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general description the max8903a/max8903c/max8903d are integrated 1-cell li+ chargers and smart power selectors with dual (ac adapter and usb) power inputs. the switch mode charger uses a high switching frequency to elimi- nate heat and allow tiny external components. it can operate with either separate inputs for usb and ac adapter power, or from a single input that accepts both. all power switches for charging and switching the load between battery and external power are included on- chip. no external mosfets, blocking diodes, or cur- rent-sense resistors are required. the max8903a/max8903c/max8903d feature opti- mized smart power control to make the best use of limit- ed usb or adapter power. battery charge current and sys output current limit are independently set. power not used by the system charges the battery. charge current and sys output current limit can be set up to 2a while usb input current can be set to 100ma or 500ma. automatic input selection switches the system from bat- tery to external power. the dc input operates from 4.15v to 16v with up to 20v protection, while the usb input has a range of 4.1v to 6.3v with up to 8v protection. the max8903a/max8903c/max8903d internally block current from the battery and system back to the dc and usb inputs when no input supply is present. other fea- tures include pre-qual charging and timer, fast charge timer, overvoltage protection, charge status and fault outputs, power-ok monitors, and a battery thermistor monitor. in addition, on-chip thermal limiting reduces battery charge rate and ac adapter current to prevent charger overheat ing. the max8903a/max8903c/ max8903d are available in a 4mm x 4mm, 28-pin thin qfn package. applications features efficient dc-dc converter eliminates heat 4mhz switching for tiny external components instant on?orks with no battery or low battery dual current-limiting input circuits?c adapter or usb automatic adapter/usb/battery switchover to support load transients 50m system-to-battery switch supports usb spec thermistor monitor integrated current-sense resistor no external mosfets or diodes 4.1v to 16v input operating voltage range max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power ________________________________________________________________ maxim integrated products 1 19-4410; rev 2; 11/09 for pricing, delivery, and ordering information, please contact maxim direct at 1-888-629-4642, or visit maxim? website at www.maxim-ic.com. evaluation kit available pin configuration appears at end of data sheet. charge and sys load switch dc sys bat ac adapter or usb system load battery gnd usb usb charge current load current lx cs pwm step-down max8903a max8903c max8903d typical operating circuit smart power selector is a trademark of maxim integrated products, inc. selector guide part minimum sys voltage (v) battery regulation voltage (v) max8903aeti+ 3.0 4.2 MAX8903CETI+ 3.4 4.2 max8903deti+ 3.4 4.1 pdas, palmtops, and wireless handhelds personal navigation devices smart cell phones portable multimedia players mobile internet devices ultra mobile pcs ordering information + denotes a lead(pb)-free/rohs-compliant package. * ep = exposed pad. part temp range pin-package max8903aeti+ -40? to +85? 28 thin qfn-ep* MAX8903CETI+ -40? to +85? 28 thin qfn-ep* max8903deti+ -40? to +85? 28 thin qfn-ep*
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 2 _______________________________________________________________________________________ electrical characteristics (v dc = v usb = 5v, v bat = 4v, circuit of figure 2, t a = -40c to +85c, unless otherwise noted. typical values are at t a = +25c.) (note 1) stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. these are stress ratings only, and functional operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. exposure to absolute maximum rating conditions for extended periods may affect device reliability. parameter conditions min typ max units dc input dc operating range 4.15 16 v no valid usb input 3.9 4.0 4.1 dc undervoltage threshold when v dok goes low, v dc rising, 500mv typical hysteresis valid usb input 4.0 4.3 4.4 v dc overvoltage threshold when v dok goes high, v dc rising, 500mv typical hysteresis 16.5 17 17.5 v charger enabled, no switching, v sys = 5v 2.3 4 charger enabled, f = 3mhz, v dc = 5v 15 c har g er enab l ed , v c e n = 0v , 100m a u s b m od e ( n ote 2) 1 2 c har g er enab l ed , v c e n = 5v , 100m a u s b m od e ( n ote 2) 1 2 dc supply current v dcm = 0v, v usus = 5v 0.10 0.25 ma dc high-side resistance 0.15 ? dc low-side resistance 0.15 ? dc-to-bat dropout resistance 0.31 ? dc-to-bat dropout voltage when sys regulation and charging stops, v dc falling, 200mv hysteresis 01530mv v dc = 8v, v bat = 4v 4 switching frequency v dc = 5v, v bat = 3v 3 mhz dc step-down output current- limit step range 0.5 2 a r idc = 3k? 1900 2000 2100 r idc = 6k? 950 1000 1050 dc step-down output current limit v dc = 6v, v sys = 4v r idc = 12k? 450 500 550 ma no valid usb input 1 ms dc soft-start time valid usb input before soft-start 20 s absolute maximum ratings dc, lx to gnd .......................................................