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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. general description the MAX1773/MAX1773a highly integrated ics serve as the control logic for a system with multiple power sources. they directly drive external p-channel mosfets to select from an ac adapter and dual bat- tery sources for charge and discharge. the selection is made based on the presence of the power sources and the state of the batteries. the MAX1773/MAX1773a detect low battery conditions using integrated analog comparators and check for the presence of a battery by using battery thermistor outputs. the MAX1773/MAX1773a are designed for use with a buck topology charger. they provide a simple and easily controlled solution to a difficult analog power control prob- lem. the MAX1773/MAX1773a provide most of the power source monitoring and selection, freeing the system power management microprocessor (?) for other tasks. this not only simplifies development of the power management firmware for the ? but also allows the ? to enter standby, thereby reducing system power consumption. the MAX1773a is recommended for new designs. ________________________applications notebook and subnotebook computers pdas and handy-terminals internet tablets dual-battery portable equipment features patented ? 7-mosfet topology offers low-cost solution automatically detects and responds to: low battery voltage condition battery insertion and removal ac adapter presence direct drive of p-channel mosfets simplifies power management ? firmware extends battery life by allowing power management ? to enter standby 4.75v to 28v ac adapter input voltage range integrated ldo with 1ma drive capability small footprint 20-pin tssop package MAX1773/MAX1773a power source selector for dual-battery systems ________________________________________________________________ maxim integrated products 1 19-1796; rev 1; 1/03 evaluation kit available ordering information pin configuration appears at end of data sheet. part temp. range pin-package MAX1773 eup -40? to +85? 20 tssop MAX1773a eup -40? to +85? 20 tssop ? covered by u.s. patent number 5,764,032. MAX1773 MAX1773a tcomp minv v dd thmb batb chgb chga batstat batsel system logic supply ac adapter input 3.3v bata coma disa comb disb thma extld pds acdet acpres 3.3v battery a battery b output system load input 3.3v dc-dc converter output input step-down charger from host p to host p typical operating circuit
MAX1773/MAX1773a power source selector for dual-battery systems 2 _______________________________________________________________________________________ absolute maximum ratings 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. v bata , v batb to gnd ............................................-0.3v to +20v v coma to gnd........................................-0.3v to (v bata + 0.3v) v comb to gnd........................................-0.3v to (v batb + 0.3v) v chga , v chgb , v extld , v acdet to gnd ..............-0.3v to +30v v pds , v disa , v disb to gnd ...................-0.3v to (v extld + 0.3v) v dd , v batsel , v acpres , v b atstat , v t comp , v minv to gnd.......................................................-0.3v to +6v v thma, v thmb (note 1)............................................ -0.3v to +6v continuous current out of thma, thmb............................20ma i acpres , i batstat sink current..........................................30ma continuous power dissipation (t a = +70?) 20-pin tssop (derate 7.0mw/? above +70?) ........560mw operating temperature ......................................-40? to +85? storage temperature ........................................-65? to +150? lead temperature (soldering, 10s) .................................+300? electrical characteristics (v bata = v batb = 16.8v, c vdd = 3.3?, v minv = 0.93v, v extld = v acdet = 28v, v tcomp = 3v, v thma = v thmb = 1.65v, v batsel = 0, c coma = c comb = c disa = c disb = c chga = c chgb = c pds = 5nf, t a = 0? to +85?, unless otherwise noted.) parameter conditions min typ max units extld supply voltage range v extld > v bata and v batb 4.75 28.00 v bata, batb supply voltage range 4.75 19.00 v v acdet = 28v 5 8 bata, batb quiescent current (current from the higher voltage supply) v bata = 4.75v to 19v, v batb = 4.75v to 19v, i vdd = 0 v acdet = 2.2v to v bata and v batb 40 70 a v acdet = 28v 5 8 bata, batb quiescent current (current from the lower voltage supply) v bata = 4.75v to 19v, v batb = 4.75v to 19v, i vdd = 0 v acdet = 2.2v to v bata and v batb 813 a v acdet = 28v, v extld = 28v 35 55 extld quiescent current v acdet = 2.2v to v bata and v batb, v extld = 16v 58 a linear regulator i vdd = 0 to 100a 3.234 3.3 3.367 v dd output voltage i vdd = 100a to 1ma 3.168 3.3 3.432 v v bata or v batb = 5v to 19v, v extld = 5v 1.0 v bata = v batb = 5v, v extld = 5v to 28v 1.0 v dd power-supply rejection ratio v bata , v batb , or v extld = 5v to 19v, sawtooth at 10v/s, other supplies = 12v 1 mv/v v dd undervoltage lockout hysteresis is typically 50mv 2.0 2.5 3.0 v comparators tcomp undervoltage lockout (note 2) 0 1.1 v thm_ input voltage range 0 5.5 v thm_ input leakage current v thm _ = 5.5v 0.1 100 na v thma = v thmb = 0 to 5.5v 0 5.5 tcomp input voltage range v thma = v thmb = 0 to 5.5v, v bata = v batb = v extld = 4.75v 0 4.3 v note 1: signals on thma and thmb below -0.3v are clamped by internal diodes limit forward diode current to maximum continuous current. when voltage on these pins is below -0.3v.
