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general description the max6495?ax6499 is a family of small, low-cur- rent, overvoltage-protection circuits for high-voltage transient systems such as those found in automotive and industrial applications. these devices monitor the input voltage and control an external n-channel mosfet switch to isolate the load at the output during an input overvoltage condition. the max6495?ax6499 operate over a wide supply voltage range from +5.5v to +72v. the gate of the n-channel mosfet is driven high while the monitored input is below the user-adjustable over- voltage threshold. an integrated charge-pump circuit provides a 10v gate-to-source voltage to fully enhance the n-channel mosfet. when the input voltage exceeds the user-adjusted overvoltage threshold, the gate of the mosfet is quickly pulled low, disconnect- ing the load from the input. in some applications, dis- connecting the output from the load is not desirable. in these cases, the protection circuit can be configured to act as a voltage limiter where the gate output saw- tooths to limit the voltage to the load (max6495/ max6496/max6499). the max6496 supports lower input voltages and reduces power loss by replacing the external reverse battery diode with an external series p-channel mosfet. the max6496 generates the proper bias voltage to ensure that the p-channel mosfet is on during normal operations. the gate-to-source voltage is clamped dur- ing load-dump conditions, and the p-channel mosfet is off during reverse-battery conditions. the max6497/MAX6498 feature an open-drain, undedi- cated comparator that notifies the system if the output falls below the programmed threshold. the max6497 keeps the mosfet switch latched off until either the input power or the shdn pin is cycled. the MAX6498 will autoretry when v ovset falls below 130mv. these devices are available in small, thermally enhanced, 6-pin and 8-pin tdfn packages and are fully specified from -40? to +125?. applications automotive industrial telecom/servers/networking firewire notebook computers features ? wide supply voltage range: +5.5v to +72v ? overvoltage-protection switch controller allows user to size external n-channel mosfets ? fast gate shutoff during overvoltage with 100ma sink capability ? internal charge-pump circuit ensures 10v gate-to-source enhancement for low r ds(on) performance ? n-channel mosfet latches off after an overvoltage condition (max6497/max6499) ? adjustable overvoltage threshold ? thermal shutdown protection ? supports series p-channel mosfet for reverse- battery voltage protection (max6496) ? pok indicator (max6497/MAX6498) ? adjustable undervoltage threshold (max6499) ? -40? to +125? operating temperature range ? small, 3mm x 3mm tdfn package max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet ________________________________________________________________ maxim integrated products 1 12 3 65 4 in shdn ovset outfb gate gnd max6495 3mm x 3mm tdfn top view pin configurations ordering information 19-3778; rev 0; 7/05 for pricing, delivery, and ordering information, please contact maxim/dallas direct! at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. ordering information continued at end of data sheet. + denotes lead-free package. firewire is a registered trademark of apple computer, inc. part temp range pin- package top mark max6495 att+t -40? to +125? 6 tdfn-6 ajm max6496 ata+t -40? to +125? 8 tdfn-8 aof pin configurations continued at end of data sheet. selector guide appears at end of data sheet.