-0.3v to +20v dcm to gnd ..............................................-0.3v to (v dc + 0.3v) dc to sys .................................................................-6v to +20v bst to gnd ...........................................................-0.3v to +26v bst to lx ................................................................-0.3v to +6v usb to gnd .............................................................-0.3v to +9v usb to sys..................................................................-6v to +9v vl to gnd ................................................................-0.3v to +6v thm, idc, iset, ct to gnd .........................-0.3v to (vl + 0.3v) dok, flt, cen, uok, chg, usus, bat, sys, iusb, cs to gnd ................................-0.3v to +6v sys to bat ...............................................................-0.3v to +6v pg, ep (exposed pad) to gnd .............................-0.3v to +0.3v dc continuous current (total in two pins)......................2.4a rms usb continuous current.......................................................1.6a lx continuous current (total in two pins).......................2.4a rms cs continuous current (total in two pins) ......................2.4a rms sys continuous current (total in two pins) .......................3a rms bat continuous current (total in two pins) .......................3a rms vl short circuit to gnd .............................................continuous continuous power dissipation (t a = +70c) 28-pin thin qfn-ep multilayer (derate 28.6mw/c above +70c) ..........2286mw 28-pin thin qfn-ep single-layer (derate 20.8mw/c above +70c)...1666.7mw operating temperature range ...........................-40c to +85c junction temperature range ............................-40c to +150c storage temperature range .............................-65c to +150c soldering temperature (reflow) .......................................+260c
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power _______________________________________________________________________________________ 3 parameter conditions min typ max units dc output current 500ma usb mode (note 3) v dcm = 0v, v iusb = 5v 450 475 500 ma dc output current 100ma usb mode (note 2) v dcm = 0v, v iusb = 0v 90 95 100 ma sys to dc reverse current blocking v sys = 5.5v, v dc = 0v 0.01 a usb input usb operating range 4.1 6.3 v usb standoff voltage 8v usb undervoltage threshold when v uok goes low, v usb rising, 500mv hysteresis 3.95 4.0 4.05 v usb overvoltage threshold when v uok goes high, v usb rising, 500mv hysteresis 6.8 6.9 7.0 v v iusb = 0v (100ma setting) 90 95 100 usb current limit v iusb = 5v (500ma setting) 450 475 500 ma i sys = i bat = 0ma, v cen = 0v 1.3 3 i sys = i bat = 0ma, v cen = 5v 0.8 2 usb supply current v usus = 5v (usb suspend mode) 0.115 0.25 ma minimum usb to bat headroom 0 15 30 mv usb to sys dropout resistance 0.2 0.35 ? v usb rising 1 ms usb soft-start time v dc falling below dc uvlo to initiate usb soft-start 20 s sys output max8903a 3.0 minimum sys regulation voltage (v sysmin ) i sys = 1a, v bat < v sysmin max8903c/max8903d 3.4 v regulation voltage i sys = 0a 4.3 4.4 4.5 v load regulation i sys = 0 to 2a 40 mv/a cs to sys resistance v dc = 6v, v dcm = 5v, v sys = 4v, i cs = 1a 0.07 ? sys to cs leakage v sys = 5.5v, v dc = v cs = 0v 0.01 a bat to sys resistance v dc = v usb = 0v, v bat = 4.2v, i sys = 1a 0.05 0.1 ? bat to sys reverse regulation voltage v usb = 5v, v dc = 0v, v iusb = 0v, i sys = 200ma 50 75 100 mv sys undervoltage threshold sys falling, 200mv hysteresis (note 4) 1.8 1.9 2.0 v battery charger t a = +25c 4.179 4.2 4.221 max8930a/ max8903c t a = -40c to +85c 4.158 4.2 4.242 t a = +25c 4.079 4.1 4.121 bat regulation voltage (v batreg )i bat = 0ma max8903d t a = -40c to +85c 4.059 4.1 4.141 v c har g er restar t thr eshol d ( v rs tr t ) change in v bat from done to fast-charge -150 -100 -60 mv bat prequal threshold v bat rising, 180mv hysteresis 2.9 3 3.1 v prequal charge current percentage of fast-charge current set at iset 10 % electrical characteristics (continued) (v dc = v usb = 5v, v bat = 4v, circuit of figure 2, t a = -40c to +85c, unless otherwise noted. typical values are at t a = +25c.) (note 1)
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 4 _______________________________________________________________________________________ parameter conditions min typ max units r iset = 600? 1800 2000 2200 r iset = 1.2k? 900 1000 1100 fast-charge current r iset = 2.4k? 450 500 550 ma done threshold percentage of fast-charge, i bat decreasing 10 % r iset resistor range 0.6 2.4 k ? iset output voltage 1.5 v iset current monitor gain 1.25 ma/a no dc or usb input 0.05 4 bat leakage current with valid input power, v cen = 5v 1 6 a charger soft-start time 1.0 ms charger thermal limit temperature 100 c charger thermal limit gain charge current = 0 at + 120c 5 %/c charger timer prequalification time c ct = 0.15f 33 min fast-charge time c ct = 0.15f 660 min timer accuracy -15 +15 % timer extend current threshold percentage of fast-charge current below which the timer clock operates at half-speed 40 50 60 % timer suspend current threshold percentage of fast-charge current