_______________________________________________________________________________________ 3 MAX1773/MAX1773a power source selector for dual-battery systems electrical characteristics (continued) (v bata = v batb = 16.8v, c vdd = 3.3f, v minv = 0.93v, v extld = v acdet = 28v, v tcomp = 3v, v thma = v thmb = 1.65v, v batsel = 0, c coma = c comb = c disa = c disb = c chga = c chgb = c pds = 5nf, t a = 0 c to +85 c, unless otherwise noted.) parameter conditions min typ max units tcomp input leakage current v tcomp = 5.5v 0.1 100 na thm_ to tcomp trip threshold thm_ falling with respect to tcomp -30 +30 mv thm_ to tcomp hysteresis 15 50 mv acdet operating voltage range (note 3) 2.2 28.0 v acdet logic threshold high 2.2 v v acdet = 3v, v acdet < v bata and v batb 48 v acdet = 3v, v acdet < v batb , v bata = 0 5 9 acdet input bias current v acdet = 28v, v acdet > v bata and v batb 611 a acdet to bata trip threshold v acdet falling with respect to v bata 0 50 100 mv acdet to bata hysteresis 100 150 200 mv acdet to batb trip threshold v acdet falling with respect to v batb 0 50 100 mv acdet to batb hysteresis 100 150 200 mv minv operating voltage range v bata = v batb = 5 v minv 0.93 2.60 v minv input bias current v minv = 0.93v to 2.6v -100 +100 na v minv = 0.93v 4.55 4.65 4.75 bat_ minimum voltage trip threshold v bat _ falling v minv = 2.6v 12.7 13 13.3 v batsel input low voltage typical hysteresis is 100mv 0.8 v batsel input high voltage 2.0 v batsel input leakage current v batsel = 5.5v 1 a batsel action delay 20 100 s gate drivers com_ initial source current v bat _ = 16.8v, v com _ = 14.8v 5 ma v bat _ = 16.8v, v com _ = 16.4v 10 com_ final source current v bat _ = 16.8v, v com _ = 14.8v 50 100 150 a com_ sink current (pmos turn-on) v com _ = 11.8v, v bat _ = 16.8v (note 4) 4 ma v bat _ = 8v to 19v -11.5 -9.5 -7.5 com_ turn-on clamp voltage (v com _ to v bat _) v bat _ = 4.75v to 8v -8.00 -4.25 v pds source current (pmos turn-off) v pds = 10v, v extld = 12v 5 ma pds sink current (pmos turn-on) v pds = 2v to 28v 0.8 1.0 1.2 ma pds leakage current (pmos off) v pds = 28v 0.1 2 a chg_ sink current (pmos turn-on) v chg _ = 2v to 22v 0.7 1.0 1.3 ma chg_ leakage current (pmos off) v chg _ = 28v 0.1 2 a dis_ initial source current v extld = 15v, v dis _ = 13v 5 ma v extld = 15v, v dis _ = 14.6v 10 dis_ final source current v extld = 15v, v dis _ = 13v 50 100 150 a dis_ sink current (pmos turn-on) v extld = 16.8v, v dis _ = 11.8v (note 5) 4 ma
MAX1773/MAX1773a power source selector for dual-battery systems 4 _______________________________________________________________________________________ electrical characteristics (continued) (v bata = v batb = 16.8v, c vdd = 3.3f, v minv = 0.93v, v extld = v acdet = 28v, v tcomp = 3v, v thma = v thmb = 1.65v, v batsel = 0, c coma = c comb = c disa = c disb = c chga = c chgb = c pds = 5nf, t a = 0 c to +85 c, unless otherwise noted.) parameter conditions min typ max units v extld = 8v to 28v -11.5 -9.5 -7.5 dis_ turn-on clamp voltage (v dis _ to v extld ) v extld = 4.75v to 8v -8.00 -4.25 v status outputs v acpres = 0.4v 1 acpres sink current v acpres = 5.5v 30 ma v batstat = 0.4v 1 batstat sink current v batstat = 5.5v ma acpres leakage current v acpres = 5.5v 0.1 1 a batstat leakage current v batstat = 5.5v 0.1 1 a transition times battery switchover delay v acdet = 2.2v, v minv = 0.93v (note 6) 5 s battery action delay v acdet = 2.2v, v minv = 0.93v (note 7) 260 s thermistor action delay v acdet = 2.2v, v minv = 0.93v (note 8) 12 s ac to battery switchover delay v acdet = 2.2v, v minv = 0.93v (note 9) 10 s battery to ac switchover delay v acdet = 2.2v, v minv = 0.93v (note 10) 260 s chg_ turn-on delay (note 11) 130 300 530 s electrical characteristics (v bata = v batb = 16.8v, c vdd = 3.3f, v minv = 0.93v, v extld = v acdet = 28v, v tcomp = 3v, v thma = v thmb = 1.65v, v batsel = 0, c coma = c comb = c disa = c disb = c chga = c chgb = c pds = 5nf, t a = -40 c to +85 c, unless otherwise noted.) parameter conditions min typ max units extld supply voltage range v extld > v bata and v batb 4.75 28.00 v bata, batb supply voltage range 4.75 19.00 v v acdet = 28v 8 bata, batb quiescent current (current from the higher voltage supply) v bata = 4.75v to 19v, v batb = 4.75v to 19v, i vdd = 0 v acdet = 2.2v to v bata and v batb 70 a v acdet = 28v 8 bata, batb quiescent current (current from the lower voltage supply) v bata = 4.75v to 19v, v batb = 4.75v to 19v, i vdd = 0 v acdet = 2.2v to v bata and v batb 13 a v acdet = 28v, v extld = 28v 55 extld quiescent current v ac de t = 2.2v to v bata and v batb , v e x tld = 16v 8 a linear regulator i vdd = 0 to 100a 3.234 3.367 v dd output voltage i vdd = 100a to 1ma 3.168 3.432 v v bata or v batb = 5v to 19v, v extld = 5v 1.0 v dd power-supply rejection ratio v bata = v batb = 5v, v extld = 5v to 28v 1.0 mv/v v dd undervoltage lockout hysteresis is typically 50mv 2.0 3.0 v comparators tcomp undervoltage lockout (note 2) 0 1.1 v
