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MAX8730 low-cost battery charger ________________________________________________________________ maxim integrated products 1 19-3885; rev 0; 12/05 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. evaluation kit available general description the MAX8730 highly integrated, multichemistry, battery- charger control ic simplifies construction of accurate and efficient chargers. the MAX8730 operates at high switching frequency to minimize external component size and cost. the MAX8730 uses analog inputs to con- trol charge current and voltage, and can be pro- grammed by a microcontroller or hardwired. the MAX8730 reduces charge current to give priority to the system load, effectively limiting the adapter current and reducing the adapter current requirements. the MAX8730 provides a digital output that indicates the presence of an ac adapter, and an analog output that monitors the current drawn from the ac adapter. based on the presence and absence of the ac adapter, the MAX8730 automatically selects the appro- priate source for supplying power to the system by con- trolling two external switches. under system control, the MAX8730 allows the battery to undergo a relearning cycle in which the battery is completely discharged through the system load and then recharged. an analog output indicates adapter current or battery- discharge current. the MAX8730 provides a low-quies- cent-current linear regulator, which may be used when the adapter is absent, or disabled for reduced current consumption the MAX8730 is available in a small, 5mm x 5mm, 28- pin, thin (0.8mm) qfn package. an evaluation kit is available to reduce design time. the MAX8730 is available in a lead-free package. applications notebook computers tablet pcs portable equipment with rechargeable batteries features ? small inductor (3.5?) ? programmable charge current > 4.5a ? automatic power-source selection ? analog inputs control charge current and charge voltage ? monitor outputs for ac adapter current battery-discharge current ac adapter presence ? independent 3.3v 20ma linear regulator ? up to 17.6v (max) battery voltage ? +8v to +28v input voltage range ? reverse adapter protection ? system short-circuit protection ? cycle-by-cycle current limit ordering information part temp range pin- package pkg code MAX8730eti+ -40? to +85? 28 thin qfn (5mm x 5mm) t2855-5 + denotes lead-free package. pin configuration appears at end of data sheet. MAX8730 adapter input pds src asns acin acok vctl ldo cls ictl mode refon inpon ldo relth ref swref batt csin csip dhi pdl dhiv iinp ccv cci ccs cssp cssn gnd ref host system load battery t ypical operating circuit
MAX8730 low-cost battery charger 2 _______________________________________________________________________________________ absolute maximum ratings electrical characteristics (circuit of figure 1. v src = v asns = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v vctl = v ictl = 1.8v, mode = float, acin = 0, cls = ref, refon = ldo, inpon = ldo, relth = 2v. t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25?.) 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. cssp, src, acok , asns, dhiv, batt, csip to gnd.......................................................-0.3v to +30v csip to csin or cssp to cssn ............................-0.3v to +0.3v dhiv to src .................................................-6v to (src + 0.3v) dhi to dhiv ...............................................-0.3v to (src + 0.3v) pdl, pds to gnd ........................................-0.3v to (src + 0.3) cci, ccs, ccv, iinp, swref, ref, mode, acin to gnd.............................-0.3v to (ldo + 0.3v) relth, vctl, ictl, refon, cls, ldo, inpon to gnd .....................................................-0.3v to +6v ldo short-circuit current...................................................50ma continuous power dissipation (t a = +70?) 28-pin tqfn (derate 20.8mw/? above +70?) .......1667mw operating temperature range ...........................-40? to +85? junction temperature ............................................................+ 150? storage temperature range .............................-60? to +150? lead temperature (soldering, 10s) .................................+300? parameter symbol conditions min typ max units charge-voltage regulation vctl range 0 3.6 v not including resistor tolerances -1.0 +1.0 v vctl = 3.6v or 0v including 1% resistor tolerances -1.05 +1.05 battery-regulation voltage accuracy v vctl = v ldo (3 or 4 cells) -0.5 +0.5 % v vctl default threshold v vctl rising 4.4 v v vctl = 3v 0 4 vctl input bias current src = batt, asns = gnd inpon = refon = 0, v vctl = 5v 0 16 ? charge-current regulation ictl range 0 3.6 v 128.25 135 141.75 mv v ictl = 3.6v -5 +5 % 71.25 75 78.75 mv full-charge-current accuracy (csip to csin) v i ctl = 2.0v -5 +5 % trickle-charge-current accuracy v ictl = 120mv 2.5 4.5 7.5 mv charge-current gain error based on v ictl = 3.6v and v ictl = 0.12v -1.9 +1.9 % charge-current offset error based on v ictl = 3.6v and v ictl = 0.12v -2 +2 mv batt/csip/csin input voltage range 0 19 v charging enabled 300 600 csip/csin input current charging disabled, src = batt, asns = gnd or v ictl = 0v 8 16 ?
MAX8730 low-cost battery charger _______________________________________________________________________________________ 3 electrical characteristics (continued) (circuit of figure 1. v src = v asns = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v vctl = v ictl = 1.8v, mode = float, acin = 0, cls = ref, refon = ldo, inpon = ldo, relth = 2v. t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25?.) parameter symbol conditions min typ max units ictl falling 50 65 80 ictl power-down mode threshold ictl rising 70 90 110 mv v ictl = 3v -1 +1 ictl input bias current src = batt, asns = gnd, v ictl = 5v -1 +1 ? cssp-to-cssn full-scale current-sense voltage 72.75 75.75 78.75 mv 72.75 75.75 78.75 mv v cls = ref (trim point) -4 +4 % 50 53 56 mv v cls = ref x 0.7 -5.6 +5.6 % 36 38 40.5 mv input current-limit accuracy v cls = ref x 0.5 -6.6 +6.6 % cssp/cssn input voltage range 8.0 28 v v cssp = v cssn = v src > 8.0v 400 800 cssp/cssn input current v src = 0v 0.1 1 ? cls input range 1.1 ref v cls input bias current v cls = 2.0v -1 +1 ? iinp transconductance v cssp - v cssn = 56mv 2.66 2.8 2.94 ?/mv v cssp - v cssn = 100mv, v iinp = 0 to 4.5v -5 +5 v cssp - v cssn = 75mv -8 +8 v cssp - v cssn = 56mv -5 +5 iinp accuracy v cssp - v cssn = 20mv -12.5 +12.5 % iinp gain error based on v ic t l = re f x 0. 5 and v ic t l = re f -7 +7 % iinp offset error based on v ic t l = re f x 0. 5 and v ic t l = re f -2 +2 mv iinp fault threshold iinp rising 4.1 4.2 4.3 v supply and linear regulator src input voltage range 8.0 28 v src falling 7 7.4 src undervoltage lockout threshold src rising 7.5 8 v
MAX8730 low-cost battery charger 4 _______________________________________________________________________________________ electrical characteristics (continued) (circuit of figure 1. v src = v asns = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v vctl = v ictl = 1.8v, mode = float, acin = 0, cls = ref, refon = ldo, inpon = ldo, relth = 2v. t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25?.) parameter symbol conditions min typ max units normal mode 4 6 ma v inpon = v refon = low 10 20 v inpon = low, v refon = high 300 600 v inpon = high, v refon = low 300 600 src quiescent current (inpon/refon = don? care) v src = v batt = 12v, asns = gnd (note 2) v inpon = v refon = high 350 600 ? v batt = 16.8v, v src = 19v, ictl = 0 8 16 batt input current v batt = 2v to 19v, v src > v batt + 0.3v 300 600 ? i csip + i csin + i batt , asns = gnd 2 5 v refon = 5.4v 300 600 battery-leakage current i csip + i csin + i batt + i cssp + i cssn + i src , asns = refon = gnd inpon = gnd 2 5 ? ldo output voltage 8.0v < v src < 28v, no load 5.2 5.35 5.5 v ldo load regulation 0 < i ldo < 10ma 20 50 mv ldo undervoltage lockout threshold v src = 8.0v 4 v references ref output voltage ref 4.18 4.20 4.22 v ref undervoltage lockout threshold ref falling 3.1 3.9 v swref output voltage 8.0v < v src < 28v, no load 3.234 3.3 3.366 v swref load regulation 0.1ma < i swref < 20ma 20 50 mv trip points acin threshold acin rising 2.037 2.1 2.163 v acin threshold hysteresis 60 mv acin input bias current v acin = 2.048v -1 +1 ? switching regulator dhi off-time v batt = 16.0v 300 350 400 ns dhi off-time k factor v batt = 16.0v 4.8 5.6 6.4 v x ? sense voltage for minimum discontinuous mode ripple current v csip - v csin 7 mv cycle-by-cycle current-limit sense voltage 160 200 240 mv charge disable threshold v src - v batt , src falling 40 60 80 mv dhiv output voltage with respect to src -4.3 -4.8 -5.5 v dhiv sink current 10 ma