below which timer clock pauses 16 20 24 % charge done delay time from done threshold detection until charger turns off and chg goes high 15 s thermistor monitor thm threshold, hot when charging is suspended, 1% hysteresis 0.27 x v vl 0.28 x v vl 0.29 x v vl v thm threshold, cold when charging is suspended, 1% hysteresis 0.73 x v vl 0.74 x v vl 0.75 x v vl v thm threshold, disabled thm function is disabled below this voltage 0.0254 x v vl 0.03 x v vl 0.036 x v vl v thm = gnd or vl; t a = +25c -0.1 +0.001 +0.2 thm input leakage thm = gnd or vl; t a = +85c 0.01 a thermal shutdown, vl, and logic i/o: chg, flt, dok, uok, dcm, cen, usus, iusb high level 1.3 low level 0.4 v logic-input thresholds (dcm, cen , usus, iusb) hysteresis 50 mv t a = +25c 0.001 1 logic-input leakage current ( cen , usus, iusb) v input = 0 to 5.5v t a = +85c 0.01 a t a = +25c 0.001 1 logic-input leakage current (dcm) v dcm = 0 to 16v v dc = 16v t a = +85c 0.01 a electrical characteristics (continued) (v dc = v usb = 5v, v bat = 4v, circuit of figure 2, t a = -40c to +85c, unless otherwise noted. typical values are at t a = +25c.) (note 1)
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power _______________________________________________________________________________________ 5 parameter conditions min typ max units sinking 1ma 8 50 logic output voltage, low ( chg , flt, dok , uok ) sinking 10ma 80 mv t a = +25c 0.001 1 open-drain output leakage c ur rent, hi g h ( chg , flt , dok , uok ) v out = 5.5v t a = +85c 0.01 a vl output voltage v dc = v usb = 6v, i vl = 0 to 1ma 4.6 5 5.4 v vl uvlo threshold v vl falling; 200mv hysteresis 3.2 v thermal shutdown temperature 160 c thermal shutdown hysteresis 15 c electrical characteristics (continued) (v dc = v usb = 5v, v bat = 4v, circuit of figure 2, t a = -40c to +85c, unless otherwise noted. typical values are at t a = +25c.) (note 1) note 1: limits are 100% production tested at t a = +25c. limits over the operating temperature range are guaranteed by design. note 2: for the 100ma usb mode using the dc input, the step-down regulator is turned off and its high-side switch operates as a linear regulator with a 100ma current limit. the linear regulators output is connected to lx and its output current flows through the inductor into cs and finally to sys. note 3: for the 500ma usb mode, the actual current drawn from usb is less than the output current due to the input/output current ratio of the dc-dc converter. note 4: for short-circuit protection, sys sources 25ma below v sys = 400mv, and 50ma for v sys between 400mv and 2v. typical operating characteristics (t a = +25c, unless otherwise noted.) battery charger efficiency vs. battery voltage max8903a toc01 battery voltage (v) efficiency (%) 4.5 4.0 3.0 3.5 2.0 2.5 1.5 10 20 30 40 50 60 70 80 90 100 0 1.0 5.0 v dc = 8v i bat = 0.15a i bat = 1.5a v dc = 5v v dc = 12v 0.0 0.5 1.0 1.5 2.0 2.5 3.0 4.0 3.5 4.5 48 6 10121416 switching frequency vs. v dc max8903a toc02 dc voltage (v) switching frequency (mhz) v bat = 3v r iset = 1.2k ? v cen = 0v v bat = 4v sys efficiency vs. dc voltage max8903a toc03 sys output current (ma) sys efficiency (%) 1000 100 10 10 20 30 40 50 60 70 80 90 100 0 1 10000 v cen = 1v v sys = 4.4v v dc = 4.5v v dc = 6v v dc = 11v v dc = 16v
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 6 _______________________________________________________________________________________ typical operating characteristics (continued) (t a = +25c, unless otherwise noted.) 0.0 0.5 1.0 1.5 2.0 2.5 3.0 4.0 3.5 4.5 48 6 10121416 switching frequency vs. v dc max8903a toc02 dc voltage (v) switching frequency (mhz) v bat = 3v r iset = 1.2k ? v cen = 0 v bat = 4v 0 40 20 80 60 120 100 140 023 1 4567 usb quiescent current vs. usb voltage max8903a toc05 usb voltage (v) usb quiescent current ( a) usb suspend 0 20 10 40 30 70 60 50 80 04 5 6 321 battery leakage current vs. battery voltage max8903a toc06 battery voltage (v) battery leakage current (na) usb unconnected 0 20 10 40 30 70 80 60 50 90 -40 35 60 -15 10 85 battery leakage current vs. ambient temperature max8903a toc07 temperature ( c) battery leakage current (na) charge current vs. battery voltage?usb max8903a toc08 battery voltage (v) charge current (ma) 4.0 3.5 3.0 2.5 2.0 50 100 150 200 250 300 350 400 450 500 0 1.5 4.5 charge enabled i bat set to 1.5a max8903d v bat rising v iusb = v usb v iusb = 0 charge current vs. battery voltage?dc mode max8903a toc09 battery voltage (v) charge current (ma) 4.0 3.5 3.0 2.5 2.0 200 400 600 800 1000 1200 0 1.5 4.5 charger enabled i bat set to 1a i dc set to 2a max8903a v bat rising normalized charge current vs. ambient temperature max8903a toc10 temperature (c) normalized charge current 603510-15 0.990 0.995 1.000 1.005 1.010 1.015 0.985 -40 85 v usb = 5v, v bat = 4v max8903a/c battery regulation voltage vs. ambient temperature max8903a toc11 temperature ( c) normalized battery regulation voltage (%) 60 35 10 -15 99.6 99.7 99.8 99.9 100.0 100.1 100.2 100.3 100.4 100.5 99.5 -40 85 0 1.5 1.0 0.5 2.5 2.0 4.5 4.0 3.5 3.0 5.0 01234567 sys voltage vs. usb voltage max8903a toc12 usb voltage (v) sys voltage (v) v usb falling v cen = 5v v bat = 0v v dc = 0v v usb rising r sys = 1m?