_______________________________________________________________________________________ 5 MAX1773/MAX1773a power source selector for dual-battery systems electrical characteristics (continued) (v bata = v batb = 16.8v, c vdd = 3.3f, v minv = 0.93v, v extld = v acdet = 28v, v tcomp = 3v, v thma = v thmb = 1.65v, v batsel = 0, c coma = c comb = c disa = c disb = c chga = c chgb = c pds = 5nf, t a = -40 c to +85 c, unless otherwise noted.) parameter conditions min typ max units thm_ input voltage range 0 5.5 v thm_ input leakage current v thm_ = 5.5v 100 na v thma = v thmb = 0 to 5.5v 0 5.5 tcomp input voltage range v bata = v batb = v extld = 4.75v 0 4.3 v acdet operating voltage range (note 3) 2.2 28.0 v acdet logic threshold high 2.2 v v acdet = 3v, v acdet < v bata and v batb 8 v acdet = 3v, v acdet < v batb , v bata = 0 9 acdet input bias current v acdet = 28v, v acdet > v bata and v batb 11 a acdet to bata trip threshold v acdet falling with respect to v bata -35 +125 mv acdet to bata hysteresis 100 200 mv acdet to batb trip threshold v acdet falling with respect to v batb -35 +125 mv acdet to batb hysteresis 100 200 mv minv operating voltage range v bata = v batb = 5 v minv 0.93 2.60 v minv input bias current v minv = 0.93v to 2.6v -100 +100 na v minv = 0.93v 4.55 4.75 bat_ minimum voltage trip threshold v bat _ falling v minv = 2.6v 12.7 13.3 v batsel input low voltage typical hysteresis is 100mv 0.8 v batsel input high voltage 2.0 v batsel input leakage current v batsel = 5.5v 1 a batsel action delay 20 100 s gate drivers com_ initial source current v bat _ = 16.8v, v com _ = 14.8v 4 ma v bat _ = 16.8v, v com _ = 16.4v 10 com_ final source current v bat _ = 16.8v, v com _ = 14.8v 50 150 a com_ sink current (pmos turn-on) v com _ = 11.8v, v bat _ = 16.8v (note 4) 2 ma v bat _ = 8v to 19v -11.5 -7.25 com_ turn-on clamp voltage (v com _ to v bat _) v bat _ = 4.75v to 8v -8.00 -4.25 v pds source current (pmos turn-off) v pds = 10v, v extld = 12v 4 ma pds sink current (pmos turn-on) v pds = 2v to 28v 0.7 1.3 ma pds leakage current (pmos off) v pds = 28v 2 a chg_ sink current (pmos turn-on) v chg _ = 2v to 22v 0.6 1.4 ma
6 _______________________________________________________________________________________ MAX1773/MAX1773a power source selector for dual-battery systems note 2: tcomp undervoltage lockout sets the MAX1773/MAX1773a s internal status bits for the batteries to be designated as absent (v thm_ > v tcomp ). note 3: v acdet must remain above 2.2v, except in power-up. note 4: coma cannot sink current until v comb > v batb - 2v. likewise, comb cannot sink current until v coma > v bata - 2v. note 5: disa cannot sink current until v disb > v extld - 2v. likewise, disb cannot sink current until v disa > v extld - 2v. note 6: battery switchover delay starts when either v com_ or v dis_ of the connected battery begins to rise and ends when both v com_ and v dis_ of the other battery have fallen 3v below their sources (figures 1 and 2). note 7: battery action delay starts when the connected battery s voltage falls below 5 ? v minv and ends when both v com_ and v dis_ of the other battery have fallen 3v below their sources (figures 1 and 2). note 8: thermistor action delay begins when v thm_ of the connected battery rises above v tcomp and ends when both v com _ and v dis_ of the other battery have fallen 3v below their sources (figures 3 and 4). note 9: ac to battery switchover delay begins when v acdet falls below its threshold and ends when both v com_ and v dis_ of the battery being switched to have fallen 3v below their sources (figure 5). note 10: battery to ac switchover delay begins when v acdet rises above its threshold and ends when v dis_ of the battery being switched from has begun to rise (figure 6). note 11: chg_ turn-on delay begins when v chg_ of the battery being switched from begins to rise and ends when v chg_ of the battery being switched to begins to fall (figures 7 and 8). electrical characteristics (continued) (v bata = v batb = 16.8v, c vdd = 3.3f, v minv = 0.93v, v extld = v acdet = 28v, v tcomp = 3v, v thma = v thmb = 1.65v, v batsel = 0, c coma = c comb = c disa = c disb = c chga = c chgb = c pds = 5nf, t a = -40 c to +85 c, unless otherwise noted.) dis_ sink current (pmos turn-on) v extld = 16.8v, v dis_ = 11.8v (note 5) 2 ma v extld = 8v to 28v -11.50 -7.25 dis_ turn-on clamp voltage (v dis _ to v extld ) v extld = 4.75v to 8v -8.00 -4.25 v status outputs v acpres = 0.4v 1 acpres sink current v acpres = 5.5v 30 ma v batstat = 0.4v 1 batstat sink current v batstat = 5.5v 30 ma acpres leakage current v acpres = 5.5v 1 a batstat leakage current v batstat = 5.5v 1 a transition times battery switchover delay v acdet = 2.2v, v minv = 0.93v (note 6) 5 s battery action delay v acdet = 2.2v, v minv = 0.93v (note 7) 260 s thermistor action delay v acdet = 2.2v, v minv = 0.93v (note 8) 12 s ac to battery switchover delay v acdet = 2.2v, v minv = 0.93v (note 9) 10 s battery to ac switchover delay v acdet = 2.2v, v minv = 0.93v (note 10) 260 s chg_ turn-on delay (note 11) 130 530 s
_______________________________________________________________________________________ 7 MAX1773/MAX1773a power source selector for dual-battery systems typical operating characteristics (t a = +25 c, unless otherwise noted.) 0.04 -0.04 -0.08 -0.12 515 10 20 25 30 v dd error vs. input voltage MAX1773-01 v in (v) error (%) v in = v acdet , bat_ = open v in = v bat _, v acdet = 3.3v 0 0.01 1 10 i dd (ma) 0.1 v dd error vs. i dd MAX1773-02 0 -1 -2 -3 error (%) -2.5 -1.5 -2.0 -0.5 -1.0 0.5 -40 10 -15 35 60 85 v dd error vs. temperature MAX1773-03 temperature ( c) v dd error (%) i dd = 1ma i dd = 5 a 0 0 2 6 4 8 10 08 4121620 MAX1773-04 v battery _ (v) i battery _ ( a) total current from the battery battery current vs. battery voltage (v acdet = 20v) 15v v batb 5 ? v minv 2v 5v 15v 5v v extld v bata 12v transition from battery a to battery b (minv) (i extld = 1a, c extld = 66 f) MAX1773-05 100 s/div v bata = 12v, battery a removed at 100 s v batb = 10.75v v minv = 1.4v 5v 0 0 0 5v v coma v comb v disa v disb 10v 10v 0 transition from battery a to battery b (minv) (i extld = 1a, c extld = 66 f) MAX1773-06 5 s/div v bata = 12v v batb = 10.75v
MAX1773/MAX1773a power source selector for dual-battery systems 8 _______________________________________________________________________________________ typical operating characteristics (continued) (t a = +25 c, unless otherwise noted.) 