MAX8730 low-cost battery charger _______________________________________________________________________________________ 5 electrical characteristics (continued) (circuit of figure 1. v src = v asns = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v vctl = v ictl = 1.8v, mode = float, acin = 0, cls = ref, refon = ldo, inpon = ldo, relth = 2v. t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25?.) parameter symbol conditions min typ max units dhi resistance low i dhi = -10ma 2 4 ? dhi resistance high i dhi = 10ma 1 2 ? error amplifiers v c tl = 3.6v , v bat t = 16.8v , m od e = ld o 0.0625 0.125 0.250 gmv loop transconductance v c tl = 3.6v , v bat t = 12.6v , m od e = float 0.0833 0.167 0.333 ma/v gmi loop transconductance ictl = 3.6v, v cssp - v csin = 75mv 0.5 1 2 ma/v gms loop transconductance v cls = 2.048v, v cssp - v cssn = 75mv 0.5 1 2 ma/v cci/ccs/ccv clamp voltage 1.1v < v ccv < 3.0v, 1.1v < v cci < 3.0v, 1.1v < v ccs < 3.0v 150 300 600 mv logic levels mode, refon input low voltage 0.5 v mode input middle voltage 1.9 2.65 3.3 v m od e , re fon inp ut h i g h v ol tag e 3.4 v mode, refon, inpon input bias current mode = 0 or 3.6v -2 +2 ? v inpon rising 2.2 v inpon threshold v inpon falling 0.8 v adapter detection acok voltage range 0 28 v acok sink current v acok = 0.4v, acin = 1.5v 1 ma acok leakage current v acok = 28v, acin = 2.5v 1 ? battery detection v mode = v ldo +140 batt overvoltage threshold v vctl = v ldo , batt rising; result with respect to battery-set voltage v mode = float +100 mv batt overvoltage hysteresis 100 mv relth operating voltage range 0.9 2.6 v relth input bias current v relth = 0.9v to 2.6v -50 +50 na v relth = 0.9v 4.42 4.5 4.58 batt minimum voltage trip threshold v batt falling v relth = 2.6v 12.77 13.0 13.23 v pds, pdl switch control adapter-absence detect threshold v asns - v batt , v asns falling -300 -280 -240 mv adapter-detect threshold v asns - v batt -140 -100 -60 mv pds output low voltage result with respect to src, i pds = 0 -8 -10 -12 v pds/pdl output high voltage result with respect to src, i pd_ = 0 -0.2 -0.5 v pds/pdl turn-off current v pds = v src - 2v, v src = 16v 6 12 ma
MAX8730 low-cost battery charger 6 _______________________________________________________________________________________ electrical characteristics (continued) (circuit of figure 1. v src = v asns = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v vctl = v ictl = 1.8v, mode = float, acin = 0, cls = ref, refon = ldo, inpon = ldo, relth = 2v. t a = 0? to +85? , unless otherwise noted. typical values are at t a = +25?.) electrical characteristics (circuit of figure 1. v src = v asns = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v vctl = v ictl = 1.8v, mode = float, acin = 0, cls = ref, refon = ldo, inpon = ldo, relth = 2v. t a = -40? to +85? , unless otherwise noted.) parameter symbol conditions min typ max units pds turn-on current pds = src 6 12 ma pdl turn-on resistance pdl = gnd 50 100 200 k ? pds/pdl delay time 5.0 ? parameter symbol conditions min typ max units charge-voltage regulation vctl range 0 3.6 v not including resistor tolerances -1.2 +1.2 v vctl = 3.6v or 0v including 1% resistor tolerances -1.25 +1.25 battery-regulation-voltage accuracy v vctl = v ldo (3 or 4 cells) -0.8 +0.8 % v vctl default threshold v vctl rising 4.4 v vctl input bias current src = batt, asns = gnd inpon = refon = 0, v vctl = 5v 0 16 ? charge-current regulation ictl range 0 3.6 v 128.25 141.75 mv v ictl = 3.6v -5 +5 % 70 80 mv full-charge-current accuracy (csip to csin) v ictl = 2.0v -6.7 +6.7 % trickle-charge-current accuracy v ictl = 120mv 2 10 mv charge-current gain error based on v ictl = 3.6v and v ictl = 0.12v -1.9 +1.9 % charge-current offset error based on v ictl = 3.6v and v ictl = 0.12v -2 +2 mv batt/csip/csin input voltage range 0 19 v charging enabled 1000 csip/csin input current charging disabled, src = batt, asns = gnd, or v ictl = 0v 16 ? ictl falling 50 80 ictl power-down mode threshold ictl rising 70 110 mv
MAX8730 low-cost battery charger _______________________________________________________________________________________ 7 parameter symbol conditions min typ max units input-current regulation cssp-to-cssn full-scale current-sense voltage 72.75 78.25 mv v cls = ref (trim point) 72.75 78.25 mv v cls = ref x 0.7 50.0 56.0 mv input current-limit accuracy v cls = ref x 0.5 36.00 40.50 mv cssp/cssn input voltage range 8.0 28 v cssp/cssn input current v cssp = v cssn = v src > 8.0v 1000 ? cls input range 1.1 ref v iinp transconductance v cssp - v cssn = 56mv 2.66 2.94 ?/mv v cssp - v cssn = 100mv, v iinp = 0 to 4.5v -5 +5 v cssp - v cssn = 75mv -8 +8 v cssp - v cssn = 56mv -5 +5 iinp accuracy v cssp - v cssn = 20mv -12.5 +12.5 % iinp gain error based on v i c t l = re f x 0.5 and v i c t l = re f -7 +7 % iinp offset error based on v i c t l = re f x 0.5 and v i c t l = re f -2 +2 mv iinp fault threshold iinp rising 4.1 4.3 v supply and linear regulator src input voltage range 8.0 28 v src falling 7 src undervoltage lockout threshold src rising 8 v normal mode 6 ma v inpon = v refon = low 20 v inpon = low, v refon = high 600 v inpon = high, v refon = low 600 src quiescent current (inpon/refon = don? care) src = v batt = 12v, asns = gnd (note 2) v inpon = v refon = high 600 ? batt input current v batt = 2v to 19v, v src > v batt + 0.3v 600 ? v refon = 5.4v 600 battery leakage current i csip + i csin + i batt + i cssp + i cssn + i src , asns = refon = gnd inpon = gnd 16 ? ldo output voltage 8.0v < vsrc < 28v, no load 5.2 5.5 v ldo load regulation 0 < i ldo < 10ma 50 mv electrical characteristics (continued) (circuit of figure 1. v src = v asns = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v vctl = v ictl = 1.8v, mode = float, acin = 0, cls = ref, refon = ldo, inpon = ldo, relth = 2v. t a = -40? to +85? , unless otherwise noted.)
MAX8730 low-cost battery charger 8 _______________________________________________________________________________________ parameter symbol conditions min typ max units references ref output voltage ref 0 < i ref < 500? 4.16 4.24 v ref undervoltage lockout threshold ref falling 3.9 v swref output voltage 8.0v < v src < 28v, no load 3.224 3.376 v swref load regulation 0.1ma < i swref < 20ma 50 mv trip points acin threshold acin rising 2.037 2.163 v switching regulator dhi off-time v batt = 16.0v 300 400 ns dhi off-time k factor v batt = 16.0v 4.8 6.4 v x ? cycle-by-cycle current-limit sense voltage 160 240 mv dhiv output volatge with respect to src -4.3 -5.5 v dhiv sink current 10 ma dhi resistance low i dhi = -10ma 4 ? dhi resistance high i dhi = 10ma 2 ? error amplifiers v c tl = 3.6v , v bat t = 16.8v , m od e = ld o 0.0625 0.250 gmv loop transconductance v c tl = 3.6v , v bat t = 12.6v , m od e = float 0.0833 0.333 ma/v gmi loop transconductance ictl = 3.6v, v cssp - v csin = 75mv 0.5 2 ma/v gms loop transconductance v cls = 2.048v, v cssp - v cssn = 75mv 0.5 2 ma/v cci/ccs/ccv clamp voltage 1.1v < v ccv < 3.0v, 1.1v < v cci < 3.0v, 1.1v < v ccs < 3.0v 150 600 mv logic levels m od e , re fon inp ut low v ol tag e 0.5 v mode input middle voltage 1.9 3.3 v m od e , re fon inp ut h i g h v ol tag e 3.4 v v inpon rising 2.2 inpon threshold v inpon falling 0.8 v adapter detection acok voltage range 0 28 v acok sink current v acok = 0.4v, acin = 1.5v 1 ma electrical characteristics (continued) (circuit of figure 1. v src = v asns = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v vctl = v ictl = 1.8v, mode = float, acin = 0, cls = ref, refon = ldo, inpon = ldo, relth = 2v. t a = -40? to +85? , unless otherwise noted.)