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet 2 _______________________________________________________________________________________ absolute maximum ratings (all pins referenced to gnd.) electrical characteristics (v in = 14v, c gate = 6nf, t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) (note 1) stresses beyond those listed under ?bsolute maximum ratings?may cause permanent damage to the device. these are stress rating s only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specificatio ns is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. in, gate, gatep ...................................................-0.3v to +80v shdn , clear .............................................-0.3v to (v in + 0.3v) pok, outfb ..........................................................-0.3v to +80v gate to outfb .....................................................-0.3v to +12v gatep to in ...........................................................-12v to +0.3v ovset, uvset, pokset .......................................-0.3v to +12v current sink/source (all pins).............................................50ma all other pins to gnd ..................................-0.3v to (v in + 0.3v) continuous power dissipation (t a = +70?) 6-pin tdfn (derate 18.2mw/? above +70?) .........1455mw 8-pin tdfn (derate 18.2mw/? above +70?) .........1455mw operating temperature range .........................-40? to +125? junction temperature ......................................................+150? storage temperature range .............................-60? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units supply voltage range v in 5.5 72.0 v shdn = high 100 150 shdn = low (max6497/MAX6498/ max6499) 15 24 input supply current i in no load shdn = low (max6495/max6496) 24 32 ? in undervoltage lockout v in rising, enables gate 4.75 5 5.25 v in undervoltage lockout hysteresis v in falling, disables gate 155 mv v th+ ovset rising 1.22 1.24 1.26 ovset threshold voltage (max6495/max6496) v th- ovset falling 1.18 v ovset threshold hysteresis (max6495/max6496) v hyst ovset falling 5 % v th+ ovset rising 0.494 0.505 0.518 ovset threshold voltage (max6497/MAX6498) v th- ovset falling 0.13 v v th+ ovset rising 1.22 1.24 1.26 ovset threshold voltage (max6499) v th- ovset falling 1.18 v v th+ uvset rising 1.22 1.24 1.26 uvset threshold voltage (max6499) v th- uvset falling 1.18 v ovset/uvset threshold hysteresis (max6499) v hyst ovset falling 5 % v pokset+ pokset rising 1.22 1.24 1.26 pokset threshold voltage (max6497/MAX6498) v pokset- pokset falling 1.18 v pokset threshold hysteresis (max6497/ MAX6498) v hyst pokset falling 5 % ovset, uvset, pokset input current i set -50 +50 na startup response time t start shdn rising (note 2) 100 ? gate rise time gate rising from gnd to v outfb + 8v, outfb = gnd 1 ms
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet _______________________________________________________________________________________ 3 note 1: specifications to -40? are guaranteed by design and not production tested. note 2: the max6495?ax6499 power up with the external mosfet in off mode (v gate = gnd). the external mosfet turns on t start after all input conditions are valid. note 3: for accurate overtemperature-shutdown performance, place the device in close thermal contact with the external mosfet. electrical characteristics (continued) (v in = 14v, c gate = 6nf, t a = -40? to +125?, unless otherwise noted. typical values are at t a = +25?.) (note 1) parameter symbol conditions min typ max units ovset to gate propagation delay t ov set rising from v th - 100mv to v th + 100mv 0.6 ? uvset to gate, pokset to pok propagation delay pokset, uvset falling from v th + 100mv to v th - 100mv 20 ? v outfb = v in = 5.5v, r gate to in = 1m ? + + + = 14v, r gate to in = 1m ? v in + 8 v in + 10 v in + 11 v gate sinking 20ma, outfb = gnd 1 gate output low voltage v ol v in = 5.5v, gate sinking 1ma, outfb = gnd 0.9 v gate charge-pump current i gate gate = gnd 100 ? gate to outfb clamp voltage v clmp 12 18 v in to gatep output low voltage i gatep _ sink = 75?, i gatep _ source = 1? 7.5 11.7 v in to gatep clamp voltage v in = 24v, i gatep _ source = 10? 12 18 v shdn , clear logic-high input voltage v ih 1.4 shdn , clear logic-low input voltage v il 0.4 v shdn input pulse width 7s clear input pulse width 0.5 ? shdn , clear input pulldown current shdn is internally pulled down to gnd 0.6 1.0 1.4 ? thermal shutdown (note 3) +160 ? thermal-shutdown hysteresis 20 ? pokset to pok delay (max6497/MAX6498) 35 ? v in 14v, pokset = gnd, i sink = 3.2ma 0.4 pok output low voltage (max6497/MAX6498) v ol v in 2.8v, pokset = gnd, i sink = 100? 0.4 v pok leakage current (max6497/MAX6498) v pokset = 14v 100 na