12v v thma v extld 4v 11v 0 transition from battery a to battery b (tcomp) (i extld = 4a, c extld = 66 f) MAX1773-07 10 s/div v bata = 10.5v at 4a v batb = 12v at 4a v extld v batsel transition from battery a to battery b (batsel) (i extld = 4a, c extld = 66 f) MAX1773-09 50 s/div v bata = 9.4v at 4a v batb = 10.8v at 4a 11v 4v 10v 0 v disb v disa v comb v coma transition from battery a to battery b (t comp ) (i extld = 4a, c extld = 66 f) MAX1773-08 5 s/div v bata = 10.5v at 4a v batb = 12v at 4a 10v 10v 0 0 0 10v 10v 0 v extld v disa transition from ac adapter to battery a (i extld = 4a, c extld = 66 f) MAX1773-10 20 s/div v bata = 10.8v at 4a v acadapter = 17.5v at 4a 20v 10v 20v 10v 0 v acdet v bata v disa v chga transition from transition from battery a to ac adapter (i extld = 4a, c extld = 66 f) MAX1773-11 100 s/div v acadapter = 17.5a at 4a v bata = 10.5v at 4a v acadapter applied at 240 s charger input open 10a 0 10v 10v -10a 12v 10v 0 i bata (current from the battery) v bata 0
_______________________________________________________________________________________ 9 MAX1773/MAX1773a power source selector for dual-battery systems pin description pin name function 1 bata battery a connection 2 thma thermistor a input 3 chga open-drain gate driver for charge path mosfet to battery a 4 disa gate driver for discharge path mosfet to battery a. switches from v extld to (v extld - 9.5v). 5 coma gate driver for common path mosfet to battery a. switches from v bata to (v bata - 9.5v). 6 gnd ground 7 minv minimum operating voltage set point. the battery voltage switchover set point is 5 v minv . 8 extld external load connection. source connection for the pds, disa, and disb mosfets. 9 pds gate driver for the ac adapter mosfet 10 acdet ac adapter detection input 11 batstat open-drain battery status output. use a pullup resistor to the system logic supply. 12 acpres open-drain ac presence output. use a pullup resistor to the system logic supply. 13 batsel battery select digital input. selects which battery to charge or discharge. 14 tcomp externally set thermistor trip point. sets the thermistor voltage level for detecting the battery s presence. 15 v dd linear regulator output 16 comb gate driver for common path mosfet to battery b. switches from v batb to (v batb - 9.5v). 17 disb gate driver for discharge path mosfet to battery b. switches from v extld to (v extld - 9.5v). 18 chgb open-drain gate driver for charge path mosfet to battery b 19 thmb thermistor b input 20 batb battery b connection
10 ______________________________________________________________________________________ MAX1773/MAX1773a power source selector for dual-battery systems transition time diagrams (v com_gs = com_ turn-on clamp voltage, v dis_gs = dis_ turn-on clamp voltage, v charger = system step-down charger output.) v disa v disb v bata v coma v comb MAX1773-fig-01 battery action delay battery switchover delay v thma < v tcomp v thmb < v tcomp 5 ? v minv v bata v bata + v com_gs v extld + v dis_gs v extld + v dis_gs v batb + v com_gs v extld 3v 3v v batb v extld v disb v disa v batb v comb v coma MAX1773-fig-02 battery action delay battery switchover delay v thma < v tcomp v thmb < v tcomp 5 ? v minv v batb v bata v extld v batb + v com_gs v extld + v dis_gs v extld + v dis_gs v bata + v com_gs v extld 3v 3v figure 1. battery delay (battery a to battery b) figure 2. battery delay (battery b to battery a) v disa v disb v thma v coma v comb MAX1773-fig-03 thermistor action delay battery switchover delay v thmb < v tcomp v tcomp v bata v batb v extld v bata + v com_gs v extld + v dis_gs v extld + v dis_gs v batb + v com_gs v extld 3v 3v figure 3. thermistor switchover delay (battery a to battery b) v disb v disa v thmb v comb v coma MAX1773-fig-04 thermistor action delay battery switchover delay v thma < v tcomp v tcomp v batb v bata v extld v batb + v com_gs v extld + v dis_gs v extld + v dis_gs v bata + v com_gs v extld 3v 3v figure 4. thermistor switchover delay (battery b to battery a)
______________________________________________________________________________________ 11 MAX1773/MAX1773a power source selector for dual-battery systems v batsel MAX1773-fig-07 chg_ turn-on delay v chga v chgb v thma < v tcomp v thmb < v tcomp v charger v charger figure 7. charge turn-on delay (battery a to battery b) v batsel MAX1773-fig-08 chg_ turn-on delay v chgb v chga v thma < v tcomp v thmb < v tcomp v charger v charger figure 8. charge turn-on delay (battery b to battery a) v dis _ v acdet MAX1773-fig-05 ac to battery switchover delay v bat _ > 5 ? v minv v thm _ < v tcomp a cdet to bat_ trip threshold v extld + v dis_gs v extld 3v figure 5. ac to battery switchover delay v dis _ v acdet MAX1773-fig-06 battery to ac switchover delay v bat _ > 5 ? v minv v thm _ < v tcomp a cdet to bat_ trip threshold v extld v extld + v dis_gs figure 6. battery to ac switchover delay transition time diagrams (continued) (v com_gs = com_ turn-on clamp voltage, v dis_gs = dis_ turn-on clamp voltage, v charger = system step-down charger output.)