MAX8730 low-cost battery charger _______________________________________________________________________________________ 9 note 1: accuracy does not include errors due to external-resistance tolerances. note 2: in this mode, src current is drawn from the battery. parameter symbol conditions min typ max units battery detection relth operating voltage range 0.9 2.6 v v relth = 0.9v 4.42 4.58 batt minimum voltage trip threshold v batt falling v relth = 2.6v 12.77 13.23 v pds, pdl switch control adapter-absence-detect threshold v asns - v batt , v asns falling -310 -240 mv adapter-detect threshold v asns - v batt -140 -60 mv pds output low voltage result with respect to src, i pds = 0 -7 -12 v pds/pdl output high voltage result with respect to src, i pd_ = 0 -0.5 v pds/ pdl turn-off current v pds = v src - 2v, v src = 16v 6 ma pds turn-on current pds = src 6 ma pdl turn-on resistance pdl = gnd 50 100 200 k ? electrical characteristics (continued) (circuit of figure 1. v src = v asns = v cssp = v cssn = 18v, v batt = v csip = v csin = 12v, v vctl = v ictl = 1.8v, mode = float, acin = 0, cls = ref, refon = ldo, inpon = ldo, relth = 2v. t a = -40? to +85? , unless otherwise noted.)
MAX8730 low-cost battery charger 10 ______________________________________________________________________________________ t ypical operating characteristics (circuit of figure 1, adapter = 19.5v, v batt = 12v, v ictl = 2.4v, mode > 1.8v, refon = inpon = ldo, v relth = v ref /2, t a = +25?, unless otherwise noted.) trickle-charge current vs. battery voltage battery voltage (v) trickle-charge-current error (%) MAX8730 toc07 0369121518 -25 -20 -15 -10 -5 0 5 10 15 20 25 charge current = 150ma battery-voltage error vs. charge current charge current (a) battery-voltage error (%) MAX8730 toc08 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 -0.25 -0.20 -0.15 -0.10 -0.05 0 4 cells 3 cells battery-voltage error vs. vctl vctl (v) charge-voltage error (%) MAX8730 toc09 0 1.5 0.5 1.0 2.0 2.5 3.0 3.5 -1.0 -0.8 -0.6 -0.4 -0.2 0 0.2 0.4 0.6 0.8 1.0 input current-limit error vs. cls v cls (v) input current-limit error (%) MAX8730 toc01 1.1 1.6 2.1 2.6 3.1 3.6 4.1 -15 -10 -5 0 5 10 15 typical unit minimum maximum input current-limit error vs. system current system current (a) input current-limit error (%) 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 v in = 17v v in = 19v v in = 24v v cls = v ref x 0.7 input current-limit error vs. system current system current (a) input current-limit error (%) MAX8730 toc03 012345 0 1 2 3 4 5 6 7 v cls = v ref / 2 v cls = v ref x 0.7 v cls = v ref iinp error vs. v cssp - v cssn MAX8730 toc04 v cssp - v cssn iinp error (%) 90 80 70 60 50 40 30 20 10 -10 -5 0 5 10 15 -15 0 100 minimum maximum charge-current error vs. charge-current setting v ictl (v) charge-current error (%) MAX8730 toc05 0 0.6 1.2 1.8 2.4 3.0 3.6 -20 -15 -10 -5 0 5 10 15 20 typical unit minimum error maximum error charge-current error vs. battery voltage battery voltage (v) charge-current error (%) MAX8730 toc06 0510 15 20 -0.5 -0.2 0.1 0.4 0.7 1.0 1.3 1.6 v ictl = 2v v ictl = 3.6v
MAX8730 low-cost battery charger ______________________________________________________________________________________ 11 output ripple voltage vs. battery voltage battery voltage (v) output ripple voltage (mv p-p ) MAX8730 toc10 0510 15 20 0 0.03 0.06 0.09 0.12 0.15 0.18 t ypical operating characteristics (continued) (circuit of figure 1, adapter = 19.5v, v batt = 12v, v ictl = 2.4v, mode > 1.8v, refon = inpon = ldo, v relth = v ref /2, t a = +25?, unless otherwise noted.) switching frequency vs. battery voltage battery voltage (v) switching frequency (khz) MAX8730 toc11 0369121518 200 400 600 800 1000 battery removal MAX8730toc12 13v 12.5v c out = 4.7 f c out = 10 f 4 s/div charge current = 12v adapter insertion MAX8730toc13 0v 20v 20v 0v 20v 0v 20v 0v 100 s/div adapter pds pdl system load adapter insertion adapter removal MAX8730toc14 0v 20v 20v 0v 20v 0v 20v 0v 4ms/div adapter pds pdl system load battery voltage = 16.8v system load transient MAX8730toc15 0a 5a 5a 0a 5a 0a 500mv/div 200 s/div load current adapter current inductor current compensation ccs cci ccs cci
MAX8730 low-cost battery charger 12 ______________________________________________________________________________________ t ypical operating characteristics (continued) (circuit of figure 1, adapter = 19.5v, v batt = 12v, v ictl = 2.4v, mode > 1.8v, refon = inpon = ldo, v relth = v ref /2, t a = +25?, unless otherwise noted.) charge current vs. time time (h) charge current (a) MAX8730 toc20 0 0.5 1.0 1.5 2.0 2.5 3.0 0 0.5 1.0 1.5 2.0 2.5 3.0 3.5 initial condition: 4 cells 10v battery full charge = 16.8v ldo load regulation i ldo (ma) ldo error (%) MAX8730 toc21 0102 0304050 -0.9 -0.8 -0.6 -0.4 -0.2 -0.7 -0.5 -0.3 -0.1 0 charger disabled battery leakage current vs. battery voltage battery voltage (v) battery-leakage current ( a) MAX8730 toc19 0369121518 0 100 200 300 400 500 refon = inpon = 1 refon = 0 inpon = 1 refon = 1 inpon = 0 refon = inpon = 0 adapter quiescent current vs. adapter voltage adapter voltage (v) adapter quiescent current (ma) MAX8730 toc18 0510 15 20 25 0 0.5 1.0 1.5 2.0 2.5 3.0 battery absent refon = 1 inpon = 1 refon = 0 inpon = 0 peak-to-peak inductor current vs. battery voltage battery voltage (v) peak-to-peak inductor current (a) max7830 toc16 0369121518 0.5 0.9 0.7 1.1 1.5 1.3 1.7 1.9 2.1 2.3 2.5 efficiency vs. charge current charge current (a) efficiency (%) MAX8730 toc17 0 1.0 2.0 3.0 3.5 0.5 1.5 2.5 4.0 60 70 80 90 100 4 cells 3 cells
MAX8730 low-cost battery charger ______________________________________________________________________________________ 13 ldo line regulation input voltage (v) ldo error (%) MAX8730 toc22 813182 328 -0.400 -0.390 -0.380 -0.370 -0.360 -0.350 -0.395 -0.385 -0.375 -0.365 -0.355 ref error vs. temperature temperature ( c) ref error (%) MAX8730 toc24 -40 -20 0 20 40 60 80 -0.35 -0.30 -0.25 -0.20 -0.15 -0.10 -0.05 0 reference load regulation i ref ( a) ref (%) MAX8730 toc23 0 100 200 300 400 500 -0.25 -0.23 -0.21 -0.19 -0.17 -0.15 -0.13 -0.11 charger disabled swref load regulation swref output current (ma) swref error (%) MAX8730 toc25 010203 040 -1.5 -1.2 -0.9 -0.6 -0.3 0 swref voltage vs. temperature temperature ( c) swref voltage (v) MAX8730 toc26 -40 -20 0 20 40 60 80 3.25 3.26 3.27 3.28 3.29 3.30 3.31 3.32 discontinuous mode switching waveform MAX8730toc27 0 0 0 20v lx dhi inductor current 20v 1a 1 s/div charge current = 20ma t ypical operating characteristics (continued) (circuit of figure 1, adapter = 19.5v, v batt = 12v, v ictl = 2.4v, mode > 1.8v, refon = inpon = ldo, v relth = v ref /2, t a = +25?, unless otherwise noted.)
