to IN. In shutdown (SHDN = GND), this switch is open. By connecting the voltage threshold resistive divider to TERM instead of directly to IN, power dissipation in the resistive divider can be eliminated and the shutdown supply current reduced. Reverse-Voltage Protection The MAX16126/MAX16127 integrate reverse-voltage protection, preventing damage to the downstream circuitry caused by battery reversal or negative transients. The devices can withstand reverse voltage to -30V 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 0.1µF ceramic capacitor from IN to GND, connect a 10nF ceramic capacitor from GATE to SRC, connect 10µF from OUTPUT to GND, and minimize the parasitic capacitance from GATE to GND to have a fast reserve-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 ISO7637-2 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 characteristics 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 ISO7637-2 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 MAX16126/MAX16127 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 cold-crank condition. ���������������������������������������������������������������� Maxim Integrated Products 10 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Table 1. Summary of ISO7637 Pulses NAME DESCRIPTION Pulse 1 Inductive load disconnection Pulse 2a Inductive wiring disconnection Pulse 3a Pulse 3b PEAK VOLTAGE (V) (max)* 12V SYSTEM -100 1ms to 2ms 50 0.05ms -150 Switching transients DURATION 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. Refer to the ISO7637-2 specification for details on pulse waveforms, test conditions, and test fixtures. Setting Overvoltage and Undervoltage Thresholds (MAX16126) The MAX16126 uses an external resistive divider to set the overvoltage and undervoltage thresholds. The MAX16126 operates in switch mode in which the internal overvoltage comparator monitors the input voltage. It uses three resistors in a single resistive divider to set the undervoltage and overvoltage thresholds. The top of the resistive divider connects to TERM (see Figure 1). The MAX16126 includes internal undervoltage and overvoltage comparators for window detection. GATE is enhanced and the n-channel MOSFETs are on when the IN voltage is within the selected window. When the monitored voltage falls below the lower limit (VTRIPLOW) or exceeds the upper limit (VTRIPHIGH) of the window, the GATE voltage goes to GND, turning off the MOSFETs. The circuit in Figure 1 shows the MAX16126 enabling the DC-DC converter when the monitored voltage is in the selected window. The resistor values R1, R2, and R3 can be calculated as follows: R VTRIPHIGH = VTH TOTAL R3 where RTOTAL = R1 + R2 + R3, VTH is the 1.225V OVSET/ UVSET threshold, VTH-HYS is the hysteresis. Use the following steps to determine the values for R1, R2, and R3: 1) Choose a value for RTOTAL, the sum of R1, R2, and R3. 2) Calculate R3 based on RTOTAL and the desired upper trip point: V × R TOTAL R3 = TH VTRIPHIGH 3) Calculate R2 based on RTOTAL, R3, and the desired lower trip point: R2 = (VTH - VTH-HYS ) × R TOTAL - R3 VTRIPLOW 4) Calculate R1 based on RTOTAL, R2, and R3: R1 = R TOTAL - R2 - R3 R VTRIPLOW = (VTH - VTH-HYS ) TOTAL R2 R3 + ���������������������������������������������������������������� Maxim Integrated Products 11 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits VIN 10nF GATE 100I SRC 10µF DC-DC CONVERTER IN OUT GND OUT IN 100kI SHDN 0.1µF TERM MAX16126 FLAG R1 UVSET R2 OVSET R3 GND Figure 1. Overvoltage and Undervoltage Window Detector Circuit (MAX16126) Setting Overvoltage and Undervoltage Thresholds (MAX16127) The MAX16127 operates in limiter mode and uses separate resistive dividers to set the undervoltage and overvoltage thresholds. The top of the overvoltage divider connects to OUT and the top of the undervoltage divider connects to TERM (see Figure 2). Use the following formula to calculate R4: R = R4 VTH × TOTAL_OV VOV where RTOTAL_UV = R3 + R4, VTH is the 1.225V OVSET rising threshold and VOV is the desired overvoltage threshold. The falling threshold of VTH is 5% below the rising threshold. Similarly, to calculate the values of R1 and R2: R = R2 (VTH - VTH-HYS ) × TOTAL_UV VUV where RTOTAL_UV = R1 + R2, VTH is the 1.225V UVSET rising threshold, VTH-HYS is the hysteresis, and VUV is the desired undervoltage threshold. Use the nearest standard-value resistor that is less than the calculated value. A lower value for total resistance dissipates more power, but provides slightly better accuracy. 