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power _______________________________________________________________________________________ 7 typical operating characteristics (continued) (t a = +25c, unless otherwise noted.) 0 1.0 0.5 2.0 1.5 3.0 2.5 3.5 4.5 4.0 5.0 0 468 2 1012141618 sys voltage vs. dc voltage max8903a toc13 dc voltage (v) sys voltage (v) v dc rising v dc falling v cen = 5v v bat = 0v v dc = 0v 3.80 3.90 4.10 4.00 4.30 4.40 4.20 4.50 0 0.3 0.5 0.1 0.7 0.9 1.1 1.3 1.5 sys voltage vs. sys output current, dc input max8903a toc14 sys output current (a) sys voltage (v) v dc = 5.75v usb and dc unconnected v bat = 4v 4.355 4.365 4.360 4.375 4.370 4.380 4.385 4.395 4.390 4.400 0 100 50 200150 300250 400350 500450 sys voltage vs. sys output current, usb input max8903a toc15 sys output current (ma) sys voltage (v) v usb = 5v 0 1 2 3 4 5 6 04 2 6 8 1012141618 vl voltage vs. dc voltage max8903a toc16 dc voltage (v) vl voltage (v) max8903a/max8903c charge profile?1400mah battery adapter input?1a charge max8903a toc17 time (min) v bat (v) i bat (a) 120100 60 80 4020 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 5.5 6.0 0 0.2 0.4 0.6 0.8 1.0 1.2 0.0 0 140 v bat i dc set to 1a i bat set to 2a i bat max8903a/max8903c charge profile?1400mah battery usb input?500ma charge time (min) v bat (v) i bat (a) 180160120 140 40 60 80 100 20 0.5 1.0 1.5 2.0 2.5 3.0 3.5 4.0 4.5 5.0 0 0.050 0.100 0.150 0.200 0.250 0.300 0.350 0.400 0.450 0.500 0 0 200 v bat i bat max8903a toc18 i usb set to 500ma i bat set to 2a 200ns/div dc switching waveforms?light load 20mv/div ac-coupled max8903a toc19 500ma/div 0a 5v/div 0v v out v lx i lx r sys = 44? dc switching waveforms?heavy load max8903a toc20 200ns/div v lx v out i lx 5v/div 0v 20mv/div ac-coupled 500ma/div 0a r sys = 5?
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 8 _______________________________________________________________________________________ typical operating characteristics (continued) (t a = +25c, unless otherwise noted.) 200s/div usb resume 5v/div max8903a toc28 500ma/div 2v/div 500ma/div 475ma -475ma 3v 0v 0a 3.6v 0a 3.6v 3.8v battery charger soft-start c usb charging v usus i usb v sys i bat 400s/div dc connect with no usb (r sys = 25?) 2v/div max8903a toc22 5v/div 1a/div 1a/div 3.6v 3.84v 3.6v 3.44v c dc charging c sys charging 850ma -1a battery charger soft-start 144ma 0a v sys v bat i dc i bat -i bat = charging 40s/div dc disconnect with no usb (r sys = 25?) 2v/div max8903a toc23 5v/div 1a/div 1a/div 3.6v 3.68v 850ma -1a 144ma 0a v sys v bat i dc i bat 3.6v -i bat = charging 100s/div sys load transient (0 to 1a) 50mv/div ac coupled max8903a toc24 500ma/div 0a v sys i sys 400s/div usb connect with no dc (r sys = 25?) 2v/div max8903a toc25 5v/div 500ma/div 500ma/div 3.6v c usb charging battery charger soft-start 144ma v sys v usb i usb i bat 3.5v 3.75v 5v 475ma -330ma 100s/div usb disconnect with no dc (r sys = 25?) 2v/div max8903a toc26 5v/div 500ma/div 500ma/div 3.6v 475ma v sys v usb i usb i bat 5v 144ma -330ma 200s/div usb suspend 5v/div max8903a toc27 500ma/div 2v/div 500ma/div 475ma -475ma v usus i usb v sys i bat 3v 0v 0a 3.7v 0a dc connect with usb connected (r sys = 25?) max8903a toc21 200s/div i dc v sys i usb i bat 2v/div 500ma/div 500ma/div 500ma/div 0a 3.6v 347ma -i bat = charging 475ma -335ma
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power _______________________________________________________________________________________ 9 pin description pin name function 1, 2 pg power ground for step-down low-side synchronous n-channel mosfet. both pg pins must be connected together externally. 3, 4 dc dc power input. dc is capable of delivering up to 2a to sys. dc supports both ac adapter and usb inputs. the dc current limit is set through dcm, iusb, or idc depending on the input source used. see table 2. both dc pins must be connected together externally. connect at least a 4.7f ceramic capacitor from dc to pg. 5 dcm current-limit mode setting for the dc power input. when logic-high, the dc input current limit is set by the resistance from idc to gnd. when logic-low, the dc input current limit is internally programmed to 500ma or 100ma, as set by the iusb logic input. there is an internal diode from dcm (anode) to dc (cathode) as shown in figure 1. 6 bst high-side mosfet driver supply. bypass bst to lx with a 0.1f ceramic capacitor. 7 iusb usb current-limit set input. drive iusb logic-low to set the usb current limit to 100ma. drive iusb logic- high to set the usb current limit to 500ma. 8 dok dc power-ok output. active-low open-drain output pulls low when a valid input is detected at dc. dok is still valid when the charger is disabled ( cen high). 9vl logic ldo output. vl is the output of an ldo that powers the max8903a/max8903c/max8903d internal circuitry and charges the bst capacitor. connect a 1f ceramic capacitor from vl to gnd. 10 ct charge timer set input. a capacitor (c ct ) from ct to gnd sets the fast-charge and prequal fault timers. connect to gnd to disable the timer. 11 idc dc current-limit set input. connect a resistor (r idc ) from idc to gnd to program the current limit of the step-down regulator from 0.5a to 2a when dcm is logic-high. 12 gnd ground. gnd is the low-noise ground connection for the internal circuitry. 13 iset charge current set input. a resistor (r iset ) from iset to gnd programs the fast-charge current up to 2a. the prequal charge current is 10% of the fast-charge current. 14 cen charger enable input. connect cen to gnd to enable battery charging when a valid source is connected at dc or usb. connect to vl, or drive high to disable battery charging. 15 usus usb suspend input. drive usus logic-high to enter usb suspend mode, lowering usb current to 115a, and internally shorting sys to bat. 16 thm thermistor input. connect a negative temperature coefficient (ntc) thermistor from thm to gnd. connect a resistor equal to the thermistor +25c resistance from thm to vl. charging is suspended when the thermistor is outside the hot and cold limits. connect thm to gnd to disable the thermistor temperature sensor. 17 usb usb power input. usb is capable of delivering 100ma or 500ma to sys as set by the iusb logic input. connect a 4.7f ceramic capacitor from usb to gnd. 18 flt fault output. active-low, open-drain output pulls low when the battery timer expires before prequal or fast-charge completes. 19 uok usb power-ok output. active-low, open-drain output pulls low when a valid input is detected at usb. uok is still valid when the charger is disabled ( cen high). 20, 21 bat battery connection. connect to a single-cell li+ battery. the battery charges from sys when a valid source is present at dc or usb. bat powers sys when neither dc nor usb power is present, or when the sys load exceeds the input current limit. both bat pins must be connected together externally.