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet 4 _______________________________________________________________________________________ t ypical operating characteristics (v in = +12v, t a = +25?, unless otherwise noted.) supply current vs. supply voltage max6495 toc01 supply voltage (v) supply current ( a) 65 55 45 35 25 15 35 60 85 110 135 10 575 set = gnd, gate enhanced supply current vs. temperature max6495 toc02 temperature ( c) supply current ( a) 110 95 -25 -10 5 35 50 65 20 80 102.5 105.0 107.5 110.0 112.5 115.0 117.5 120.0 100.0 -40 125 set = gnd, gate enhanced shutdown supply current vs. supply voltage max6495 toc03 supply voltage (v) shutdown supply current ( a) 65 55 45 35 25 15 20 30 40 50 10 575 set = gnd, shdn = gnd max6496 gate voltage vs. supply voltage max6495 toc04 supply voltage (v) v gate - v in (v) 65 55 45 35 25 15 3 6 9 12 0 575 set = gnd, in = outfb = shdn gatep voltage vs. supply voltage max6495 toc05 supply voltage (v) v in - v gatep (v) 65 55 45 35 25 15 3 6 9 12 0 575 set = gnd, in = outfb = shdn uvlo threshold vs. temperature max6495 toc06 temperature ( c) uvlo threshold (v) 110 95 65 80 -10 5 20 35 50 -25 4.6 4.7 4.8 4.9 5.0 5.1 5.2 5.3 5.4 5.5 4.5 -40 125 set = gnd, in = outfb = shdn falling rising set threshold vs. temperature max6495 toc07 temperature ( c) set threshold (v) 110 95 80 65 50 35 20 5 -10 -25 1.15 1.20 1.25 1.30 1.35 1.40 1.10 -40 125 in = shdn falling rising gate to outfb clamp voltage vs. temperature max6495 toc08 temperature ( c) v gate - v outfb (v) 110 95 65 80 -10 5 20 35 50 -25 15.6 15.7 15.8 15.9 16.0 16.1 16.2 16.3 16.4 16.5 15.5 -40 125 set = outfb = gnd in = shdn
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet _______________________________________________________________________________________ 5 startup waveform (c in = 100 f, c out = 10 f, r out = 100 ? ) max6495 toc09 400 s/div v in 10v/div v gate 10v/div v out 10v/div startup from shutdown (c in = 100 f, c out = 10 f, r out = 100 ? ) max6495 toc10 400 s/div v shdn 1v/div v gate 10v/div v out 10v/div overvoltage switch fault (c in = 100 f, c out = 10 f, r out = 100 ? ) max6495 toc11 200 s/div v in 20v/div v gate 20v/div v out 20v/div overvoltage limiter (c in = 100 f, c out = 10 f, r out = 100 ? ) max6495 toc12 400 s/div v in 20v/div v gate 20v/div v out 20v/div trip threshold = 28v t ypical operating characteristics (continued) (v in = +12v, t a = +25?, unless otherwise noted.)
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet 6 _______________________________________________________________________________________ pin description pin max6495 max6496 max6497/MAX6498 max6499 name function 1111 in positive supply voltage. connect in to the positive side of the input voltage. bypass in with a 10? capacitor to gnd. 2222 shdn shutdown input. drive shdn low to force gate low and turn off the external n-channel mosfet. drive shdn low and then high to reset the overvoltage-condition latch. shdn is internally pulled to gnd with 1? of current. connect shdn to in for normal operation. 3333 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 resistor network to the input side (drain) of the n-channel mosfet for overvoltage switch turn-off applications or to the output side (source) of the n-channel mosfet for overvoltage-limiting applications (max6495/max6496/max6499). 45 55 gnd ground 56 66 gate gate-driver output. connect gate to the gate of the external n-channel mosfet switch. gate is the output of a charge pump with a 100? pullup current to 10v (typ) above in during normal operation. gate is quickly clamped to outfb during an overvoltage condition. gate pulls low when shdn is low. 6777 outfb output-voltage-sense input. connect outfb to the source of the external n-channel mosfet switch. 4 gatep p-channel gate-driver output. connect gatep to the gate of an external p-channel mosfet to provide low-drop reverse-voltage protection. gatep is biased to ensure that the p-channel mosfet is on during normal operating modes, the gate-to-source is not overstressed during load-dump/overvoltage conditions, and the p-channel mosfet is off during reverse-battery conditions. 8 n.c. no connection. not internally connected. 4 pok power-ok output. pok is an open-drain output. pok remains low while pokset is below the internal pokset threshold. pok goes high impedance when pokset goes above the internal pokset threshold. connect pok to an external pullup resistor. 8 pokset power-ok threshold-adjustment input. pok remains low while pokset is below the internal pokset threshold (1.18v). pok goes high impedance when pokset goes above the internal pokset threshold (1.24v). connect a resistive divider from outfb to pokset to adjust the desired undervoltage threshold. 4 clear latch clear input. connect clear to a logic-high to latch the device off after an overvoltage condition. with ovset below v th , pulse clear low (5? typ) to reset the output latch. connect clear to gnd to make the latch transparent. 8 uvset undervoltage-threshold adjustment input. connect uvset to an external resistive voltage-divider network to adjust the desired undervoltage threshold. ep ep ep ep ep exposed pad. ep is internally connected to gnd. connect ep to the ground plane to provide a low thermal-resistance path from the ic junction to the pc board. do not use as the primary electrical connection to gnd.
