general description the max4785?ax4788 family of switches feature inter- nal current limiting to prevent host devices from being damaged due to faulty load conditions. these analog switches have a low 0.7 ? on-resistance and operate from a 2.3v to 5.5v input voltage range. they are avail- able with guaranteed 50ma and 100ma current limits, making them ideal for load-switching applications. when the switch is on and a load is connected to the port, a guaranteed blanking time of 14ms ensures that the transient voltages settle down. if after this blanking time the load current is greater than the current limit, the max4785 and max4787 enter a latch-off state where the switch is turned off and flag is issued to the microprocessor. the switch can be turned on again bycycling the power or the on pin. the max4786 and max4788 have an autoretry feature where the switch turns off after the blanking time and then continuously checks to see if the overload condi- tion is present. the switch remains on after the overload condition disappears. the max4785 and max4787 are available in a tiny space-saving 4-pin or 5-pin sc70 package. the max4786 and max4788 are available only in the 4-pin sc70 package. for higher current current-limiting switches, refer to the max4789?ax4794 and max1693 data sheets. applications pdas and palmtop devicescell phones gps systems hand-held devices features ? guaranteed current limit: 50ma, 100ma ? thermal-shutdown protection ? reverse-current protection ? 0.7 ? on-resistance ? 14ms guaranteed blanking time ? flag function (max4785/max4787) ? 65? supply current ? 8? latch-off current (max4785/max4787) ? 0.01? shutdown current ? 2.3v to 5.5v supply range ? undervoltage lockout ? fast current-limit response time ? tiny sc70 package max4785?ax4788 50ma/100ma current-limit switches ________________________________________________________________ maxim integrated products 1 ordering information 2.3v to 5.5v in out flag gnd on p to external port max4785max4787 t ypical operating circuit 19-2664; rev 1; 4/03 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. selector guide appears at end of data sheet. part temp range pin- package top mark max4785 exs-t -40? to +85? 4 sc70-4 age max4785exk-t -40? to +85? 5 sc70-5 adl max4786 exs-t -40? to +85? 4 sc70-4 agf max4787 exs-t -40? to +85? 4 sc70-4 agg max4787exk-t -40? to +85? 5 sc70-5 and max4788 exs-t -40? to +85? 4 sc70-4 agh gnd on 15 in out max4785max4787 sc70 top view 234 flag on 14 in out max4785 max4788 sc70 23 gnd pin configurations downloaded from: http:///
max4785?ax4788 50ma/100ma current-limit switches 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics(v in = 2.3v to 5.5v, t a = -40? to +85?, unless otherwise noted. typical values are at v in = 3.3v, t a = +25?.) (note 1) stresses beyond those listed under ?bsolute 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. in, on, flag , out to gnd .....................................-0.3v to +6v out short circuit to gnd .................................internally limited continuous power dissipation (t a = +70?) 4-pin sc70 (derate 3.1mw/? above +70?) ..............245mw 5-pin sc70 (derate 3.1mw/? above +70?) ..............247mw operating temperature range ...........................-40? to +85? junction temperature ......................................................+150? storage temperature range .............................-65? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units operating voltage v in 2.3 5.5 v v in = 2.3v to 5.0v 65 100 quiescent current i q v on = v in , i out = 0, switch on v in = 5.0v to 5.5v 120 ? latch-off current (note 2) i latch v on = v in , after an overcurrent fault (max4785/max4787) 81 5 a shutdown current i shdn v on = 0v 0.01 1 a max4785/max4786 50 120 forward current limit i fwd max4787/max4788 100 240 ma max4785/max4786 120 reverse current limit i rev max4787/max4788 240 ma on input leakage v on = v in or gnd -1 +1 ? off switch leakage v on = 0v, v out = 0v 0.01 1 a undervoltage lockout uvlo rising edge 1.8 2.2 v undervoltage lockout hysteresis 100 mv t a = +25?, i out = 20ma 0.7 1 on-resistance r on t a = -40? to +85?, i out = 20ma 1.3 ? on input logic high voltage v ih 2.0 v on input logic low voltage v il 0.8 v flag output logic low voltage i sink = 1ma (max4785/max4787) 0.4 v flag output high leakage current v in = v f lag = 5.5v (max4785/max4787) 1 a thermal shutdown 150 ? thermal-shutdown hysteresis 15 ? dynamic turn-on time (note 3) on from low to high; i out = 10ma, c l = 0.1? 50 ? turn-off time (note 3) on from high to low; i out = 10ma, c l = 0.1? 30 ns downloaded from: http:///
