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MAX16126/max16127 load-dump/reverse-voltage protection circuits ????????????????????????????????????????????????????????????????? maxim integrated products 1 19-6053; rev 0; 11/11 general description the MAX16126/max16127 load-dump/reverse-voltage protection circuits protect power supplies from dam - aging input voltage conditions, including overvoltage, reverse-voltage, and high-voltage transient pulses. using a built-in charge pump, the devices control two exter - nal 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 automo - tive cold-crank conditions. these devices feature a flag output ( flag ) that asserts during fault conditions. for reverse-voltage protection, external back-to-back mosfets outperform the traditional reverse-battery diode, minimizing the voltage drop and power dissipa - tion during normal operation. the MAX16126/max16127 use external resistors to adjust the overvoltage and undervoltage comparator thresholds for maximum flexibility. the max16127 provides limiter-mode fault manage - ment for overvoltage and thermal shutdown conditions; whereas the MAX16126 provides switch-mode fault management for overvoltage and thermal shutdown con - ditions. 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 (-40 n c to +125 n c). applications automotive industrial avionics telecom/server/networking benefits and features s operates down to +3v, riding out cold-crank conditions s -30v to +90v wide input voltage protection range s minimal operating voltage drop reverse-voltage protection s fast gate shutoff during fault conditions with complete load isolation s adjustable undervoltage/overvoltage thresholds s thermal shutdown protection s low supply current and low shutdown current s charge-pump circuit enhances external n-channel mosfets s flag output identifies fault condition s automotive qualified s -40 n c to +125 n c operating temperature range s available 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 . for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxims website at www.maxim-ic.com.
????????????????????????????????????????????????????????????????? maxim integrated products 2 MAX16126/max16127 load-dump/reverse-voltage protection circuits (all pins referenced to gnd.) in ............................................................................ -30v to +90v shdn ............................................ -0.3v to max (0v, v in + 0.3v) term ............................................ -0.3v to max (0v, v in + 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) ................................. q 100ma continuous power dissipation (t a = +70 n c) (multilayer board) tqfn (derate 14.7mw/ n c above +70 n c) ............... 1176.5mw operating temperature range ........................ -40 n c to +125 n c junction temperature ..................................................... +150 n c storage temperature range ............................ -60 n c to +150 n c lead temperature (soldering, 10s) ................................ +300 n c soldering temperature (reflow) ...................................... +260 n c tqfn junction-to-ambient thermal resistance ( b ja ) .......... 68 n c/w junction-to-case thermal resistance ( b jc ) ............... 11 n c/w absolute maximum ratings 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.maxim-ic.com/thermal-tutorial . stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional opera - tion 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) electrical characteristics (v in = 12v, c gate-source = 1nf, t a = -40 n c to +125 n c, unless otherwise noted. typical values are at t a = +25 n c.) (note 2) parameter symbol conditions min typ max units input voltage range v in operating range 3 24 v protection range -30 +90 input supply current i in shdn = high 224 320 f a shdn = low 34 50 src input current i src 75 110 f a in undervoltage lockout v uvlo v in rising 2.8 v ovset/uvset input current i uvset/ovset 500 na ovset/uvset threshold (rising) v th v in rising 1.2 1.225 1.25 v ovset/uvset threshold hysteresis v th-hys 5 % pok threshold rising v pok+ 0.9 x v in v pok threshold falling v pok- 0.87 x v in v term on-resistance r term 0.7 1.2 k i startup response time t start (note 3) 150 f s autoretry timeout t retry 150 ms gate rise time t rise v gate rising (gnd to v src + 6v) 1 ms ovset to gate propagation delay t ovg v ovset rising (v th - 100mv to v th + 100mv) 0.55 f s uvset to gate propagation delay t uvg v uvset rising (v th - 100mv to v th +100mv) 20 f s
????????????????????????????????????????????????????????????????? maxim integrated products 3 MAX16126/max16127 load-dump/reverse-voltage protection circuits note 2: all parameters are production tested at t a = +25 n c. limits over the operating temperature range are guaranteed by design. note 3: the MAX16126/max16127 power up with the external mosfets in off mode (v gate = v src ). the external mosfets turn on t start after the ic is powered up and all input conditions are valid. electrical characteristics (continued) (v in = 12v, c gate-source = 1nf, t a = -40 n c to +125 n c, unless otherwise noted. typical values are at t a = +25 n c.) (note 2) parameter symbol conditions min typ max units ovset to flag propagation delay t ov v ovset rising (v th - 100mv to v th + 100mv) 0.3 f s gate output voltage high above v src v ohgate v in = v src = v out = 3v, i gate = -1 f a 4.3 4.7 6 v v in = v src = v out = 12v, i gate = -1 f a 6.25 7 8 gate pulldown current i pd v gate = 12v 8.8 ma gate charge-pump current i gat e v in = v gate = v src = 12v 155 f a thermal shutdown t + +145 n c thermal shutdown hysteresis t 15 n c shdn logic-high input voltage v ih 1.4 v shdn logic-low input voltage v il 0.4 v shdn input pulse width t pw 6 f s shdn input pulldown current i spd 0.8 1.2 f a flag output voltage low v ol flag sinking 1ma 0.4 v flag leakage current i il v flag = 12v 0.5 f a