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 10 ______________________________________________________________________________________ pin description (continued) pin name function 22 chg charger status output. active-low, open-drain output pulls low when the battery is in fast-charge or prequal. otherwise, chg is high impedance. 23, 24 sys system supply output. sys connects to bat through an internal 50m ? system load switch when dc or usb are invalid, or when the sys load is greater than the input current limit. when a valid voltage is present at dc or usb, sys is limited to 4.4v. when the system load (i sys ) exceeds the dc or usb current limit, sys is regulated to 50mv below bat, and both the powered input and the battery service sys. bypass sys to gnd with a 10f x5r or x7r ceramic capacitor. both sys pins must be connected together externally. 25, 26 cs 70m? current-sense input. connect the step-down inductor from lx to cs. when the step-down regulator is on, there is a 70m ? current-sense mosfet from cs to sys. when the step-down regulator is off, the internal cs mosfet turns off to block current from sys back to dc. 27, 28 lx inductor connection. connect the inductor between lx and cs. both lx pins must be connected together externally. ep exposed pad. connect the exposed pad to gnd. connecting the exposed pad does not remove the requirement for proper ground connections to the appropriate pins.
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power ______________________________________________________________________________________ 11 sys battery connector bat+ bat- + ntc t thm usb bat iset li+ battery charger and sys load switch ic thermal regulation charger current- voltage control usb uok dc dok dc power management pwm step-down regulator pwr ok usb power management current- limited voltage regulator set input limit pwr ok vl chg flt ct charge termination and monitor charge timer thermistor monitor (see figure 7) cen input and charger current-limit set logic dcm dc iusb usus idc 500ma 100ma usb limit dc limit ac adapter gnd dc mode usb suspend to system load lx cs bst set input limit pg ep max8903a max8903c max8903d figure 1. functional block diagram
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 12 ______________________________________________________________________________________ circuit description the max8903a/max8903c/max8903d is a dual input charger with a 16v input for a wide range of dc sources and usb inputs. the ic includes a high-volt- age (16v) input dc-dc step-down converter that reduces charger power dissipation while also supplying power to the system load. the step-down converter supplies up to 2a to the system, the battery, or a com- bination of both. a usb charge input can charge the battery and power the system from a usb power source. when powered from usb or the dc input, system load current peaks that exceed what can be supplied by the input are sup- plemented by the battery. the max8903a/max8903c/max8903d also manages load switching from the battery to and from an external power source with an on-chip 50m ? mosfet. this switch also helps support load peaks using battery power when the input source is overloaded. pg pg dc dc bst lx lx cs cs sys sys bat bat flt uok dok fault output usb pwr ok dc pwr ok to vl r pu 4 x 100k ? 18 19 8 24 23 21 20 1 2 3 4 6 27 28 25 26 17 usb iset idc r iset r idc dcm thm cen iusb gnd ntc 10k? usus 5 9 16 12 charge on off 100ma 500ma usb suspend 14 7 15 to system load chg 22 charge indicator c dc 4.7f ct c ct 0.15f adapter vbus gnd c bst 0.1f l1 1h 13 11 c usb 4.7f usb 10 r t 10k? to dc 1-cell li+ c bat 10f c vl 1f c sys 10f vl max8903a max8903c max8903d figure 2. typical application circuit using a separate dc and usb connector
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power ______________________________________________________________________________________ 13 as shown in figure 1, the ic includes a full-featured charger with thermistor monitor, fault timer, charger status, and fault outputs. also included are power-ok signals for both usb and dc. flexibility is maintained with adjustable charge current, input current limit, and a minimum system voltage (when charging is scaled back to hold the system voltage up). the max8903a/max8903c/max8903d prevent over- heating during high ambient temperatures by limiting charging current when the die temperature exceeds +100c. dc input?ast hysteretic step-down regulator if a valid dc input is present, the usb power path is turned off and power for sys and battery charging is supplied by the high-frequency step-down regulator from dc. if the battery voltage is above the minimum system voltage (v sysmin , figure 4), the battery charger connects the system voltage to the battery for lowest power dissipation. the step-down regulation point is then controlled by three feedback signals: maximum step-down output current programmed at idc, maximum charger current programmed at iset, and maximum pg pg dc dc bst lx lx cs cs sys sys bat bat flt uok dok fault output usb pwr ok dc pwr ok to vl r pu 4 x 100k ? 18 19 8 24 23 21 20 1 2 3 4 6 27 28 25 26 17 usb iset idc r iset r idc dcm thm cen iusb gnd ntc 10k? usus 5 9 16 12 charge on off adapter usb 100ma 500ma usb suspend 14 7 15 to system load chg 22 charge indicator c dc 4.7f 499k? ct c ct 0.15f l1 1h c bst 0.1f 13 11 10 r t 10k? dc mode 1-cell li+ c bat 10f c sys 10f vl max8903a max8903c max8903d vbus 5-pin usb connector d- d+ id gnd c vl 1f figure 3. typical application circuit using a mini 5 style connector or other dc/usb common connector