max4785?ax4788 50ma/100ma current-limit switches _______________________________________________________________________________________ 3 quiescent supply current vs. supply voltage max4785-01 supply voltage (v) supply current ( a) 5.5 5.0 4.0 4.5 3.0 3.5 2.5 10 20 30 40 50 60 70 80 90 0 2.0 6.0 v on = v in supply current vs. temperature max4785-02 temperature ( c) supply current ( a) 60 35 10 -15 10 20 30 40 50 60 70 80 90 0 -40 85 v on = v in v in = 5v v in = 3.3v latch-off current vs. temperature max4785 toc03 temperature ( c) latch-off ( a) 60 35 10 -15 1 2 3 4 5 6 7 8 9 10 11 12 13 1514 0 -40 85 v on = v in v in = 5v v in = 3.3v 10 0.001 -40 85 shutdown supply current vs. temperature 0.01 0.1 1 max4785-04 temperature ( c) shutdown supply current (na) 60 35 10 -15 10 -40 85 1 0.1 0.01 0.001 0.0001 shutdown leakage current vs. temperature max4785-05 temperature ( c) shutdown leakage current (na) 60 35 10 -15 v in = 5v v in = 3.3v latch-off leakage current vs. temperature max4785 toc06 temperature ( c) latch-off leakage current (na) 60 35 10 -15 0.001 0.01 0.1 1 10 100 0.0001 -40 85 v in = 5v v in = 3.3v t ypical operating characteristics (v in = 3.3v, t a = +25?, unless otherwise noted.) note 1: all parts are 100% tested at +25?. limits across the full temperature range are guaranteed by design and correlation. note 2: latch-off current does not include the current flowing into flag . note 3: the on-time is defined as the time taken for the current through the switch to go from 0ma to full load. the off-time is define d as the time taken for the current through the switch to go from full load to 0ma. note 4: retry time is typically 7x the blanking time. electrical characteristics (continued)(v in = 2.3v to 5.5v, t a = -40? to +85?, unless otherwise noted. typical values are at v in = 3.3v, t a = +25?.) (note 1) parameter symbol conditions min typ max units blanking time t blank overcurrent fault, figures 2, 3 14 60 ms short-circuit current-limitresponse time v on = v in = 3.3v, short circuit applied to out 5 s retry time (note 4) t retry max4786/max4788: overcurrent fault,figure 2 98 420 ms downloaded from: http:///
max4785?ax4788 50ma/100ma current-limit switches 4 _______________________________________________________________________________________ normalized on-resistance vs. temperature max4785-07 temperature ( c) normalized r on 60 35 10 -15 0.2 0.4 0.6 0.8 1.0 1.2 1.4 0 -40 85 v cc = 3.3v output current vs. output voltage max4785 toc08 v in - v out (v) output current (ma) 3.0 2.7 2.4 2.1 1.8 1.5 1.2 0.9 0.6 0.3 50 100 150 200 250 300 0 0 3.3 max4787/max4788 max4785/max4786 switch turn-on/off times vs. temperature max4785 toc09 temperature ( c) turn-on/off times ( s) 60 35 10 -15 0.01 0.1 1 10 100 0.001 -40 85 v cc = 3.3v i load = 10ma on off v cc = 5v flag-blanking timeout vs. temperature max4785 toc10 temperature ( c) flag-blanking time (ms) 60 35 10 -15 25 30 35 40 45 5020 -40 85 current-limit response max4785 toc11 40 s/div v on 2v/divi out 100ma/div v in 2v/div c out = 1 f v in = 3.3v c in = 1 f current-limit response max4785 toc12 20 s/div i out 100ma/div v in = v on 1v/div c out = 1 f v in = v on c in = 1 f t ypical operating characteristics (continued) (v in = 3.3v, t a = +25?, unless otherwise noted.) downloaded from: http:///
max4785?ax4788 50ma/100ma current-limit switches _______________________________________________________________________________________ 5 pin description switch turn-on time response max4785 toc14 100 s/div i out 10ma/div v on v in = 3.3v current-limit response (out shorted to gnd) max4785 toc13 40 s/div v out 2v/divi out 2a/div v in 2v/div c in = 1 f c out = 1 f t ypical operating characteristics (continued) (v in = 3.3v, t a = +25?, unless otherwise noted.) pin sc70 sc70 name function 11 out switch output. bypass with a 0.1? capacitor to ground. 22 gnd ground ? flag fault output. this open-drain output goes low when the device stays in forward or reversecurrent limit for more than the blanking time period. flag is high impedance when a fault is not present or when on is low. 34 on active-high switch-on input. a logic high turns the switch on. 45 in input. bypass with a 0.1? ceramic capacitor to ground. flag-blanking response max4785 toc16 4ms/div flag2v/div i out 100ma/div v in 2v/divv on 2v/div switch turn-off time response max4785 toc15 100ns/div v on 2v/divi out 10ma/div v in = 3.3v downloaded from: http:///