????????????????????????????????????????????????????????????????? maxim integrated products 4 MAX16126/max16127 load-dump/reverse-voltage protection circuits typical operating characteristics (v in = 12 v, t a = +25 n c, unless otherwise noted.) supply current vs. supply voltage MAX16126 toc01 supply voltage (v) supply current (a) 30 20 10 100 150 200 250 300 50 04 0 shdn = high gate enhanced supply current vs. temperature MAX16126 toc02 temperature (c) supply current (a) 120 100 -20 0 20 60 40 80 170 190 210 230 250 270 290 310 150 -40 shdn = high gate enhanced shutdown supply current vs. supply voltage MAX16126 toc03 supply voltage (v) supply current (a) 24 18 12 6 20 30 40 50 60 70 80 90 100 10 03 0 shdn = low shutdown supply current vs. temperature MAX16126 toc04 temperature (c) supply current (a) 110 95 -25 -10 5 35 50 65 20 80 15 20 25 30 35 40 45 50 10 -40 125 shdn = low shdn pulldown current vs. temperature MAX16126 toc05 temperature (c) shdn pulldown current (a) 110 95 65 80 -10 5 20 35 50 -25 0.1 0.2 0.3 0.4 0.5 0.6 0.7 0.8 0.9 1.0 0 -40 125 gate to source voltage vs. supply voltage MAX16126 toc06 supply voltage (v) (v gate - v src ) (v) 21 18 6 9 12 15 3 4 5 6 7 8 9 10 2 32 4 gate-to-source voltage vs. temperature MAX16126 toc07 temperature (c) (v gate - v src ) (v) 110 95 -25 -10 5 35 50 65 20 80 4.5 5.0 5.5 6.0 6.5 7.0 7.5 8.0 4.0 -40 125 gate enhanced v in = v src = v out gate pulldown current vs. temperature MAX16126 toc08 temperature (c) gate pulldown current (ma) 8 11 14 17 20 5 110 95 -25 -10 53 55 06 5 20 80 -40 125 v gate = 12v v src = gnd gate pullup current vs. supply voltage MAX16126 toc09 supply voltage (v) gate pullup current (a) 25 20 5 10 15 135 140 145 150 155 160 165 170 130 03 0 v in = v gate = v src gate enhanced
????????????????????????????????????????????????????????????????? maxim integrated products 5 MAX16126/max16127 load-dump/reverse-voltage protection circuits typical operating characteristics (continued) (v in = 12v, t a = +25 n c, unless otherwise noted.) ovset threshold vs. temperature MAX16126 toc10a temperature (c) ovset threshold (v) 0.7 0.9 1.1 1.3 1.5 0.5 110 95 -25 -10 53 55 06 5 20 80 -40 125 falling rising uvset threshold vs. temperature MAX16126 toc10b temperature (c) uvset threshold (v) 0.7 0.9 1.1 1.3 1.5 0.5 110 95 -25 -10 53 55 06 5 20 80 -40 125 falling rising flag output low voltage vs. current MAX16126 toc11 flag current (ma) flag voltage (v) 1.5 1.0 0.5 0.1 0.2 0.3 0.4 0.5 0 02 .0 overvoltage fault to gate propagation delay vs. temperature MAX16126 toc12 temperature (c) propagation delay (s) 0.25 0.50 0.75 1.00 0 110 95 -25 -10 53 55 06 5 20 80 -40 125 v ovset pulsed from (v th - 100mv) to (v th + 100mv) reverse current vs. reverse voltage MAX16126 toc13 reverse voltage (v) reverse current (a) 25 20 15 10 5 5 10 15 20 25 30 0 03 0
????????????????????????????????????????????????????????????????? maxim integrated products 6 MAX16126/max16127 load-dump/reverse-voltage protection circuits typical operating characteristics (continued) (v in = 12v, t a = +25 n c, unless otherwise noted.) startup waveform (v in = 0 to 12v, r l = 100i , c in = 0.1f, c out = 100f) MAX16126 toc14 v in 10v/div v gate 10v/div v out 10v/div 400s/div startup from shutdown (shdn rising 0 to 2v, v in = 12v, r load = 100i , c in = 0.1f) MAX16126 toc15 v shdn 2v/div v gate 10v/div v out 10v/div 400s/div overvoltage switch fault (v ov = 20v, c in = 0.1f, c out = 100f) MAX16126 toc16 v in 20v/div v gate 10v/div v out 20v/div 100ms/div overvoltage limiter (v uv = 4v, v ov = 20v, c in = 0.1f, c out = 100f) MAX16126 toc17 v in 20v/div v gate 20v/div v out 10v/div 20ms/div
????????????????????????????????????????????????????????????????? maxim integrated products 7 MAX16126/max16127 load-dump/reverse-voltage protection circuits pin configuration 12 11 10 4 5 term n.c. 6 i.c. out 12 gate 3 98 7 in gnd ovset uvset ep src tqfn MAX16126 max16127 top view + flag shdn
????????????????????????????????????????????????????????????????? maxim integrated products 8 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 100k i 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. no connection. not internally connected. 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 ground 7 i.c. internally connected. connect to gnd. 8 flag flag output. during startup, flag is low as long as v out is lower than 90% of v in and after that it is high impedance. it asserts low during shutdown mode, an overvoltage, thermal shutdown, or undervoltage fault or when v out falls below 90% of v in . 9 out output voltage-sense input. connect out to the load with a 100 i series resistor. bypass with a minimum 10 f f 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 0.1 f f ceramic capacitor to gnd. ep exposed pad. can be connected to gnd or left unconnected.