MAX8730 low-cost battery charger 14 ______________________________________________________________________________________ pin name function 1 asns adapter voltage sense. when v asns > v batt - 280mv, the battery switch is turned off and the adapter switch is turned on. connect to the adapter input using an rc filter as shown in figure 1. 2 ldo linear-regulator output. ldo is the output of the 5.35v linear regulator supplied from src. bypass ldo with a 1? ceramic capacitor from ldo to gnd. 3 swref 3.3v switched reference. swref is a 1% accurate linear regulator that can deliver 20ma. swref remains active when the adapter is absent and may be disabled by setting refon to zero. bypass swref with a 1? capacitor to gnd. 4 ref 4.2v voltage reference. bypass ref with a 1? capacitor to gnd. 5 cls source current-limit input. voltage input for setting the current limit of the input source. 6 acin ac-adapter-detect input. acin is the input to an uncommitted comparator. acin does not influence adapter and battery selection. 7 vctl charge-voltage-control input. connect vctl to ldo for default 4.2v/cell. 8 relth relearn threshold for relearn mode. in relearn mode, when v batt < 5 x v relth , the MAX8730 drives pds low and drives pdl high to terminate relearning of a discharged battery. see the relearn mode section for more details. 9 acok ac detect output. this open-drain output pulls low when acin is greater than ref/2 and asns is greater than batt - 100mv. the acok output is high impedance when the MAX8730 is powered down. connect a 10k ? pullup resistor from ldo to acok . 10 mode tri-level input for setting number of cells or asserting the conditioning mode: mode = gnd; asserts relearn mode. mode = float; charge with 3 times the cell voltage programmed at vctl. mode = ldo; charge with 4 times the cell voltage programmed at vctl. 11 iinp input-current-monitor output. iinp sources the current proportional to the current sensed across cssp and cssn. the transconductance from (cssp ?cssn) to iinp is 2.8?/mv (typ). 12 ictl charge-current-control input. pull ictl to gnd to shut down the charger. 13 refon swref enable. drive refon high to enable swref. 14 inpon input current-monitor enable. drive inpon high to enable iinp. 15 cci output current-regulation loop compensation point. connect a 0.01? capacitor from ccs to gnd. 16 ccv v ol tag e- reg ul ati on loop c om p ensati on p oi nt. c onnect a 10k ? r esi stor i n ser i es w i th a 0.01? cap aci tor to g n d . 17 ccs input current-regulation loop compensation point. connect a 0.01? capacitor from ccs to gnd. 18 gnd analog ground 19 batt battery-voltage feedback input 20 csin charge-current-sense negative input 21 csip charge-current-sense positive input. connect a current-sense resistor from csip to csin. 22 dhiv high-side driver supply. connect a 0.1? capacitor from dhiv to cssn. 23 dhi high-side power mosfet driver output. connect to high-side, p-channel mosfet gate. 24 src dc supply input voltage and connection for driver for pds/pdl switches. bypass src to power ground with a 1? capacitor. 25 cssn input current sense for negative input 26 cssp input current sense for positive input. connect a 15m ? current-sense resistor from cssp to cssn. 27 pds power-source pmos switch driver output. when the adapter is absent, the pds output is pulled to src through an internal 1m ? resistor. 28 pdl system-load pmos switch driver output. when the adapter is absent, the pdl output is pulled to ground through an internal 100k ? resistor. 29 backside paddle backside paddle. connect the backside paddle to analog ground. pin description
MAX8730 low-cost battery charger ______________________________________________________________________________________ 15 MAX8730 adapter input rs1 15m ? c2 10nf r6 6k ? r4 75k ? r5 18k ? c1 32nf r10 15k ? c3 1 f r3 3k ? r12 50k ? r13 50k ? c11 1 f r9 10k ? r8 50k ? r7 37.4k ? ref ldo c in1 4.7 f l1 3.5 h rs2 30m ? c12 0.1 f c4 0.1 f c6 0.1 f c8 0.01 f r11 10k ? c7 0.01 f c9 0.01 f c10 1 f c out1 4.7 f c out2 4.7 f p2 p1 p4 d1 p3 r2 r1 pds src asns acin ictl acok mode swref vctl cls refon inpon ldo relth ref batt csin csip dhi pdl dhiv iinp ccv cci c5 1 f ccs gnd cssp input ref input host output output a/d input ldo ref cssn system load battery c out figure 1. typical application circuit
MAX8730 low-cost battery charger 16 ______________________________________________________________________________________ detailed description the MAX8730 includes all the functions necessary to charge li+, nimh, and nicd batteries. a high-efficien- cy, step-down, dc-dc converter is used to implement a precision constant-current, constant-voltage charger. the dc-dc converter drives a p-channel mosfet and uses an external free-wheeling schottky diode. the charge current and input current-sense amplifiers have low-input offset errors, allowing the use of small-value sense resistors for reduced power dissipation. figure 2 is the functional diagram. the MAX8730 features a voltage-regulation loop (ccv) and two current-regulation loops (cci and ccs). the loops operate independently of each other. the ccv voltage-regulation loop monitors batt to ensure that its voltage never exceeds the voltage set by vctl. the cci battery current-regulation loop monitors current delivered to batt to ensure that it never exceeds the current limit set by ictl. the charge-current-regulation loop is in control as long as the battery voltage is below the set point. when the battery voltage reaches its set point, the voltage-regulation loop takes control and maintains the battery voltage at the set point. a third loop (ccs) takes control and reduces the charge cur- rent when the adapter current exceeds the input cur- rent limit set by cls. the ictl, vctl, and cls analog inputs set the charge current, charge voltage, and input-current limit, respec- tively. for standard applications, default set points for vctl provide 4.2v per-cell charge voltage. the mode input selects a 3- or 4-cell mode. based on the presence or absence of the ac adapter, the MAX8730 provides an open-drain logic output sig- nal ( acok ) and connects the appropriate source to the system. p-channel mosfets controlled from the pdl and pds select the appropriate power source. the mode input allows the system to perform a battery relearning cycle. during a relearning cycle, the battery is isolated from the charger and completely discharged through the system load. when the battery reaches 100% depth of discharge, pdl turns off and pds turns on to connect the adapter to the system and to allow the battery to be recharged to full capacity. setting charge voltage the vctl input adjusts the battery output voltage, v batt . this voltage is calculated by the following equation: where cells is the number of cells selected with the mode input (see table 1). connect mode to ldo for 4- cell operation. float the mode input for 3-cell operation. the battery-voltage accuracy depends on the absolute value of vctl, and the accuracy of the resistive volt- age-divider that sets vctl. calculate the battery volt- age accuracy according to the following equation: where e 0 is the worst-case MAX8730 battery voltage error when using 1% resistors (0.83%), i vctl is the vctl input bias current (4?), and r vctl is the imped- ance at vctl. connect vctl to ldo for the default setting of 4.20v/cell with 0.7% accuracy. connect mode to gnd to enter relearn mode, which allows the battery to discharge into the system while the adapter is present; see the relearn mode section . setting charge current ictl sets the maximum voltage across current-sense resistor rs2, which determines the charge current. the full-scale differential voltage between csip and csin is 135mv (4.5a for rs2 = 30m ? ). set ictl according to the following equation: the input range for ictl is 0 to 3.6v. to shut down the charger, pull ictl below 65mv. choose a current-sense resistor (rs2) to have a sufficient power rating to handle the full-charge current. the current-sense voltage may be reduced to minimize the power dissipation. however, this can degrade accuracy due to the current-sense amplifier? input offset (?mv). see the typical operating characteristics to estimate the charge-cur- rent accuracy at various set points. the charge-current error amplifier (gmi) is compensated at the cci pin. see the compensation section. vixrsx v mv ictl chg . = 2 36 135 vex ixr batt error vctl vctl _ % =+ ? ? ? ? ? ? ? 0 100 36 1 v cells x v v batt vctl ( ) =+ 4 9 table 1. cell-count programming cells cell count gnd relearn mode float 3 ldo 4