detailed description overvoltage monitoring when operating in overvoltage mode, the max6495 max6499 feedback path (figure 1) consists of in, ovset? internal comparator, the internal gate charge pump, and the external n-channel mosfet, resulting in a switch-on/off function. when the programmed over- voltage threshold is tripped, the internal fast compara- tor turns off the external mosfet, clamping gate to outfb within 0.5? and disconnecting the power source from the load. when in decreases below the adjusted overvoltage threshold, the max6495?ax6499 slowly enhance gate above outfb, reconnecting the load to the power source. overvoltage limiter (max6495/max6496/max6499) when operating in overvoltage-limiter mode, the max6495/max6496/max6499 feedback path (figure 2) consists of outfb, ovset? internal comparator, the internal gate charge pump, and the external n-channel mosfet, resulting in the external mosfet operating as a voltage regulator. during normal operation, gate is enhanced 10v above outfb. the external mosfet source voltage is moni- tored through a resistive divider between outfb and ovset. when outfb rises above the adjusted over- voltage threshold, an internal comparator sinks the charge-pump current, discharging the external gate, regulating outfb at the ovset overvoltage threshold. outfb remains active during the overvoltage transients and the mosfet continues to conduct during the over- voltage event, operating in switched-linear mode. as the transient begins decreasing, outfb fall time will depend on the mosfet? gate charge, the internal charge-pump current, the output load, and the tank capacitor at outfb. for fast-rising transients and very large-sized mosfets, add an additional bypass capacitor from gate to gnd to reduce the effect of the fast-rising voltages at in. the external capacitor acts as a voltage-divider working against the mosfet? drain-to-gate capacitance. for a 6000pf gate-to-source capacitance, a 0.1? capacitor at gate will reduce the impact of the fast-rising v in input. caution must be exercised when operating the max6495/max6496/max6499 in voltage-limiting mode for long durations. if the v in is a dc voltage greater than the mosfet? maximum gate voltage, the mosfet dis- sipates power continuously. to prevent damage to the external mosfet, proper heatsinking should be imple- mented. gate voltage the max6495?ax6499 use a high-efficiency charge pump to generate the gate voltage. upon v in exceed- ing the 5v (typ) uvlo threshold, gate enhances 10v above v in (for v in 14v) with a 100? pullup current. an overvoltage condition occurs when the voltage at ovset goes above its v th+ threshold. when the threshold is crossed, gate falls to outfb within 0.5? with a 100ma pulldown current. the max6495?ax6499 include an internal clamp to outfb that ensures gate is limited to 18v (max) above outfb to prevent gate- to-source damage of the external mosfet. max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet _______________________________________________________________________________________ 7 ovset gnd gate in outfb r1 v in v out r2 max6495 max6499 figure 1. overvoltage threshold (max6495?ax6499) ovset gnd gate in outfb r1 c out v in v out r2 max6495 max6496 max6499 figure 2. overvoltage-limiter protection switch configuration
max6495?ax6499 the gate cycles during overvoltage-limit and overvolt- age-switch modes are quite similar but have distinct characteristics. in overvoltage-switch mode, gate is enhanced to (v in + 10v) while the monitored v in volt- age remains below the overvoltage fault threshold (ovset < v th+ ). when an overvoltage fault occurs (ovset v th+ ), gate is pulled one diode drop below outfb, turning off the external mosfet and discon- necting the load from the input. gate remains low (mosfet off) as long as the v in voltage is above the overvoltage fault threshold. as v in falls back below the overvoltage fault threshold, gate is again enhanced to (v in + 10v). in overvoltage-limit mode, gate is enhanced to (v in +10v) while the