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 14 ______________________________________________________________________________________ die temperature. the feedback signal requiring the smallest current controls the average output current in the inductor. this scheme minimizes total power dissi- pation for battery charging and allows the battery to absorb any load transients with minimum system volt- age disturbance. if the battery voltage is below v sysmin , the charger does not directly connect the system voltage to the bat- tery and the system voltage (v sys ) is slightly above v sysmin as shown in figure 4. the battery charger independently controls the battery charging current. v sysmin is set to 3.0v in the max8903a and 3.4v for max8903c/max8903d. after the battery charges to 50mv above v sysmin , the system voltage is connected to the battery. the battery fast-charge current then controls the step-down con- verter to set the average inductor current so that both the programmed input current limit and fast-charge cur- rent limit are satisfied. dc-dc step-down control scheme a proprietary hysteretic current pwm control scheme ensures fast switching and physically tiny external com- ponents. the feedback control signal that requires the smallest input current controls the center of the peak and valley currents in the inductor. the ripple current is internally set to provide 4mhz operation. when the input voltage decreases near the output voltage, very high duty cycle occurs and, due to minimum off-time, 4mhz operation is not achievable. the controller then provides minimum off-time, peak current regulation. similarly, when the input voltage is too high to allow 4mhz operation due to the minimum on-time, the con- troller becomes a minimum on-time, valley current regu- lator. in this way, ripple current in the inductor is always as small as possible to reduce ripple voltage on sys for a given capacitance. the ripple current is made to vary with input voltage and output voltage in a way that reduces frequency variation. however, the frequency still varies somewhat with operating conditions. see the typical operating characteristics . dc mode (dcm) as shown in table 2, the dc input supports both ac adapters (up to 2a) and usb (up to 500ma). with the dcm logic input set high, the dc input is in adapter mode and the dc input current limit is set by the resis- tance from idc to gnd (r idc ). calculate r idc accord- ing to the following equation: r idc = 6000v/i dc-max with the dcm logic input set low, the dc input current limit is internally programmed to 500ma or 100ma as set by the iusb logic input. with the iusb logic input set high, the dc input current limit is 500ma and the dc input delivers current to sys through the step-down regulator. with the iusb logic input set low, the dc input current limit is 100ma. in this 100ma mode, the step-down regulator is turned off and its high-side switch operates as a linear regulator with a 100ma cur- rent limit. the linear regulators output is connected to lx and its output current flows through the inductor into cs and finally to sys. the dcm pin has an internal diode to dc as shown in figure 1. to prevent current from flowing from dcm through the internal diode and to the dc input, dcm cannot be driven to a voltage higher than dc. the component (figures 2 and 3) function part c dc , c usb input filter capacitor 4.7f ceramic capacitor c vl vl filter capacitor 1.0f ceramic capacitor c sys sys output bypass capacitor 10f ceramic capacitor c bat battery bypass capacitor 10f ceramic capacitor c ct charger timing capacitor 0.15f low tc ceramic capacitor r pu (x4) logic output pullup resistors 100k ? thm negative tc thermistor philips ntc thermistor, p/n 2322-640-63103, 0k ? 5% at +25c r t thm pullup resistor 10k? r idc dc input current-limit programming resistor 3k ? 1%, for 2a limit r iset fast-charge current programming resistor 1.2k ? 1%, for 1a charging l1 dc input step-down inductor 1h inductor with i sat > 2a table 1. external components list for figures 2 and 3
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power ______________________________________________________________________________________ 15 circuit of figure 3 shows a simple mosfet and resistor on dcm to prevent any current from flowing from dcm through the internal diode to dc. this circuit of figure 3 allows a microprocessor to drive the gate of the mos- fet to any state at any time. an alternative to the simple mosfet and resistor on dcm as shown in figure 3 is to place a 1m ? resistor in series with the dcm input to the microprocessor. the microprocessor can then monitor the dok output and make sure that whenever dok is high dcm is also low. in the event that dcm is driven to a higher voltage than dc, the 1m? series resistance limits the current from dcm through the internal diode to dc to a few a. usb input?inear regulator if a valid usb input is present with no valid dc input, current for sys and battery charging is supplied by a low-dropout linear regulator connected from usb to sys. the sys regulation voltage shows the same char- acteristic as when powering from the dc input (see figure 4). the battery charger operates from sys with any extra available current, while not exceeding the maximum-allowed usb current. if both usb and dc inputs are valid, power is only taken from the dc input. the maximum usb input current is set by the logic state of the iusb input to either 100ma or 500ma. power monitor outputs ( uok , dok ) dok is an open-drain, active-low output that indicates the dc input power status. with no source at the usb pin, the source at dc is considered valid and dok is driven low when: 