MAX1773/MAX1773a power source selector for dual-battery systems 12 ______________________________________________________________________________________ detailed description the MAX1773/MAX1773a provide the functions neces- sary to allow an external controller to manage the power connections needed for two battery packs, an ac adapter input, a battery charger, and the system load. the MAX1773/MAX1773a use seven pmos fets to provide all the switching necessary in systems using a step-down charger powered by the ac adapter (figures 9 and 10). the MAX1773/MAX1773a automati- cally adapt to many transient conditions such as ac plug-in, battery hot swapping, and battery switchover to provide constant power to the system without requir- ing real-time support from an external controller. the MAX1773/MAX1773a draw their power from the highest voltage supply present (figure 11). battery detection the MAX1773/MAX1773a monitor the battery s thermis- tor voltage to determine the presence of the battery. the devices compare the battery s thermistor voltage (v thm_ ) to the thermistor trip point (v tcomp ). if v thm_ < v tcomp , then the MAX1773/MAX1773a assume that the battery is present. however, if v thm_ > v tcomp , the MAX1773/MAX1773a assume that the battery is absent and do not charge or discharge the battery. modes of operation the MAX1773/MAX1773a provide three modes of oper- ation. start-up states mode provides functionality when the MAX1773/MAX1773a are initially powered by a bat- tery when no ac adapter is present. ac adapter states mode provides functionality when an ac adapter is pre- sent. standard battery states mode provides functionality when one or both batteries are present, the ac adapter is not present, and extld is above 2.2v. the standard battery states mode requires an external supply with an output voltage between 2.2v and 4.5v for acdet, as shown in figure 10. the external power supply must be powered from extld. ac adapter states the MAX1773/MAX1773a check for the presence of an ac adapter by sensing the voltage at acdet. when v acdet exceeds the batteries voltage and 4.75v, then the MAX1773/MAX1773a use the ac adapter to power the load. in addition, if the selected battery is present, the MAX1773/MAX1773a connect the selected battery s charge path. see table 1 for a detailed listing of the MAX1773/MAX1773a states for operation with an ac adapter detected. standard battery states when the ac adapter power supply is not present, the MAX1773/MAX1773a use the batteries to supply the load. batsel allows an external controller to select a battery. table 2 shows the simplified standard battery states that normally control operation. however, the battery switchover latch, the low-battery latch, and the discharged battery latch are able to suspend the state table and provide additional functionality. batsel battery a battery b batstat connection state 0 present x 0 ac adapter is connected to load. battery a s charge path connected. 0 absent x 1 ac adapter is connected to load. 1 x present 1 ac adapter is connected to load. battery b s charge path connected. 1 x absent 0 ac adapter is connected to load. table 1. ac adapter states x = don t care, present: v thm_ < v tcomp, absent: v thm_ > v tcomp, acpres = 0 batsel battery a vbata battery b vbatb batstat connection state 0 present >5 v minv x x 0 battery a is connected to the load. x present >5 v minv absent x 0 battery a is connected to the load. x present >5 v minv x < 5 v minv 0 battery a is connected to the load. x x <5 v minv present > 5 v minv 1 battery b is connected to the load. x absent x present > 5 v minv 1 battery b is connected to the load. 1 x x present > 5 v minv 1 battery b is connected to the load. table 2. simplified standard battery states (without latches) x = don t care, present: v thm_ < v tcomp , absent: v thm_ > v tcomp
______________________________________________________________________________________ 13 MAX1773/MAX1773a power source selector for dual-battery systems system step-down charger chgb chga r12 r14 coma disa comb disb pds v batb+ v bata+ extld power connections ac-adapter supply figure 9. 7-mosfet topology the battery switchover latch stops the MAX1773/ MAX1773a from oscillating when the device switches from the selected battery and then the selected bat- tery s voltage recovers. according to the state table, the MAX1773/MAX1773a would switch back to the selected battery as soon as the battery s voltage recovered. the battery switchover latch suspends the state table as soon as the MAX1773/MAX1773a switch over to the nonselected battery. this causes the MAX1773/MAX1773a to continue to power from the nonselected battery unless the latch is cleared. the battery switchover latch is cleared when batsel is toggled (to select the other battery), when in the startup states mode, in the ac adapter states mode, and when the selected battery is removed (v thm_ > v tcomp ). to prevent the MAX1773/MAX1773a from switching to a discharged battery, the low-battery latch suspends the state table when the unconnected battery s voltage is below 5 ? v minv and the discharging battery s voltage drops below 5 ? v minv . instead of switching to the unconnected battery, the MAX1773/MAX1773a continue to power from the discharging battery. this latch is cleared when the unconnected battery is removed (v thm_ > v tcomp ), when in the startup states mode, when in the ac adapter states mode, and if the uncon- nected battery s voltage rises above 5 ? v minv . the discharged battery latch sets whenever the MAX1773/MAX1773a are in the