max4785?ax4788 detailed description the max4785?ax4788 are forward/reverse current-limited switches that operate from a 2.3v to 5.5v input voltage range and guarantee a 50ma and 100ma mini- mum current-limit threshold for different options. the voltage drop across an internal sense resistor is com- pared to two reference voltages to indicate a forward or reverse current-limit fault. when the load current exceeds the preset current limit for greater than the fault-blanking time, the switch opens. the max4786 and max4788 have an autoretry function that turns on the switch again after an internal retry time expires. if the faulty load condition is still present after the blanking time, the switch turns off again and the cycle is repeated. if the faulty load condition is not pre- sent, the switch remains on. the max4785 and max4787 do not have the autoretry option and the switch remains in latch-off mode until the on pin or the input power is cycled from high to low and then high again. the undervoltage lockout (uvlo) circuit prevents erro- neous switch operation when the input voltage goes too low during startup conditions. reverse-current protection the max4785?ax4788 limit the reverse current (v out to v in ) from exceeding the maximum i rev value. the switch is shut off and flag is asserted (max4785/ max4787) if the reverse current-limit condition persistsfor more than the blanking time. this feature prevents excessive reverse currents from flowing through the device. switch-on/off control toggle on high to enable the current-limited switches.the switches are continuously on, only if v in exceeds the uvlo threshold (typically 2v) and there is no fault.when a forward/reverse current fault is preset or the die exceeds the thermal-shutdown temperature of +150?, out is internally disconnected from in and the supply current decreases to 8 a (latch off). the switch is now operating in one of its off states. the switch off-state also occurs when driving on low, thus reducing the supply current (shutdown) to 0.01?. table 1 illustrates the on/off state of the max4785?ax4788 current- limit switches. 50ma/100ma current-limit switches 6 _______________________________________________________________________________________ n blanking time circuitry reverse-current detector forward current detector n +2.0v flagout in on gnd max4785/max4787 only logic auto- retry max4785?ax4788 undervoltage lockout figure 1. max4785?ax4788 functional diagram downloaded from: http:///
flag indicator the max4785 and max4787 feature a latched fault out-put, flag . whenever a fault is activated, it latches flag output low and also turns the switch off. flag is an open-drain output transistor and requires an exter- nal pullup resistor from flag to in. during shutdown (on is low), the pulldown on flag output is released in order to limit power dissipation. flag goes low when any of the following conditions occur: the die temperature exceeds the thermal-shutdowntemperature limit of +150?. the device is in current limit for more than the fault-blanking period. ? in is below uvlo threshold. autoretry (max4786/max4788) when the forward or reverse current-limit threshold isexceeded, t blank timer begins counting (figure 2). the timer resets if the overcurrent condition disappearsbefore t blank has elapsed. a retry time delay, t retry , is started immediately after t blank has elapsed and during that time, the switch is latched off. at the end oft retry , the switch is turned on again. if the fault still exists, the cycle is repeated. if the fault has beenremoved, the switch stays on. the autoretry feature saves system power in the case of an overcurrent or short-circuit condition. during t blank , when the switch is on, the supply current is at the current limit. during t retry , when the switch is off, the current through the switch is zero. instead ofobserving the full load current, the switch sees the equivalent load current times duty cycle or i supply = i load ? t blank /(t blank + t retry ). with a typical t blank = 37ms and typical t retry = 259ms, the duty cycle is 12%, which results in an 88% power savingsover the switch being on the entire time. the duty cycle is consistent across the process and devices. latch off (max4785/max4787) when the forward or reverse current-limit threshold isexceeded, t blank timer begins counting. the timer resets if the overcurrent condition disappears beforet blank has elapsed. the switch is shut off if the over- current condition continues up to the end of the blank-ing time. reset the switch by either toggling on (figure 3a) or cycling the input voltage below uvlo, typically 2v (figure 3b). fault blanking the max4785?ax4788 feature 14ms (min) faultblanking. fault blanking allows current-limit faults, including momentary short-circuit faults that occur when hot swapping a capacitive load, and also ensures that no fault is issued during power-up. when a load transient causes the device to enter current limit, an internal counter starts. if the load-transient fault persists beyond the fault-blanking timeout, the max4785 and max4787s? flag asserts low. load-transient faults less than t blank do not cause a flag output assertion. only current-limit faults are blanked. a