monitored outfb voltage remains below the overvoltage fault threshold (ovset < v th+ ). when an overvoltage fault occurs (ovset v th+ ), gate is pulled one diode drop below outfb until outfb drops 5% below the overvoltage fault threshold (max6495/max6496/max6499). gate is then turned back on until outfb reaches the overvoltage fault threshold and gate is again turned off. gate cycles in a sawtooth waveform until outfb remains below the overvoltage fault threshold and gate remains con- stantly on (v in +10v). the overvoltage limiter? saw- tooth gate output operates the mosfet in a switched-linear mode while the input voltage remains above the overvoltage fault threshold. the sawtooth fre- quency depends on the load capacitance, load current, and mosfet turn-on time (gate charge current and gate capacitance). gate goes high when the following startup conditions are met: v in is above the uvlo threshold, shdn is high, an overvoltage fault is not present, and the device is not in thermal shutdown. undervoltage monitoring (max6499) the max6499 includes undervoltage and overvoltage comparators for window detection (see figures 3 and 12). gate is enhanced and the n-channel mosfet is on when the monitored voltage is within the selected ?indow.?when the monitored voltage falls below the lower limit (v triplow ) or exceeds the upper limit (v triphigh ) of the window, gate falls to outfb turn- ing off the mosfet. the application in figure 3 shows the max6499 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: where r total = r1 + r2 + r3. 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. because the max6499 has very high input impedance, r total can be up to 5m ? . 2) calculate r3 based on r total and the desired upper trip point: 3) calculate r2 based on r total , r3, and the desired lower trip point: 4) calculate r1 based on r total , r2, and r3: r1 = r total ?r2 ?r3 r vr v r th total triplow 23 = () ? ? ? ? ? ? ? ? ? ? r vr v th total triphigh 3 = + vv r rr vv r r triplow th total triphigh th total = () + ? ? ? ? ? ? = () ? ? ? ? ? ? ? + 23 3 72v, overvoltage-protection switches/limiter controllers with an external mosfet 8 _______________________________________________________________________________________ ovset gnd clear gate outfb in shdn uvset r2 v in r3 r1 max6499 dc-dc converter gnd in out figure 3. max6499 window-detector circuit
power-ok output (max6497/MAX6498) pok is an open-drain output that remains low when the voltage at pokset is below the internal pokset threshold (1.18v). pok goes high impedance when pokset goes above the internal pokset threshold (1.24v). connect a resistive divider from outfb to pokset to adjust the desired undervoltage threshold. use a resistor in the 100k ? range from pokset to gnd to minimize current consumption. overvoltage latch function the max6497/max6499 offers a latch function that pre- vents the external mosfet from turning on until the latch is cleared. for the max6497, the latch can be cleared by cycling the power on the input in to a volt- age below the undervoltage lockout or by pulling the shutdown input low and then back to a logic-high state. the max6499 offers a clear input that latches the n-mosfet off when clear is high. the latch is removed when the clear input is plused low. connect clear low to make the latch transparent. overvoltage retry function the MAX6498 offers an automatic retry function that tries to enhance the external n-channel mosfet after the overvoltage condition is removed. when the monitored input voltage detects an overvoltage condition (v set > v th+ ), the n-mosfet is turned off. the mosfet stays off until the voltage at v set falls below its v th- (typically 0.13v), at which point the output tries to turn on again. applications information load dump most automotive applications run off a multicell ?2v lead-acid battery with a nominal voltage that swings between 9v and 16v (depending on load current, charging status, temperature, battery age, etc.). the battery voltage is distributed throughout the automobile