MAX8730 low-cost battery charger ______________________________________________________________________________________ 17 n MAX8730 a = 20v/v cssn cssp current-sense amplifier current-sense amplifier gm = 2.8 a/mv iinp inpon ref system over- current cls gms ccs a = 15v/v csin csip cci gmi ictl 65mv charger shutdown cell- select logic batt mode ref selector (default = 4.2v) vctl gmv ccv lowest voltage clamp 222ma lvc 6.56a vctl + 40mv dhi high- side driver src dhiv ovp imin imax ccmp dc-dc converter 5.4v charger regulator src ldo reference 4.2v ref charger bias logic batt adapter detect reference 3.3v refon src swref ref/2 gnd acin acok csi -5v regulator src - 10v gnd rel_en src asns pds pdl logic pds batt pdl src relth cssp 6 a rel_en n figure 2. functional diagram
MAX8730 low-cost battery charger 18 ______________________________________________________________________________________ the MAX8730 includes a foldback feature, which reduces the schottky requirement at low battery volt- ages. see the foldback current section . setting input-current limit the total input current, from a wall adapter or other dc source, is the sum of the system supply current and the current required by the charger. when the input current exceeds the set input current limit, the MAX8730 decreases the charge current to provide priority to sys- tem load current. system current normally fluctuates as portions of the system are powered up or put to sleep. the input-current-limit circuit reduces the power requirement of the ac wall adapter, which reduces adapter cost. as the system supply rises, the available charge current drops linearly to zero. thereafter, the total input current can increase without limit. the total input current is the sum of the device supply cur- rent, the charger input current, and the system load cur- rent. the total input current can be estimated as follows: where is the efficiency of the dc-dc converter (typi- cally 85% to 95%). cls sets the maximum voltage across the current- sense resistor rs1, which determines the input current limit. the full-scale differential voltage between cssp and cssn is 75mv (5a for rs1 = 15m ? ). set cls according to the following equation: the input range for cls is 1.1v to v ref . choose a cur- rent-sense resistor (rs1) to have a sufficient power rat- ing to handle the full system current. the current-sense resistor may be reduced to improve efficiency, but this degrades accuracy due to the current-sense amplifier? input offset (?mv). see the typical operating charac- teristics to estimate the input current-limit accuracy at various set points. the input current-limit error amplifier (gms) is compensated at the ccs pin; see the com- pensation section. input-current measurement iinp monitors the system-input current sensed across cssp and cssn. the voltage of iinp is proportional to the input current according to the following equation: v iinp = i input x rs1 x g iinp x r 10 where i input is the dc current supplied by the ac adapter, g iinp is the transconductance of iinp (2.8?/mv typ), and r 10 is the resistor connected between iinp and ground. connect a 0.1? filter capacitor from iinp to gnd to reduce ripple. iinp has a 0 to 4.5v output-voltage range. connect iinp to gnd if it is not used. the MAX8730 provides a short-circuit latch to protect against system overload or short. the latch is set when v iinp rises above 4.2v, and disconnects the adapter from the system by turning pds off (pdl does not change). the latch is reset by bringing src below uvlo (remove and reinsert the adapter). choose a fil- ter capacitor that is large enough to provide appropri- ate debouncing and prevent accidental faults, yet results in a response time that is fast enough to ther- mally protect the mosfets. see the system short circuit section. iinp can be used to measure battery-discharge current (see figure 1) when the adapter is absent. to disable iinp and reduce battery consumption to 10?, drive inpon to low. charging is disabled when inpon is low, even if the adapter is present. ac-adapter detection and power-source selection the MAX8730 includes a hysteretic comparator that detects the presence of an ac power adapter and automatically selects the appropriate power source. when the adapter is present (v asns > v batt - -100mv) the battery is disconnected from the system load with the p-channel (p3) mosfet. when the adapter is removed (v asns < v batt - -270mv), pds turns off and pdl turns on with a 5s break-before- make sequence. the acok output can be used to indicate the presence of the adapter. when v acin > 2.1v and v asns > v batt - 100mv, acok becomes low. connect a 10k ? pullup resistor between ldo and acok . use a resistive volt- age-divider from the adapter? output to the acin pin to set the appropriate detection threshold. since acin has a 6v absolute maximum rating, set the adapter threshold according to the following equation: relearn mode the MAX8730 can be programmed to perform a relearn cycle to calibrate the battery? fuel gauge. this cycle consists of isolating the battery from the charger and dis- charging it through the system load. when the battery v v adapter threshold adapter max _ _ > 3 vixrsx v mv cls limit ref = 1 75 ii ixv vx input load charge battery in =+
MAX8730 low-cost battery charger ______________________________________________________________________________________ 19 reaches 100% depth of discharge, it is then recharged. connect mode to gnd to place the MAX8730 in relearn mode. in relearn mode, charging stops, pds turns off, and pdl turns on. to utilize relearn mode, there must be two source-con- nected mosfets to prevent the ac adapter from sup- plying current to the system through the p1? body diode. connect src to the common source node of two mosfets. the system must alert the user before performing a relearn cycle. if the user removes the battery during relearn mode, the MAX8730 detects battery removal and reconnects the ac adapter (pds turns on and pdl turns off). battery removal is detected when the battery falls below 5xrelth. ldo regulator, ref, and swref an integrated linear regulator (ldo) provides a 5.35v supply derived from src, and delivers over 10ma of load current. ldo biases the 4.2v reference (ref) and most of the control circuitry. bypass ldo to gnd with a 1? ceramic capacitor. an additional standalone 1%, 3.3v linear regulator (swref) provides 20ma and can remain on when the adapter is absent. set refon low to disable swref. set refon high for normal opera- tion. swref must be enabled to allow charging. operating conditions adapter present: the adapter is considered to be present when: v src > 8v (max) v asns > v batt - 300mv (max) charging: the MAX8730 allows charging when: v src - v csin > 100mv (typ) 3 or 4 cells selected (mode float or high condition) ictl > 110mv (max) inpon is high relearn mode: the MAX8730 enables relearn mode when: v batt / 5 > v relth mode is grounded dc-dc converter the MAX8730 employs a step-down dc-dc converter with a p-channel mosfet switch and an external schottky diode. the MAX8730 features a constant-cur- rent-ripple, current-mode control scheme with cycle-by- cycle current limit. for light loads, the MAX8730 operates in discontinuous conduction mode for improved efficiency. the operation of the dc-dc con- troller is determined by the following four comparators as shown in the functional block diagram in figure 3: ? the imin comparator sets the peak inductor current in discontinuous mode. imin compares the control signal (lvc) against 100mv (corresponding to 222ma when rs2 = 30m ? ). the comparator termi- nates the switch on-time when imin exceeds the threshold. ? the ccmp comparator is used for current-mode reg- ulation in continuous conduction mode. ccmp com- pares lvc against the charging-current feedback signal (csi). the comparator output is high and the mosfet on-time is terminated when the csi voltage is higher than lvc. ? the imax comparator provides a cycle-by-cycle cur- rent limit. imax compares csi to 2.95v (correspond- ing to 6.56a when rs2 = 30m ? ). the comparator output is high and the mosfet on-time is terminated when the current-sense signal exceeds 6.56a. a new cycle cannot start until the imax comparator output goes low. ? the ovp comparator is used to prevent overvoltage at the output due to battery removal. ovp compares batt against the set voltage; see the setting charge voltage section. when batt is 20mv x cells above the set value, ovp goes high and the mosfet on- time is terminated. imax ccmp imin ovp csi 2.95v 100mv vctl setpoint + 20mv batt/cells batt lvc r s q q off-time one-shot off-time compute dh driver figure 3. dc-dc converter block diagram