????????????????????????????????????????????????????????????????? maxim integrated products 9 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 load- dump 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 cur - rent 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 manage - ment for overvoltage and thermal shutdown conditions, whereas the MAX16126 provides switch-mode fault management for overvoltage and thermal shutdown con - ditions. 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 gener - ate 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 150 f s 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 condi - tions 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 regu - lated 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 resis - tive 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 overvolt - age 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 overvolt - age 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 10 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 (v in < v th - v th-hys ), gate goes low, turning off the external mosfets and flag asserts. when the input voltage exceeds the undervolt - age threshold (v in > v th ), gate goes high after a 150 f s 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 tempera - ture exceeds +145 n c (t j ). 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 t j = +145 n c (typ), the internal thermal sensor signals the shutdown logic, pulling the gate voltage low and allowing the device to cool. when t j drops by 15 n c (typ), gate goes high and the mosfets turn back on. do not exceed the absolute maximum junction-temperature rating of t j = +150 n c. flag output ( flag ) an open-drain flag output indicates fault conditions. during startup, flag is initially low and goes high impedance when v out is greater than 90% of v in if no fault conditions are present. flag asserts low during shutdown mode, an overvoltage, thermal shutdown, or undervoltage fault, or when v out falls below 90% of v in . term connection the term connection has an internal switch to in. in shutdown ( shdn = gnd), this switch is open. by con - necting 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 cur - rent reduced. reverse-voltage protection the MAX16126/max16127 integrate reverse-voltage protection, preventing damage to the downstream cir - cuitry 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 0.1f ceramic capacitor from in to gnd, connect a 10nf ceramic capacitor from gate to src, connect 10f from output to gnd, and minimize the parasitic capaci - tance 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 protec - tion 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 regula - tion 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 - 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 val - ues 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 volt - age 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 11 MAX16126/max16127 load-dump/reverse-voltage protection circuits table 1. summary of iso7637 pulses 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 over - voltage 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 (v triplow ) or exceeds the upper limit (v triphigh ) 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: total triplow th th-hys r v (v - v ) r2 r3 ?? = ?? + ?? total triphigh th r vv r3 ?? = ?? ?? where r total = r1 + r2 + r3, v th is the 1.225v ovset/ uvset threshold, v th-hys is the hysteresis. use the following steps to determine the values for r1, r2, and r3: 1) choose a value for r total , the sum of r1, r2, and r3. 2) calculate r3 based on r total and the desired upper trip point: th total triphigh vr r3 v = 3) calculate r2 based on r total , r3, and the desired lower trip point: th th-hys total triplow (v - v ) r r2 - r3 v = 4) calculate r1 based on r total , r2, and r3: total r1 r - r2 - r3 = * relative to system voltage. name description peak voltage (v) (max) * duration 12v system pulse 1 inductive load disconnection -100 1ms to 2ms pulse 2a inductive wiring disconnection 50 0.05ms pulse 3a switching transients -150 0.2 f s pulse 3b 100 pulse 4 cold crank -7 100ms (initial) -6 up to 20s pulse 5a load dump (unsuppressed) 87 400ms (single) pulse 5b load dump (suppressed) (varies, but less than pulse 5a)
???????????????????????????????????????????????????????????????? maxim integrated products 12 MAX16126/max16127 load-dump/reverse-voltage protection circuits setting overvoltage and undervoltage thresholds (max16127) the max16127 operates in limiter mode and uses sepa - rate resistive dividers to set the undervoltage and over - voltage 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: total_ov th ov r r4 v v = where r total_uv = r3 + r4, v th is the 1.225v ovset rising threshold and v ov is the desired overvoltage threshold. the falling threshold of v th is 5% below the rising threshold. similarly, to calculate the values of r1 and r2: total_uv th th-hys uv r r2 (v - v ) v = where r total_uv = r1 + r2, v th is the 1.225v uvset rising threshold, v th-hys is the hysteresis, and v uv is the desired undervoltage threshold. use the nearest standard-value resistor that is less than the calculated value. a lower value for total resis - tance dissipates more power, but provides slightly better accuracy. mosfet selection mosfet selection is critical to design a proper protec - tion circuit. several factors must be taken into account: the gate capacitance, the drain-to-source voltage rating, the on-resistance (r ds(on) ), the peak power dissipation capability, and the average power dissipation limit. in general, both mosfets should have the same part num - ber. 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. figure 1. overvoltage and undervoltage window detector circuit (MAX16126) gnd gate v in 100ki 10nf src out in out dc-dc converter shdn term in uvset ovset gnd r1 r2 r3 MAX16126 0.1f flag 10f 100i