4.15v < v dc < 16v. when the usb voltage is also valid, the dc source is considered valid and dok is driven low when: 4.45v < v dc < 16v. the higher minimum dc voltage with usb present helps guarantee cleaner transitions between input supplies. if the dc power-ok output feature is not required, con- nect dok to ground. uok is an open-drain, active-low output that indicates the usb input power status. uok is low when a valid source is connected at usb. the source at usb is valid when 4.1v < v usb < 6.6v. if the usb power-ok output feature is not required, connect uok to ground. both the uok and the dok circuitry remain active in thermal overload, usb suspend, and when the charger is disabled. dok and uok can also be wire-ored together to generate a single power-ok ( pok) output. thermal limiting when the die temperature exceeds +100c, a thermal limiting circuit reduces the input current limit by 5%/c, bringing the charge current to 0ma at +120c. since the system load gets priority over battery charging, the battery charge current is reduced to 0ma before the input limiter drops the load voltage at sys. to avoid false charge termination, the charge termination detect function is disabled in this mode. if the junction temper- ature rises beyond +120c, no current is drawn from dc or usb, and v sys regulates at 50mv below v bat . system voltage switching dc input when charging from the dc input, if the battery is above the minimum system voltage, sys is connected to the battery. current is provided to both sys and the battery, up to the maximum program value. the step- down output current sense and the charger current sense provide feedback to ensure the current loop demanding the lower input current is satisfied. the advantage of this approach when powering from dc is that power dissipation is dominated by the step-down regulator efficiency, since there is only a small voltage drop from sys to bat. also, load transients can be absorbed by the battery while minimizing the voltage disturbance on sys. if both the dc and usb inputs are valid, the dc input takes priority and delivers the input current, while the usb input is off. after the battery is done charging, the charger is turned off and the sys load current is supplied from the dc input. the sys voltage is regulated to 4.4v. the charg- er turns on again after the battery drops to the restart threshold. if the load current exceeds the input limiter, sys drops down to the battery voltage and the 50m ? sys-to-bat pmos switch turns on to supply the extra load current. the sys-to-bat switch turns off again once the load is below the input current limit. the 50m ? pmos also turns on if valid dc input power is removed. usb input when charging from the usb input, the dc input step- down regulator turns off and a linear regulator from usb to sys powers the system and charges the bat- tery. if the battery is greater than the minimum system i bat x r on 4.2v 4.4v v bat v sysmin v sys v cen = 0v v dc and/or v usb = 5.0v max8903a max8903c figure 4. sys tracking v bat to the minimum system voltage
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 16 ______________________________________________________________________________________ voltage, the sys voltage is connected to the battery. the usb input then supplies the sys load and charges the battery with any extra available current, while not exceeding the maximum-allowed usb current. load transients can be absorbed by the battery while mini- mizing the voltage disturbance on sys. when battery charging is completed, or the charger is disabled, sys is regulated to 4.4v. if both usb and dc inputs are valid, power is only taken from the dc input. usb suspend driving usus high turns off charging as well as the sys output and reduces input current to 170a to accom- modate usb suspend mode. charge enable ( cen ) when cen is low, the charger is on. when cen is high, the charger turns off. cen does not affect the sys out- put. in many systems, there is no need for the system controller (typically a microprocessor) to disable the charger, because the max8903a/max8903c/ max8903d smart power selector circuitry independently manages charging and adapter/battery power hand-off. in these situations, cen may be connected to ground. soft-start to prevent input transients that can cause instability in the usb or ac adapter power source, the rate of change of the input current and charge current is limited. when an input source is valid, sys current is ramped from zero to the set current-limit value in typically 50s. this also means that if dc becomes valid after usb, the sys current limit is ramped down to zero before switch- ing from the usb to dc input. at some point, sys is no longer able to support the load and may switch over to bat. the switchover to bat occurs when v sys < v bat . this threshold is a function of the sys capacitor size and sys load. the sys current limit then ramps from zero to the set current level and sys supports the load again as long as the sys load current is less than the set current limit. power source dok uok dcm*** iusb usus dc step-down output current limit usb input current limit maximum charge current** ac adapter at dc input l x h x x 6000v/r idc lesser of 1200v/r iset and 6000v/r idc l x l l l 100ma lesser of 1200v/r iset and 100ma l x l h l 500ma lesser of 1200v/r iset and 500ma usb power at dc input l x l x h usb suspend usb input off. dc input has priority. 0 h l x l l 100ma lesser of 1200v/r iset and 100ma h l x h l 500ma lesser of 1200v/r iset and 500ma usb power at usb input, dc unconnected h l x x h usb suspend 0 dc and usb unconnected h h x x x no dc input no usb input 0 table 2. input limiter control logic ** charge current cannot exceed the input current limit. charge may be less than the maximum charge current if the total sys load exceeds the input current limit. *** there is an internal diode from dcm (anode) to dc (cathode) as shown in figure 1. if the dcm level needs to be set by a p, us e a mosfet for isolation as shown in figure 3. x = dont care.