MAX8730 low-cost battery charger 20 ______________________________________________________________________________________ ccv, cci, ccs, and lvc control blocks the MAX8730 controls input current (ccs control loop), charge current (cci control loop), or charge voltage (ccv control loop), depending on the operating condi- tion. the three control loops?cv, cci, and ccs?re brought together internally at the lowest voltage clamp (lvc) amplifier. the output of the lvc amplifier is the feedback control signal for the dc-dc controller. the minimum voltage at the ccv, cci, or ccs appears at the output of the lvc amplifier and clamps the other control loops to within 0.3v above the control point. clamping the other two control loops close to the low- est control loop ensures fast transition with minimal overshoot when switching between different control loops (see the compensation section). continuous-conduction mode with sufficient charge current, the MAX8730? inductor current never crosses zero, which is defined as contin- uous-conduction mode. the controller starts a new cycle by turning on the high-side mosfet. when the charge-current feedback signal (csi) is greater than the control point (lvc), the ccmp comparator output goes high and the controller initiates the off-time by turning off the mosfet. the operating frequency is governed by the off-time, which depends upon v batt . at the end of the fixed off-time, the controller initiates a new cycle only if the control point (lvc) is greater than 100mv, and the peak charge current is less than the cycle-by-cycle current limit. restated another way, imin must be high, imax must be low, and ovp must be low for the controller to initiate a new cycle. if the peak inductor current exceeds the imax comparator threshold or the output voltage exceeds the ovp threshold, then the on-time is terminated. the cycle-by- cycle current limit protects against overcurrent and short-circuit faults. the MAX8730 computes the off-time by measuring v batt : t off = 5.6?/v batt for v batt > 4v. the switching frequency in continuous mode varies according to the equation: discontinuous conduction the MAX8730 operates in discontinuous conduction mode at light loads to make sure that the inductor cur- rent is always positive. the MAX8730 enters discontinu- ous conduction mode when the output of the lvc control point falls below 100mv. for rs2 = 30m ? , this corresponds to a peak inductor current of 222ma: the MAX8730 implements slope compensation in dis- continuous mode to eliminate multipulsing. this pre- vents audible noise and minimizes the output ripple. compensation the charge-voltage and charge current-regulation loops are compensated separately and independently at the ccv, cci, and ccs pins. ccv loop compensation the simplified schematic in figure 4 is sufficient to describe the operation of the MAX8730 when the volt- age loop (ccv) is in control. the required compensa- tion network is a pole-zero pair formed with c cv and r cv . the pole is necessary to roll off the voltage loop? response at low frequency. the zero is necessary to compensate the pole formed by the output capacitor and the load. r esr is the equivalent series resistance (esr) of the charger output capacitor (c out ). r l is the equivalent charger output load, where r l = ? v batt / ? i chg . the equivalent output impedance of the gmv i mv rs ma dis = = 1 2 100 15 2 111 f vx sx vv v src batt batt . = ? + ? ? ? ? ? ? 1 56 11 c cv c out r cv r l r esr r ogmv ccv batt gmv ref gm out figure 4. ccv loop diagram
MAX8730 low-cost battery charger ______________________________________________________________________________________ 21 name equation description ccv pole lowest frequency pole created by c cv and gmv? finite output resistance. since r ogmv is very large and not well controlled, the exact value for the pole frequency is also not well controlled (r ogmv > 10m ? ). ccv zero voltage-loop compensation zero. if this zero is at the same frequency or lower than the output pole f p_out , then the loop-transfer function approximates a single-pole response near the crossover frequency. choose c cv to place this zero at least 1 decade below crossover to ensure adequate phase margin. output pole output pole formed with the effective load resistance r l and output capacitance c out . r l influences the dc gain but does not affect the stability of the system or the crossover frequency. output zero output esr zero. this zero can keep the loop from crossing unity gain if f z_out is less than the desired crossover frequency; therefore, choose a capacitor with an esr zero greater than the crossover frequency. amplifier, r ogmv , is greater than 10m ? . the voltage amplifier transconductance, gmv = 0.125?/mv for 4 cells and 0.167?/mv for 3 cells. the dc-dc converter transconductance is dependent upon the charge cur- rent-sense resistor rs2: where a csi = 15v/v and rs2 = 30m ? in the typical application circuits, so gm out = 2.22a/v. the loop transfer function is given by: the poles and zeros of the voltage-loop transfer function are listed from lowest frequency to highest frequency in table 2. near crossover, c cv is much lower impedance than r ogmv . since c cv is in parallel with r ogmv, c cv domi- nates the parallel impedance near crossover. additionally r cv is much higher impedance than c cv and dominates the series combination of r cv and c cv , so: c out is typically much lower impedance than r l near crossover so the parallel impedance is mostly capaci- tive and: if r esr is small enough, its associated output zero has a negligible effect near crossover and the loop-transfer function can be simplified as follows: setting the ltf = 1 to solve for the unity-gain frequency yields: for stability, choose a crossover frequency lower than 1/5 the switching frequency. for example, choosing a crossover frequency of 45khz and solving for r cv using the component values listed in figure 1 yields r cv = 10k ? : r cf gmv gm k cv out co cv out _ = ? 2 10 ? fgmg r xc co cv out mv cv out _ = 2 ltf gm r sc g out cv out mv = r sc r sc l out l out ( ) 1 1 + ? rscr sc r r ogmv x cv cv cv ogmv cv ( ) ( ) 1 1 + + ? ltf gm r gmv r sc r sc r sc r sc r out l ogmv out esr cv cv cv ogmv out l ( )( ) ( )( ) = + + + + 11 11 gm ars out csi = 1 2 table 2. ccv loop poles and zeros f rc pcv ogmv cv _ = 1 2 f rc zcv cv cv _ = 1 2 f rc p out l out _ = 1 2 f rc z out esr out _ = 1 2
MAX8730 low-cost battery charger 22 ______________________________________________________________________________________ where: v batt = 16.8v gmv = 0.125?/mv gm out = 2.22a/v c out = 10? f osc = 350khz (minimum occurs at v in = 19v and v batt = 16.8v) r l = 0.2 ? f co-cv = 45khz to ensure that the compensation zero adequately can- cels the output pole, select f z_cv f p_out : c cv (r l / r cv ) c out c cv 200pf figure 5 shows the bode plot of the voltage-loop fre- quency response using the values calculated above. cci loop compensation the simplified schematic in figure 6 is sufficient to describe the operation of the MAX8730 when the bat- tery current loop (cci) is in control. since the output capacitor? impedance has little effect on the response of the current loop, only a simple single pole is required to compensate this loop. a csi is the internal gain of the current-sense amplifier. rs2 is the charge-current- sense resistor (30m ? ). r ogmi is the equivalent output impedance of the gmi amplifier, which is greater than 10m ? . gmi is the charge-current amplifier transcon- ductance = 1?/mv. gm out is the dc-dc converter transconductance = 2.22a/v. the loop transfer function is given by: that describes a single-pole system. since: the loop-transfer function simplifies to: the crossover frequency is given by: for stability, choose a crossover frequency lower than 1/10 of the switching frequency: values for c ci greater than 10 times the minimum value may slow down the current-loop response. choosing c ci = 10nf yields a crossover frequency of 15.9khz. figure 7 shows the bode plot of the current-loop fre- quency response using the values calculated above. c x gmi xc nf ci ci >= 10 2 4 f gmi c co ci ci _ = 2 ltf gmi r sr c ogmi ogmi ci = + 1 gm ars out csi = 1 ltf gm a rs gmi r sr c out csi ogmi ogmi ci = + 1 frequency (hz) magnitude (db) phase (degrees) 100k 10k 1k 100 10 1 -20 0 20 40 60 80 -40 -90 -45 0 -135 0.1 1m mag phase figure 5. ccv loop response c ci r ogmi cci gmi csi ictl gm out csip rs2 csin figure 6. cci loop diagram