standard battery states mode, both batteries are present (v thm_ < v tcomp ), one of the batteries is low (v bat_ < 5 ? v minv ), and the other battery s voltage is below v acdet . while the v bata v batb battery a battery b connection state >5 v minv x present x battery a is connected to the load. <5 v minv >5 v minv present present battery b is connected to the load. x >5 v minv absent present battery b is connected to the load. x x absent absent no connections. <5 v minv <5 v minv x x no connections. <5 v minv x x absent no connections. x <5 v minv absent x no connections. table 3. startup states x = don t care, present: v thm_ < v tcomp , absent: v thm_ > v tcomp
14 ______________________________________________________________________________________ MAX1773/MAX1773a discharged battery latch is set, the state table is sus- pended, the MAX1773/MAX1773a are not allowed to switch batteries, and the low battery latch is cleared. the discharged battery latch is cleared when both batteries are above v acdet, in the ac adapter states mode, and in the startup states mode. startup states when v acdet rises at startup, the MAX1773/ MAX1773a use startup states. see table 3 for a detailed listing of the MAX1773/MAX1773a states in this mode. note that once acdet rises above 2.2v, the MAX1773/MAX1773a are no longer in the startup power source selector for dual-battery systems MAX1773 MAX1773a tcomp minv v dd thmb batb chgb chga batstat batsel system logic supply ac adapter input 3.3v bata coma disa comb disb thma extld pds acdet acpres 3.3v battery a battery b output system load input 3.3v dc-dc converter output input step-down charger 0.1 f 100k ? 3.3k ? 10k ? 500k ? 500k ? 28.7k ? 100k ? 10k ? 10k ? 100k ? 0.33 f from host p to host p 1.5 f 66 f 1.5 f r14 8k ? r12 8k ? r13 8k ? p1 p4 p7 figure 10. standard application circuit
______________________________________________________________________________________ 15 MAX1773/MAX1773a power source selector for dual-battery systems states mode and enters either the standard battery states mode or the ac adapter states mode. status and configuration batstat and acpres provide information to an exter- nal controller. table 4 shows the different states of batstat and acpres . in the ac adapter states mode, the batsel action delay (see electrical characteristics ) allows the exter- nal controller to tell if both batteries are absent. when both batteries are absent in the ac adapter states mode and batsel changes states, batstat is imme- diately updated. however, changes to the connection states are delayed (see table 1 for connection states). MAX1773 MAX1773a tcomp minv v dd v dd thmb batb chgb chga batstat batsel bata comb 9.5v 9.5v 9.5v 9.5v uvlo disa coma disb thma gnd extld pds acdet acpres + _ + _ + _ + _ linear regulator + _ delay 60 s + _ logic figure 11. functional diagram
MAX1773/MAX1773a power source selector for dual-battery systems 16 ______________________________________________________________________________________ if batsel is returned to its original state within the batsel action delay, then changes to the connection states are never made. note that in the standard battery states mode and in the ac adapter states mode when one or both batteries are present, both batstat and the connection states are delayed during the batsel update delay. mosfet drivers to minimize the time when no supply is connected to the external load during switchover transients, the MAX1773/MAX1773a use active pullup drivers for the discharge paths (dis_) and the common paths (com_). when the MAX1773/MAX1773a initially begin to pull up one of these pins, they use a large current (initial com_ source current and initial dis_ source current; see electrical characteristics ). once the com_ voltage rises to within 2v of v bat_ or the dis_ voltage rises to within 2v of v extld, then a weaker dri- ver is used to hold up the voltage (final com_ source current and final dis_ source current; see electrical characteristics ). the MAX1773/MAX1773a are designed to prevent shoot-through from one battery to the other when transi- tioning from discharging one battery to discharging the other battery. to accomplish this, the MAX1773/ MAX1773a do not connect the second battery to extld until it senses that the first battery is disconnect- ed from extld. see notes 4 and 5 of electrical characteristics . to allow flexibility when choosing the higher voltage pds pmos fet (p7, figure 10), the MAX1773/ MAX1773a do not limit the gate-to-source voltage applied to the pds pmosfet. the minimum v gs is set by the MAX1773/MAX1773a pds sink current (see electrical characteristics ) and the external resistor from pds to extld (r13): v gs(min) = -i pds(sink) ? r pds where v gs(min) is the minimum p7 gate-to-source voltage, i pds(sink) is the pds sink current, and r pds is r13. the MAX1773/MAX1773a use open-collector drivers to open the charge paths. minimize the value of the pullup resistors on the charge paths (r12 and r14) to allow the MAX1773/MAX1773a to quickly turn on the pmos fets; however, keep the value large enough to prevent a lower v gs than specified by the pmos fet. the mini- mum v gs is: v gs(min) = -i chg_(sink) ? r chg_ where v gs(min) is the minimum p1 or p4 gate-to-source voltage, i chg_(sink) is the chg_ sink current (see electrical characteristics ), and r chg_ is r12 or r14. v dd regulator the MAX1773/MAX1773a feature an internal linear reg- ulator to provide power for itself and external circuitry. the linear regulator