and is locally regulated down to voltages required by the different system modules. load dump occurs when the alternator is charging the battery and the battery becomes disconnected. the alternator voltage regula- tor is temporarily driven out of control. power from the alternator flows into the distributed power system and elevates the voltage seen at each module. the voltage spikes have rise times typically greater than 5ms and decays within several hundred milliseconds but can extend out to 1s or more depending on the characteris- tics of the charging system. these transients are capa- ble of destroying sensitive electronic equipment on the first ?ault event. setting overvoltage thresholds ovset provides an accurate means to set the overvolt- age level for the max6495?ax6499. use a resistive divider to set the desired overvoltage condition (see figure 2). ovset has a rising 1.24v threshold with a 5% falling hysteresis (max6495/max6496/max6499) and a rising 0.505v threshold with a falling 0.15v threshold (max6497/MAX6498). begin by selecting the total end-to-end resistance, r total = r1 + r2. choose r total to yield a total cur- rent equivalent to a minimum 100 x i set (ovset? input bias current) at the desired overvoltage threshold. for example: with an overvoltage threshold (v ov ) set to 20v for the max6495/max6496/max6499, r total < 20v / (100 x i set ), where i set is ovset? 50na (max) input bias current. r total < 4m ? use the following formula to calculate r2: where v th+ is the 1.24v ovset rising threshold and v ov is the desired overvoltage threshold. r2 = 246k ? . use a 243k ? standard resistor. r total = r2 + r1, where r1 = 3.754m ? . use a 3.74m ? standard resistor. a lower value for total resistance dissipates more power but provides slightly better accuracy. reverse-battery protection the max6496 is an overvoltage-protection circuit that is capable of driving a p-channel mosfet to prevent reverse-battery conditions. this mosfet eliminates the need for external diodes, thus minimizing the input volt- age drop (see figure 7). inrush/slew-rate control inrush current control can be implemented by placing a capacitor from gate to gnd to slowly ramp up the gate, thus limiting the inrush current and controlling gate? slew rate during initial turn-on. the inrush cur- rent can be approximated using the following equation: where i gate is gate? 100? sourcing current, i load is the load current at startup, and c out is the output capacitor. i c c ii inrush out gate gate load =+ rv r v th total ov 2 = + max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet _______________________________________________________________________________________ 9
max6495?ax6499 mosfet selection select external mosfets according to the application current level. the mosfet? on-resistance (r ds(on) ) should be chosen low enough to have a minimum volt- age drop at full load to limit the mosfet power dissi- pation. determine the device power rating to accommodate an overvoltage fault when operating the max6495/max6496/max6499 in overvoltage-limit mode. during normal operation, the external mosfet dissi- pates little power. the power dissipated in the mosfet during normal operation is: p= i load 2 x r ds(on) where p is the power dissipated in the mosfet, i load is the output load current, and r ds(on) is the drain-to- source resistance of the mosfet. most power dissipation in the mosfet occurs during a prolonged overvoltage event when operating the max6495/max6496/max6499 in voltage-limiter mode. the power dissipated across the mosfet is as follows (see the thermal shutdown in overvoltage-limiter mode section): p = v ds x i load where v ds is the voltage across the mosfet? drain and source. thermal shutdown the max6495?ax6499 thermal-shutdown feature turns off gate if it exceeds the maximum allowable thermal dissipation. thermal shutdown also monitors the pc board temperature of the external n-channel mosfet when the devices sit on the same thermal island. good thermal contact between the