thermal fault and input voltage drops below the uvlo threshold cause flag to assert immediately and do not wait for the blanking time. thermal shutdown the max4785?ax4788 have a thermal shutdown fea- ture to protect the devices from overheating. the switch turns off and flag goes low immediately (no fault blank- ing) when the junction temperature exceeds +150?. max4785?ax4788 50ma/100ma current-limit switches _______________________________________________________________________________________ 7 on fault switch on/off supply current mode low x off shutdown high undervoltage lockout off shutdown high thermal off immediately (t blank period does not apply) latch off off after t blank period has elapsed latch off high current limit on during t blank period, off during t retry period for the max4786 and max4788; cycle repeats until fault is removed see the autoretry section table 1. max4785?ax4788 switch truth table load current switch status t blank off on t retry current limit short condition removed t blank t blank figure 2. max4786/max4788 autoretry fault blanking diagram downloaded from: http:///
max4785?ax4788 the switches with autoretry feature turn back on whenthe device temperature drops approximately 15?. the switches with latchoff feature require on cycling. applications information input capacitor to limit the input voltage drop during momentary outputshort-circuit conditions, connect a capacitor from in to gnd. a 0.1? ceramic capacitor is adequate for most applications; however, higher capacitor values further reduce the voltage drop at the input and are recom- mended for lower voltage applications. output capacitance connect a 0.1? capacitor from out to gnd. thiscapacitor helps prevent inductive parasitics from pulling out negative during turn-off, thus preventing the max4785?ax4788 from tripping erroneously. ifthe load capacitance is too large, then current may not have enough time to charge the capacitance and the device assumes that there is a faulty load condition. the maximum capacitive load value that can be driven from out is obtained by the following formula: layout and thermal dissipation to optimize the switch response time to output short-circuit conditions, it is very important to keep all traces as short as possible to reduce the effect of undesirable parasitic inductance. place input and output capacitors as close as possible to the device (no more than 5mm). in and out pins must be connected with short traces to the power bus. during normal operation, the power dissipation is small and the package temperature change is minimal. if the output is continuously shorted to ground at the maxi- mum supply voltage, the operation of the switches with the autoretry option does not cause problems because the total power dissipated during the short is scaled by the duty cycle: where v in = 5.5v, i out = 240ma, t blank = 14ms, and t retry = 98ms. attention must be given to the max4785 and max4787where the latch-off condition must be manually reset by toggling on from high to low. if the latch-off time dura- tion is not sufficiently high, it is possible for the device to reach the thermal-shutdown threshold and never be able to turn the device on until it cools down. p vi t tt mw max in max out max blank retry blank = + = __ 161 c it v max fwd min blank min in < __ 50ma/100ma current-limit switches 8 _______________________________________________________________________________________ load current switch status t blank t blank off on on pin voltage (a) (b) uvlo flag pin status load current switch status off on in pin voltage flag pin status t blank t blank figure 3. max4785/max4787 latch off fault blanking selector guide part current limit (ma) flag function auto- retry max4785exs 50 no no max4785exk 50 yes no max4786exs 50 no yes max4787exs 100 no no max4787exk 100 yes no max4788exs 100 no yes downloaded from: http:///
max4785?ax4788 50ma/100ma current-limit switches _______________________________________________________________________________________ 9 sc70, 4l.eps package outline, 4l sc70 21-0098 1 1 c package information (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/packages .) chip information transistor count: 1659process: bicmos downloaded from: http:///
max4785?ax4788 50ma/100ma current-limit switches 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. 10 ____________________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. package information (continued) (the package drawing(s) in this data sheet may not reflect the most current specifications. for the latest package outline information, go to www.maxim-ic.com/packages .) sc70, 5l.eps package outline, 5l sc70 21-0076 1 1 c downloaded from: http:///
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