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 and turn-off time. MOSFETs with more gate capacitance tend to respond more slowly. ���������������������������������������������������������������� Maxim Integrated Products 12 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits DC-DC CONVERTER VIN IN 10µF 10nF OUT GND 100I 100kI IN GATE SRC OUT SHDN 0.1µF MAX16127 FLAG TERM R3 R1 OVSET UVSET R2 GND R4 Figure 2. Overvoltage and Undervoltage Limiter Protection Configuration (MAX16127) 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: 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. P = ILOAD2 x RDS(ON) 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. 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 MOSFET Gate Protection 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. ���������������������������������������������������������������� Maxim Integrated Products 13 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Increasing the Operating Voltage Range resistors cannot 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. The MAX16126/MAX16127 can tolerate -30V to +90V. To increase the voltage 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 3). 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. 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 ISO7637-2 pulses. 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. It is important to compute the peak power dissipation in the series resistor. Most standard surface-mount DC-DC CONVERTER VBATT IN 10nF 10µF OUT GND 100I RS 100kI GATE SRC OUT IN D1 0.1µF 100kI SHDN D2 MAX16126 MAX16127 FLAG GND Figure 3. Circuit to Increase Operating Voltage Range ���������������������������������������������������������������� Maxim Integrated Products 14 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits VOUT VIN 10nF 100I GATE SRC COUT 10µF OUT IN 100kI SHDN 0.1µF TERM MAX16126 FLAG R1 UVSET R2 OVSET R3 GND Figure 4. MAX16126 Typical Operating Circuit ���������������������������������������������������������������� Maxim Integrated Products 15 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits VOUT VIN 10nF 10µF 100I GATE SRC OUT R3 IN 100kI SHDN 0.1µF OVSET MAX16127 TERM R4 R1 UVSET FLAG R2 GND Figure 5. MAX16127 Typical Operating Circuit ���������������������������������������������������������������� Maxim Integrated Products 16 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits GATE SRC CHARGE PUMP MAX16126 MAX16127 IN OUT UVLO POWER-OK TERM UVSET SHDN 1.225V FLAG CONTROL LOGIC OVSET THERMAL PROTECTION 1.225V GND Figure 6. MAX16126/MAX16127 Functional Diagram ���������������������������������������������������������������� Maxim Integrated Products 17 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Ordering Information PIN-PACKAGE TOP MARK MAX16126TCA+ PART 12 TQFN-EP* +ABV FUNCTION MAX16126TCB+ 12 TQFN-EP* +ABX MAX16126TCC+ 12 TQFN-EP* +ABY MAX16126TCD+ 12 TQFN-EP* +ABZ Latch mode MAX16127TC+ 12 TQFN-EP* +ABW Limiter mode Always autoretry Switch mode One retry, then latch Three retries, then latch Note: All devices are specified over the -40°C to +125°C temperature range. +Denotes a lead(Pb)-free/RoHS-compliant package. *EP = Exposed pad. Chip Information PROCESS: BiCMOS Package Information For the latest package outline information and land patterns (footprints), go to www.maxim-ic.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. 12 TQFN-EP T1233+4 21-0136 90-0019 ���������������������������������������������������������������� Maxim Integrated Products 18 MAX16126/MAX16127 Load-Dump/Reverse-Voltage Protection Circuits Revision History REVISION NUMBER REVISION DATE 0 11/11 DESCRIPTION Initial release PAGES CHANGED — 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. 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