s output is available at v dd and is nominally 3.3v. when the linear regulator is not used to power external circuitry, bypass it with a 0.33f ceram- ic capacitor. to supply external loads up to 1ma, bypass the linear regulator with a 3.3f tantalum capacitor. applications information load switchover transients when power switches from one power source to anoth- er, a transient is created on the load. this transient ( ? v extld ) is minimized by the capacitance on the load (c extld ). the voltage transient can be approximated as: where t switchover is the time where no supply is con- nected to the extld. ? v it c extld exltld switchover extld = mode status batstat acpres all v dd undervoltage lockout 1 1 startup states 11 standard battery states selected battery discharge path connected batsel 1 standard battery states other battery discharge path connected batsel 1 ac adapter states selected battery charge path connected batsel 0 ac adapter states selected battery absent batsel 0 table 4. status bits
______________________________________________________________________________________ 17 MAX1773/MAX1773a power source selector for dual-battery systems in applications where the battery voltage always falls away slowly, t switchover is primarily composed of the battery switchover delay. however, in applications where the battery voltage can suddenly fall away, t switchover is substantially increased because it is primarily composed of the battery action delay (figures 1 and 2). ideally, when a battery is removed from the system, the thermistor connection is broken before the battery s power path is broken. in this case, t switchover is typi- cally bound by the thermistor action delay (figures 3 and 4). however, if the battery s power path is broken first, then t switchover primarily consists of the shorter of the following times: time until the thermistor connec- tion is broken plus the thermistor action delay, or the battery action delay. source switchover transients when the MAX1773/MAX1773a suddenly switch a power supply to the load, they create a current transient from the source to charge up the capacitance on the load. the peak current drawn is approximated by: where ? v extload is the voltage difference between the supply switched off and the supply switched on, r source is the source resistance of the power supply switched on, r switch is the r ds(on) of the pmos fets in the path, and r esr is the equivalent series resistance of the output capacitance. the duration of the current transient is determined by r source , r switch , r esr , and the output capacitance. smaller resistances and less output capacitance reduce the transient duration. typical operation figure 12 shows a typical discharge and charge cycle for a system utilizing the MAX1773/MAX1773a, two 3-cell lithium-ion (li+) batteries, and a 20v ac adapter power supply. the diagram starts with the ac adapter applied, no batteries present, and battery a selected (see ac adapter states ). batstat = batsel = 1 indi- cates that battery a is not present and battery a s i pk extload source switch esr v rrr = ++ ? ac present, no batteries, a selected bata inserted batb inserted ac adapter removed v bata falls below 5 ? v minv external controller reacts v batb falls below 5 ? v minv , system shuts down ac adapter applied external controller reacts v acdet v batb v bata t 0 t 1 t 2 t 3 t 4 t 5 t 6 t 7 t 8 t 9 v extld batsel 0 0 1 0 0 0 0 0 0 0 1 0 0 1 1 1 1 1 1 1 0 1 0 1 0 0 0 0 0 0 acpres 20v 3.3v 20v 8v 12.6v 8v 12.6v 8v batstat figure 12. charge/discharge example
MAX1773/MAX1773a power source selector for dual-battery systems 18 ______________________________________________________________________________________ charge path is not connected. if the external controller polled the MAX1773/MAX1773a as described in status and configuration , then batstat would return batsel (0) to indicate that battery b is not present. at t 1 , battery a is inserted and the MAX1773/ MAX1773a connect battery a s charge path. note that batstat changes to batsel (0) to indicate that bat- tery a is present. at t 2 , battery b is inserted. batstat does not change and still indicates that battery a is present. at t 3 , the ac adapter is removed and the MAX1773/MAX1773a automatically disconnect battery a s charge path and connect battery a s discharge path (see standard battery states ). acpres changes to 1 to indicate that the ac adapter source is no longer present. batstat = batsel (0) to indicate that battery a is present and supplying the load. between t 3 and t 4 , battery a discharges as it supplies the load. at t 4 , battery a s voltage falls below 5 ? v min, and the MAX1773/MAX1773a automatically disconnect battery a s discharge path and connect battery b s discharge path. batstat goes to batsel (1) to indicate that bat- tery a is no longer supplying the load. shortly after batstat goes high, the external controller should catch up to the MAX1773/MAX1773a and change batsel. this is shown at t 5 . batstat remains at 1, indicating that battery b is present and supplying the load. at t 6 , battery b falls below 5 ? v min, and the MAX1773/MAX1773a automatically disconnect battery b s discharge path and connect battery a s discharge path. batstat changes to batsel (0) to indicate that battery b is no longer supplying the load. at this point, the external controller orders a controlled shutdown of the system and drastically reduces the supply current. at t 7 , the ac adapter supply is reconnected to