max6495 max6499 and the external n-channel mosfet is essen- tial for the thermal-shutdown feature to operate effec- tively. place the n-channel mosfet as close to possible to outfb. when the junction temperature exceeds t j = +160?, the thermal sensor signals the shutdown logic, turning off the gate output and allowing the device to cool. the thermal sensor turns the gate on again after the ic? junction temperature cools by 20?. thermal-over- load protection is designed to protect the max6495 max6499 and the external mosfet in the event of cur- rent-limit fault conditions. for continuous operation, do not exceed the absolute maximum junction-tempera- ture rating of t j = +150?. thermal shutdown in overvoltage-limiter mode when operating the max6495/max6496/max6499 in overvoltage-limit mode for a prolonged period of time, a thermal shutdown is possible. the thermal shutdown is dependent on a number of different factors: ? the device? ambient temperature ? the output capacitor (c out ) ? the output load current (i out ) ? the overvoltage threshold limit (v ov ) ? the overvoltage waveform period (t ov ) ? the power dissipated across the package (p diss ) during an initial overvoltage occurrence, the discharge time ( ? t 1 ) of c out , caused by i out and i gatepd . the discharge time is approximately: where v ov is the overvoltage threshold, i out is the load current, and i gatepd is the gate? 100ma pull- down current. upon out falling below the threshold point, the max6495/max6496/max6499s?charge-pump current must recover and begins recharging the external gate voltage. the time needed to recharge gate from -v d to the mosfet? gate threshold voltage is: where c iss is the mosfet? input capacitance, v gs(th) is the mosfet? gate threshold voltage, v d is the internal clamp (from outfb to gate) diode? for- ward voltage and i gate is the charge-pump current (100? typ). ? tc vv i iss gs th d gate 2 () = + ? tc v ii out ov out gatepd 1 095 . ( ) = + 72v, overvoltage-protection switches/limiter controllers with an external mosfet 10 ______________________________________________________________________________________ ? t 2 ? t 1 gate outfb ? t ov ? t 3 figure 4. max6495/max6496/max6499 timing
during ? t 2 , c out loses charge through the output load. the voltage across c out ( ? v 2 ) decreases until the mosfet reaches its v gs(th) threshold and can be approximated using the following formula: once the mosfet v gs(th) is obtained, the slope of the output-voltage rise is determined by the mosfet q g charge through the internal charge pump with respect to the drain potential. the new rise time needed to reach a new overvoltage event can be calculated using the following formula: where q gd is the gate-to-drain charge. the total period of the overvoltage waveform can be summed up as follows: t ov = ? t 1 + ? t 2 + ? t 3 the max6495/max6496/max6499 dissipate the most power during an overvoltage event when i out = 0. the maximum power dissipation can be approximated using the following equation: the die-temperature increase is related to jc (8.3?/w and 8.5?/w for the max6495/max6496/max6499, respectively) of the package when mounted correctly with a strong thermal contact to the circuit board. the max6495/max6496/max6499 thermal shutdown is governed by the equation: t j = t a + p diss x jc < +170? pv i t t diss ov gatepd ov . = 0 975 1 ? ? ? ? t q v v i gd gs out gate 3 ? ? ? vi t c out out 2 2 = max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet ______________________________________________________________________________________ 11 ovset gnd gate in shdn outfb 12v in max6495 dc-dc converter gnd in out figure 5. overvoltage limiter (max6495) ovset gnd gate in shdn gatep outfb 12v max6496 dc-dc converter gnd in out figure 6. overvoltage limiter with low-voltage-drop reverse- protection circuit (max6496) t ypical application circuits