MAX8730 low-cost battery charger ______________________________________________________________________________________ 23 ccs loop compensation the simplified schematic in figure 8 is sufficient to describe the operation of the MAX8730 when the input current-limit loop (ccs) is in control. since the output capacitor? impedance has little effect on the response of the input current-limit loop, only a single pole is required to compensate this loop. a css is the internal gain of the current-sense amplifier, rs1 = 10m ? in the typical application circuits. r ogms is the equivalent output impedance of the gms amplifier, which is greater than 10m ? . gms is the charge-current amplifier transconductance = 1?/mv. gm in is the dc-dc con- verter? input-referred transconductance = gm out /d = 2.22a/v/d. the loop-transfer function is given by: the loop-transfer function simplifies to: the crossover frequency is given by: for stability, choose a crossover frequency lower than 1/10 of the switching frequency: values for ccs greater than 10 times the minimum value may slow down the current-loop response exces- sively. figure 9 shows the bode plot of the input cur- rent-limit-loop frequency response using the values calculated above. cx gms f x v v cs osc in max batt min _ _ = 5 2 f gms c x v v co cs cs in max batt min _ _ _ = 2 ltf gms r sr c xrs rs ogms ogms cs / = + 1 12 since gm ars in css = 1 2 ltf gm a rsi gms r sr c in css ogms ogms cs = + 1 frequency (hz) magnitude (db) 100k 1k 10 -20 0 20 40 60 100 80 -40 -45 0 -90 0.1 mag phase figure 7. cci loop response c cs r ogms gms css cls ccs cssp rs1 cssi gm in system load adapter input figure 8. cci loop diagram frequency (hz) magnitude (db) 100k 10m 1k 10 -20 0 20 40 60 100 80 -40 -45 0 -90 0.1 mag phase phase (degrees) figure 9. ccs loop response
MAX8730 low-cost battery charger 24 ______________________________________________________________________________________ mosfet drivers the dhi output is optimized for driving moderate-sized power mosfets. this is consistent with the variable duty factor that occurs in the notebook computer envi- ronment where the battery voltage changes over a wide range. dhi swings from src to dhiv and has a typical impedance of 1 ? sourcing and 4 ? sinking. design procedure mosfet selection choose the p-channel mosfets according to the max- imum required charge current. the mosfet (p4) must be able to dissipate the resistive losses plus the switch- ing losses at both v src(min) and v src(max) . the worst-case resistive power losses occur at the maximum battery voltage. calculate the resistive losses according to the following equation: calculate the switching losses according to the follow- ing equation: where c rss is the reverse transfer capacitance of the mosfet, and i gate is the peak gate-drive source/sink current. these calculations provide an estimate and are not a substitute for breadboard evaluation, preferably includ- ing a verification using a thermocoupler mounted on the mosfet. generally, a small mosfet is desired to reduce switch- ing losses at v batt = v src / 2. this requires a tradeoff between gate charge and resistance. switching losses in the mosfet can become significant when the maxi- mum ac adapter voltage is applied. if the mosfet that was chosen for adequate r ds(on) at low supply volt- ages becomes hot when subjected to v src(max) , then choose a mosfet with lower gate charge. the actual switching losses that can vary due to factors include the internal gate resistance, threshold voltage, source inductance, and pc board layout characteristics. see table 3 for suggestions about mosfet selection. schottky selection the schottky diode conducts the inductor current dur- ing the off-time. choose a schottky diode with the appropriate thermal resistance to guarantee that it does not overheat: ja j max a max f chg batt min src max tt vxi x v v __ _ _ < ? ? ? ? ? ? ? ? 1 pd x xq i xv i v c f switching g gate src max x chg src max x rss () () = ? ? ? ? ? ? + () 1 2 2 2 pd v v xi r sis ce batt src chg ds on re tan () = 2 table 3. recommended mosfets max charge current (a) mosfet pin-package q g ( nc) r dson (m ? ) r ja (?w) t max (c) 3 si3457dv 6-sot23 8 75 78 +150 2.5 fdc658p 6-sot23 12 75 78 +150 3.5 fds9435a 8-so 14 80 50 +175 3.5 nds9435a 8-so 14 80 50 +175 4 fds4435 8-so 24 35 50 +175 4 fds6685 8-so 24 35 50 +175 4.5 fds6675a 8-so 34 19 50 +175
MAX8730 low-cost battery charger ______________________________________________________________________________________ 25 where ja is the thermal resistance of the package (in ?/w), t j_max is the maximum junction temperature of the diode, t a_max is the maximum ambient tempera- ture of the system, and v f is the forward voltage of the schottky diode. the schottky size and cost can be reduced by utilizing the MAX8730 foldback function. see the foldback current section for more information. select the schottky diode to minimize the battery leakage current when the charger is shut down. inductor selection the MAX8730 uses a fixed inductor current ripple architecture to minimize the inductance. the charge current, ripple, and operating frequency (off-time) affects inductor selection. for a good trade-off of inductor size and efficiency, choose the inductance according to the following equation: where k off is the off-time constant (5.6v x ? typically). higher inductance values decrease the rms current at the cost of inductor size. inductor l1 must have a saturation current rating of at least the maximum charge current plus 1/2 of the ripple current ( ? i l ): i sat = i chg + (1/2) ? i l the ripple current is determined by: the ripple current is only dependent on inductance value and is independent of input and output voltage. see the ripple current vs. v batt graph in the typical operating characteristics . see table 4 for suggestions about inductor selection. input capacitor selection the input capacitor must meet the ripple current requirement (i rms ) imposed by the switching currents. ceramic capacitors are preferred due to their resilience to power-up surge currents: at 50% duty cycle. the input capacitors should be sized so that the tem- perature rise due to ripple current in continuous con- duction does not exceed about 10?. the maximum ripple current occurs at 50% duty factor or v src = 2 x v batt , which equates to 0.5 x i chg . if the application of interest does not achieve the maximum value, size the input capacitors according to the worst-case condi- tions. see table 5 for suggestions about input capaci- tor selection. ii vv v v i rms chg batt src batt src chg = ? () ? ? ? ? ? ? ? ? = 2 ? i k l l off = l k xi off chg . = 04 table 4. recommended inductors application (a) inductor size (mm) l (?) i sat (a) r l (m ? ? ? ? ) 2.5 cdrh6d38 8.3 x 8.3 x 3 3.3 3.5 20 2.5 cdrh8d28 7 x 7 x 4 4.7 3.4 24.7 3.5 cdrh8d38 8.3 x 8.3 x 4 3.5 4.4 24 table 5. recommended input capacitors application (a) input capacitor capacitance( ?) volts (v) rms at 10? (a) < 3 gmk316f47s2g 4.7 35 1.8 < 4 gmk325f106zh 4.7 35 2.4 < 4 tmk325bj475mn 10 25 2.5