the sys- tem. the MAX1773/MAX1773a automatically discon- nect battery a s discharge path, connects the ac adapter s load path (pds switch), and connects battery b s charge path. batstat goes to batsel (1) to indi- cate that battery b is present. acpres goes to 0 to indicate that the ac adapter source is present. at t 8 , the external controller recognizes that battery b is charged and changes batsel to battery a. batstat goes to batsel (0) to indicate that battery a is present. after t 9 , the batteries are fully charged and the system is ready for another cycle. power mosfet selection the MAX1773/MAX1773a do not place stringent requirements on the external pmos fets. use pmos fets with low v gs thresholds (logic level fets). low r ds(on) pmos fets are desirable since the pmos fet s resistance directly contributes to power losses. also, ensure that the pmos fet s v ds and v gs ratings exceed the specific circuit requirements. see table 5 for a list of recommended manufacturers. layout guidelines the MAX1773/MAX1773a do not use fast switching times or high frequencies. therefore, the layout require- ments are minimal. keep the gate connections to the external pmos fets short to minimize capacitive cou- pling, reduce parasitic inductance, and ensure stability. in addition, minimize the power path length when pos- sible to reduce the path s resistance. see the MAX1773 evaluation kit for a layout example. supplier phone fax fairchild 408-822-2000 408-822-2102 ir 310-322-3331 310-322-3332 siliconix 408-988-8000 408-970-3950 table 5. recommended manufacturers 20 19 18 17 16 15 14 13 1 2 3 4 5 6 7 8 batb thmb chgb disb disa chga thma bata top view comb v dd tcomp batsel extld minv gnd coma 12 11 9 10 acpres batstat acdet pds MAX1773 MAX1773a tssop pin configuration chip information transistor count: 5245 process: bicmos
______________________________________________________________________________________ 19 differences between MAX1773 and MAX1773a this section discusses the differences between the MAX1773 and MAX1773a for the situations detailed. note that the MAX1773 and MAX1773a are pin-to-pin compatible. pds fet switching MAX1773: if battery b is selected but absent, and bat- tery a is inserted with a voltage less than five times minv, when an adapter is inserted, the pds fet does not turn on. the problem also occurs if battery a is selected but absent, and battery b is inserted with a voltage less than five times minv, when an adapter is inserted, the pds fet does not turn on. in the MAX1773a, when the sequences discussed are encountered, the part has been changed to enable the pds fet. this results in the pds fet having to dissi- pate less energy in the MAX1773a. selected battery present but under-voltage MAX1773: when the selected battery is present and less than five times the minv voltage, and a battery above five times the minv voltage is inserted at the nonselected slot. in this case, the MAX1773 will not enable discharge from the nonselected slot if the thm_ pin of the nonselected battery is valid after the tcomp pin goes high. in the MAX1773a the order in which the thm_ and tcomp pins become enabled is unimportant for these states. this results in this behavior not being encoun- tered in the MAX1773a. switchover to nonselected battery upon adapter removal MAX1773: when the selected battery is present and less than five times minv, and the nonselected battery is present and greater than five times minv. the MAX1773 enables the discharge path from the non- selected battery, which has a voltage greater than five times minv, which is an expected operation for the part. if the ac adapter is then inserted, the charge path to the selected battery is enabled, this is also expected operation. when the adapter is removed, the MAX1773 does not switch to the nonselected battery, which is the issue. in the MAX1773a, when the ac adapter is removed in the scenario detailed, three separate conditions are possible: 1) a charger is present but does not charge the selected battery. this can happen if the input cur- rent-limit feature in the charger has been activated, reducing the charger current to zero. the ac adapter is then removed. in this case the MAX1773a allows discharge from the unselected battery, whose voltage was above 5 x minv. 2) a charger is present and charges the selected bat- tery. the battery is charged sufficiently so that it can support the system load for more then 10ms. (assuming the typical application circuit with 100k ? and 0.1f on the ac adapter input.) when the ac adapter is removed, the MAX1773a correct- ly allows discharge from the selected battery. 3) in the third scenario, the charger charges the selected battery, but before the battery is sufficient- ly charged to support the system load, the ac adapter is removed. in this case, the MAX1773a does not allow discharge from the unselected bat- tery, whose voltage is above 5 x minv. the limiting condition is that the battery has to be sufficiently charged to support the system load for 10ms. MAX1773/MAX1773a power source selector for dual-battery systems
MAX1773/MAX1773a power source selector for dual-battery systems 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. 20 ____________________maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ? 2003 maxim integrated products printed usa is a registered trademark of maxim integrated products. tssop4.40mm.eps 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 .)

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