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet 12 ______________________________________________________________________________________ ovset gnd pok gate outfb pokset shdn in 12v max6497 MAX6498 dc-dc converter gnd en in out figure 7. overvoltage protection to a dc-dc converter (max6497/MAX6498) t ypical application circuits (continued) ovset gnd clear gate outfb in shdn uvset r2 12v r3 r1 max6499 dc-dc converter gnd in out figure 8. overvoltage and undervoltage window detector (max6499) max6495 5v in uvlo 1.24v ovset gate outfb gnd shdn 10v charge pump thermal protection figure 9. functional diagram (max6495) functional diagrams max6496 5v in uvlo 1.24v ovset gatep i gatep_source gate outfb gnd shdn 10v charge pump thermal protection 10v figure 10. functional diagram (max6496)
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet ______________________________________________________________________________________ 13 max6497 MAX6498 5v in uvlo 0.505v 1.24v ovset gate outfb gnd shdn 10v charge pump thermal protection pok pokset figure 11. functional diagram (max6497/MAX6498) functional diagrams (continued) max6499 5v in uvlo 1.24v ovset 1.24v uvset gate outfb gnd clear shdn 10v charge pump thermal protection figure 12. functional diagram (max6499) selector guide part function p-channel driver pok function undervoltage latch/ autoretry package code max6495 ov switch/limiter t633-1 max6496 ov switch/limiter yes t833-1 max6497 ov switch yes latch t833-1 MAX6498 ov switch yes autoretry t833-1 max6499 ov/uv switch/limiter yes latch t833-1
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet 14 ______________________________________________________________________________________ chip information process: bicmos 134 865 n.c. gate gnd max6496 2 7 outfb in ovset gatep shdn 3mm x 3mm tdfn top view 134 865 pokset gate gnd max6497 MAX6498 2 7 outfb in ovset pok shdn 3mm x 3mm tdfn 134 865 uvset gate gnd max6499 2 7 outfb in ovset clear shdn 3mm x 3mm tdfn pin configurations (continued) ordering information (continued) + denotes lead-free package. part temp range pin- package top mark max6497 ata+t -40? to +125? 8 tdfn-8 aoc MAX6498 ata+t -40? to +125? 8 tdfn-8 aod max6499 ata+t -40? to +125? 8 tdfn-8 aoe
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet ______________________________________________________________________________________ 15 pa c kag e information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .) 6, 8, &10l, dfn thin.eps l c l c pin 1 index area d e l e l a e e2 n g 1 2 21-0137 package outline, 6,8,10 & 14l, tdfn, exposed pad, 3x3x0.80 mm -drawing not to scale- k e [(n/2)-1] x e ref. pin 1 id 0.35x0.35 detail a b d2 a2 a1
max6495?ax6499 72v, overvoltage-protection switches/limiter controllers with an external mosfet maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a maxim product. no circu it patent licenses are implied. maxim reserves the right to change the circuitry and specifications without notice at any time. 16 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 2005 maxim integrated products printed usa is a registered trademark of maxim integrated products, inc. heaney package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline info rmation, go to www.maxim-ic.com/packages .) common dimensions symbol min. max. a 0.70 0.80 d 2.90 3.10 e 2.90 3.10 a1 0.00 0.05 l 0.20 0.40 pkg. code n d2 e2 e jedec spec b [(n/2)-1] x e package variations 0.25 min. k a2 0.20 ref. 2.300.10 1.500.10 6 t633-1 0.95 bsc mo229 / weea 1.90 ref 0.400.05 1.95 ref 0.300.05 0.65 bsc 2.300.10 8 t833-1 2.00 ref 0.250.05 0.50 bsc 2.300.10 10 t1033-1 2.40 ref 0.200.05 - - - - 0.40 bsc 1.700.10 2.300.10 14 t1433-1 1.500.10 1.500.10 mo229 / weec mo229 / weed-3 0.40 bsc - - - - 0.200.05 2.40 ref t1433-2 14 2.300.10 1.700.10 t633-2 6 1.500.10 2.300.10 0.95 bsc mo229 / weea 0.400.05 1.90 ref t833-2 8 1.500.10 2.300.10 0.65 bsc mo229 / weec 0.300.05 1.95 ref t833-3 8 1.500.10 2.300.10 0.65 bsc mo229 / weec 0.300.05 1.95 ref -drawing not to scale- g 2 2 21-0137 package outline, 6,8,10 & 14l, tdfn, exposed pad, 3x3x0.80 mm downbonds allowed no no no no yes no yes no

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