MAX8730 low-cost battery charger 26 ______________________________________________________________________________________ output capacitor selection the output capacitor absorbs the inductor ripple cur- rent and must tolerate the surge current delivered from the battery when it is initially plugged into the charger. as such, both capacitance and esr are important parameters in specifying the output capacitor as a filter and to ensure stability of the dc-dc converter (see the compensation section). beyond the stability require- ments, it is often sufficient to make sure that the output capacitor? esr is much lower than the battery? esr. either tantalum or ceramic capacitors can be used on the output. ceramic devices are preferable because of their good voltage ratings and resilience to surge cur- rents. for a ceramic output capacitor, select the capac- itance according to the following equation: the output ripple requirement of a charger is typically only constrained by the overvoltage protection circuitry of the battery protector and the overvoltage protection of the charger. for proper operation, ensure that the ripple is smaller than the overvoltage protection thresh- old of both the charger and the battery protector. if the protector? overvoltage protection is filtered, the battery protector may not be a constraint. applications information adapter soft-start the adapter selection mosfets may be soft-started to reduce adapter surge current upon adapter selection. figure 10 shows the adapter soft-start application using miller capacitance for optimum soft-start timing and power dissipation. system short-circuit iinp configuration the MAX8730 has a system short-circuit protection fea- ture. when v iinp is greater than 4.2v, the MAX8730 latches off pds. pds remains off until the adapter is removed and reinserted. for fast response to system overcurrent, add an rc (c13 and r15), as shown in figure 11. select r15 according to the following equation: where: v sst = 4.2v. i sst = short-circuit system current threshold. since sys- tem short-circuit triggers a latch, it is important to choose i sst high enough to prevent unintentional triggers. select c13 according to the following equation: c t r delay 13 15 = r v gxrs xi x r sst iinp sst 15 107 10 =? . c k xlxv x vv v out off ripple src batt batt > ? + ? ? ? ? ? ? 2 8 11 adapter system load c ss2 10nf r ss2 6k ? r ss1 18k ? c ss1 32nf pds src figure 10. adapter soft-start modification r10 c6 r15 MAX8730 c13 iinp figure 11. system short-circuit iinp configuration
MAX8730 low-cost battery charger ______________________________________________________________________________________ 27 for typical applications, choose t delay = 20? (depends on the p-mosfet selected for the pds switch). the following components can be used for a 10a sys- tem short-current design: r10 = 8.66k ? c6 = 0.1? r15 = 7.15k ? c13 = 2.7nf foldback current at low duty cycles, most of the charge current is con- ducted through the schottky diode (d1). to reduce the requirements of the schottky diode, the MAX8730 has a foldback charge current feature. when the battery volt- age falls below 5 x v relth , ictl sinks 6a. add a series resistor to ictl to adjust the charge current fold- back, as shown in figure 12: layout and bypassing bypass src, asns, ldo, dhiv, and ref as shown in figure 1. good pc board layout is required to achieve specified noise immunity, efficiency, and stable performance. the pc board layout artist must be given explicit instructions?referably, a sketch showing the place- ment of the power-switching components and high- current routing. refer to the pc board layout in the MAX8730 evaluation kit for examples. use the following step-by-step guide: 1) place the high-power connections first, with their grounds adjacent: ? minimize the current-sense resistor trace lengths, and ensure accurate current sensing with kelvin connections. ? minimize ground trace lengths in the high-current paths. ? minimize other trace lengths in the high-current paths. ? use > 5mm wide traces in the high-current paths. ? connect to the input capacitors directly to the source of the high-side mosfet (10mm max length). place the input capacitor between the input current-sense resistor and the source of the high-side mosfet. 2) place the ic and signal components. quiet connec- tions to ref, ccv, cci, ccs, acin, swref, and ldo src should be returned to a separate ground (gnd) island. there is very little current flowing in these traces, so the ground island need not be very large. when placed on an inner layer, a sizable ground island can help simplify the layout because the low current connections can be made through vias. the ground pad on the backside of the pack- age should be the star connection to this quiet ground island. 3) keep the gate drive trace (dhi) and src path as short as possible (l < 20mm), and route them away from the current-sense lines and ref. bypass dhiv directly to the source of the high-side mosfet. these traces should also be relatively wide (w > 1.25mm). 4) place ceramic bypass capacitors close to the ic. the bulk capacitors can be placed further away. r1 4 = 1 6 a r8 r7 + r8 xv ref ? i foldback xrs2x3.6v 135 mv ? ? ? ? ? ? ? ? ? r8 x r7 r7 + r8 ref r7 r8 r14 ictl figure 12. ictl foldback current adjustment
MAX8730 low-cost battery charger 28 ______________________________________________________________________________________ chip information transistor count: 3307 process: bicmos MAX8730 5mm x 5mm thin qfn top view 26 27 25 24 10 9 11 ldo ref cls acin vctl 12 asns csin gnd ccs csip ccv cci 12 cssn 4567 20 21 19 17 16 15 cssp pds ictl iinp mode swref batt 3 18 28 8 pdl + relth src 23 13 refon dhi 22 14 inpon dhiv * exposed paddle acok pin configuration
MAX8730 low-cost battery charger 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. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 29 2005 maxim integrated products printed usa is a registered trademark of maxim integrated products, inc. package 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 .) qfn thin.eps d2 (nd-1) x e e d c pin # 1 i.d. (ne-1) x e e/2 e 0.08 c 0.10 c a a1 a3 detail a e2/2 e2 0.10 m c a b pin # 1 i.d. b 0.35x45 d/2 d2/2 l c l c e e l c c l k l l detail b l l1 e aaaaa marking i 1 2 21-0140 package outline, 16, 20, 28, 32, 40l thin qfn, 5x5x0.8mm -drawing not to scale- l e/2 common dimensions max. exposed pad variations d2 nom. min. min. e2 nom. max. ne nd pkg. codes 1. dimensioning & tolerancing conform to asme y14.5m-1994. 2. all dimensions are in millimeters. angles are in degrees. 3. n is the total number of terminals. 4. the terminal #1 identifier and terminal numbering convention shall conform to jesd 95-1 spp-012. details of terminal #1 identifier are optional, but must be located within the zone indicated. the terminal #1 identifier may be either a mold or marked feature. 5. dimension b applies to metallized terminal and is measured between 0.25 mm and 0.30 mm from terminal tip. 6. nd and ne refer to the number of terminals on each d and e side respectively. 7. depopulation is possible in a symmetrical fashion. 8. coplanarity applies to the exposed heat sink slug as well as the terminals. 9. drawing conforms to jedec mo220, except exposed pad dimension for t2855-3 and t2855-6. notes: symbol pkg. n l1 e e d b a3 a a1 k 10. warpage shall not exceed 0.10 mm. jedec 0.70 0.80 0.75 4.90 4.90 0.25 0.25 0 -- 4 whhb 4 16 0.35 0.30 5.10 5.10 5.00 0.80 bsc. 5.00 0.05 0.20 ref. 0.02 min. max. nom. 16l 5x5 l 0.30 0.50 0.40 -- - -- - whhc 20 5 5 5.00 5.00 0.30 0.55 0.65 bsc. 0.45 0.25 4.90 4.90 0.25 0.65 - - 5.10 5.10 0.35 20l 5x5 0.20 ref. 0.75 0.02 nom. 0 0.70 min. 0.05 0.80 max. -- - whhd-1 28 7 7 5.00 5.00 0.25 0.55 0.50 bsc. 0.45 0.25 4.90 4.90 0.20 0.65 - - 5.10 5.10 0.30 28l 5x5 0.20 ref. 0.75 0.02 nom. 0 0.70 min. 0.05 0.80 max. -- - whhd-2 32 8 8 5.00 5.00 0.40 0.50 bsc. 0.30 0.25 4.90 4.90 0.50 - - 5.10 5.10 32l 5x5 0.20 ref. 0.75 0.02 nom. 0 0.70 min. 0.05 0.80 max. 0.20 0.25 0.30 down bonds allowed yes 3.10 3.00 3.20 3.10 3.00 3.20 t2055-3 3.10 3.00 3.20 3.10 3.00 3.20 t2055-4 t2855-3 3.15 3.25 3.35 3.15 3.25 3.35 t2855-6 3.15 3.25 3.35 3.15 3.25 3.35 t2855-4 2.60 2.70 2.80 2.60 2.70 2.80 t2855-5 2.60 2.70 2.80 2.60 2.70 2.80 t2855-7 2.60 2.70 2.80 2.60 2.70 2.80 3.20 3.00 3.10 t3255-3 3 3.20 3.00 3.10 3.20 3.00 3.10 t3255-4 3 3.20 3.00 3.10 no no no no yes yes yes yes 3.20 3.00 t1655-3 3.10 3.00 3.10 3.20 no no 3.20 3.10 3.00 3.10 t1655n-1 3.00 3.20 3.35 3.15 t2055-5 3.25 3.15 3.25 3.35 yes 3.35 3.15 t2855n-1 3.25 3.15 3.25 3.35 no 3.35 3.15 t2855-8 3.25 3.15 3.25 3.35 yes 3.20 3.10 t3255n-1 3.00 no 3.20 3.10 3.00 l 0.40 0.40 ** ** ** ** ** ** ** ** ** ** ** ** ** ** see common dimensions table 0.15 11. marking is for package orientation reference only. i 2 2 21-0140 package outline, 16, 20, 28, 32, 40l thin qfn, 5x5x0.8mm -drawing not to scale- 12. number of leads shown are for reference only. 3.30 t4055-1 3.20 3.40 3.20 3.30 3.40 ** yes 0.05 0 0.02 0.60 0.40 0.50 10 ----- 0.30 40 10 0.40 0.50 5.10 4.90 5.00 0.25 0.35 0.45 0.40 bsc. 0.15 4.90 0.25 0.20 5.00 5.10 0.20 ref. 0.70 min. 0.75 0.80 nom. 40l 5x5 max. 13. lead centerlines to be at true position as defined by basic dimension "e", 0.05. t1655-2 ** yes 3.20 3.10 3.00 3.10 3.00 3.20 t3255-5 yes 3.00 3.10 3.00 3.20 3.20 3.10 ** exceptions

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