???????????????????????????????????????????????????????????????? maxim integrated products 13 MAX16126/max16127 load-dump/reverse-voltage protection circuits mosfet power dissipation the r ds(on) must be low enough to limit the mosfet power dissipation during normal operation. power dis - sipation (per mosfet) during normal operation can be calculated using this formula: p = i load 2 x r ds(on) where p is the power dissipated in each mosfet and i load is the average load current. during a fault condition in switch mode, the mosfets turn off and do not dissipate power. limiter mode impos - es the worst-case power dissipation. the average power can be computed using the following formula: p = i load x (v in - v out ) where p is the average power dissipated in both mosfets, i load is the average load current, v in is the input voltage, and v out is the average limited voltage on the output. in limiter mode, the output voltage is a sawtooth wave with characteristics determined by the r ds(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 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 v gs maximum rating. figure 2. overvoltage and undervoltage limiter protection configuration (max16127) gnd gate v in 100ki src in out dc-dc converter 100i shdn in out term ovset uvset gnd r3 r4 r1 r2 max16127 10nf 0.1f flag 10f
???????????????????????????????????????????????????????????????? maxim integrated products 14 MAX16126/max16127 load-dump/reverse-voltage protection circuits increasing the operating voltage range 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 cur - rent drawn by the zener diodes (see figure 3 ). 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 clamp - ing the low-energy iso7637-2 pulses. it is important to compute the peak power dissipation in the series resistor. most standard surface-mount 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 automotive- rated resistors. the shutdown input needs a series resistor to limit the current if v in exceeds the clamped voltage on in. a good starting point is 100k i . output reservoir capacitor the output capacitor can be used as a reservoir capaci - tor 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. figure 3. circuit to increase operating voltage range gnd gate v batt src out in out dc-dc converter shdn in gnd d1 d2 r s 100ki MAX16126 max16127 100ki 0.1f flag 100i 10f 10nf
???????????????????????????????????????????????????????????????? maxim integrated products 15 MAX16126/max16127 load-dump/reverse-voltage protection circuits figure 4. MAX16126 typical operating circuit gate v in r1 r2 r3 100ki src out v out c out 10f shdn term in uvset ovset gnd MAX16126 flag 100i 0.1f 10nf
???????????????????????????????????????????????????????????????? maxim integrated products 16 MAX16126/max16127 load-dump/reverse-voltage protection circuits figure 5. max16127 typical operating circuit gate v in 100ki src out v out shdn ovset r1 r3 r4 r2 term in uvset gnd max16127 flag 100i 0.1f 10nf 10f
???????????????????????????????????????????????????????????????? maxim integrated products 17 MAX16126/max16127 load-dump/reverse-voltage protection circuits figure 6. MAX16126/max16127 functional diagram 1.225v shdn power-ok charge pump out src gate control logi c uvlo 1.225v flag uvset ovset term in thermal protection gnd MAX16126 max16127
???????????????????????????????????????????????????????????????? maxim integrated products 18 MAX16126/max16127 load-dump/reverse-voltage protection circuits 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. chip information process: bicmos ordering information + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad. note: all devices are specified over the -40c to +125c temperature range. part pin-package top mark function MAX16126 tca+ 12 tqfn-ep* +abv switch mode always autoretry MAX16126tcb+ 12 tqfn-ep* +abx one retry, then latch MAX16126tcc+ 12 tqfn-ep* +aby three retries, then latch MAX16126tcd+ 12 tqfn-ep* +abz latch mode max16127 tc+ 12 tqfn-ep* +abw limiter mode package type package code outline no. land pattern no. 12 tqfn-ep t1233+4 21-0136 90-0019
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 products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 19 ? 2011 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. MAX16126/max16127 load-dump/reverse-voltage protection circuits revision history revision number revision date description pages changed 0 11/11 initial release

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