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power ______________________________________________________________________________________ 17 when the charger is turned on, the charge current ramps from 0a to the iset current value in typically 1.0ms. charge current also soft-starts when transitioning to fast- charge from prequal, when the input power source is switched between usb and dc, and when changing the usb charge current from 100ma to 500ma with the iusb logic input. there is no di/dt limiting, however, if r iset is changed suddenly using a switch. battery charger while a valid input source is present, the battery charg- er attempts to charge the battery with a fast-charge current determined by the resistance from iset to gnd. calculate the r iset resistance according to the following equation: r iset = 1200v/i chgmax monitoring charge current the voltage from iset to gnd is a representation of the battery charge current and can be used to monitor the current charging the battery. a voltage of 1.5v repre- sents the maximum fast-charge current. if necessary, the charge current is reduced automati- cally to prevent the sys voltage from dropping. therefore, a battery never charges at a rate beyond the capabilities of a 100ma or 500ma usb input, or over- loads an ac adapter. see figure 5. when v bat is below 3v, the charger enters prequal mode and the battery charges at 10% of the maximum fast-charge rate until the voltage of the deeply dis- charged battery recovers. when the battery voltage reaches 4.2v and the charge current drops to 10% of the maximum fast-charge current, the charger enters the done state. the charger restarts a fast-charge cycle if the battery voltage drops by 100mv. charge termination when the charge current falls to the termination thresh- old (i term ) and the charger is in voltage mode, charg- ing is complete. charging continues for a brief 15s top-off period and then enters the done state where charging stops. note that if charge current falls to i term as a result of the input or thermal limiter, the charger does not enter done. for the charger to enter done, charge current must be less than i term , the charger must be in volt- age mode, and the input or thermal limiter must not be reducing charge current. charge status outputs charge output ( chg) chg is an open-drain, active-low output that indicates charger status. chg is low when the battery charger is in its prequalification and fast-charge states. chg goes high impedance if the thermistor causes the charger to go into temperature suspend mode. when used in conjunction with a microprocessor (p), connect a pullup resistor between chg and the logic i/o voltage to indicate charge status to the p. alternatively, chg can sink up to 20ma for an led charge indicator. fault output (flt) flt is an open-drain, active-low output that indicates charger status. flt is low when the battery charger has entered a fault state when the charge timer expires. this can occur when the charger remains in its prequal state for more than 33 minutes or if the charger remains in fast-charge state for more than 660 minutes (see figure 6). to exit this fault state, toggle cen or remove and reconnect the input source. when used in conjunction with a microprocessor (p), connect a pullup resistor between flt and the logic i/o voltage to indicate charge status to the p. alternatively, flt can sink up to 20ma for an led fault indicator. if the flt output is not required, connect flt to ground or leave unconnected. charge timer a fault timer prevents the battery from charging indefi- nitely. the fault prequal and fast-charge timers are con- trolled by the capacitance at ct (c ct ). 1.5 0 monitoring the battery charge current with v iset 0 1200v/r iset battery charging current (a) discharging v iset (v) figure 5. monitoring the battery charge current with the voltage from iset to gnd
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 18 ______________________________________________________________________________________ while in fast-charge mode, a large system load or device self-heating may cause the max8903a/max8903c/ max8903d to reduce charge current. under these cir- cumstances, the fast-charge timer is slowed by 2x if the charge current drops below 50% of the programmed fast-charge level, and suspended if the charge current drops below 20% of the programmed level. the fast- charge timer is not affected at any current if the charger is regulating the bat voltage at 4.2v (i.e., the charger is in voltage mode). vl regulator vl is a 5v linear regulator that powers the max8903s internal circuitry and charges the bst capacitor. vl is used externally to bias the batterys thermistor. vl takes t c f t c f ts prequal ct fst chg ct top off = = = ? ? 33 015 660 015 15 min . min . fault uok and/or dok = low chg = high impedance flt = low i chg = 0ma prequalification uok and/or dok = low chg = low flt = high impedance 0 < v bat < 3v i chg i chgmax /10 done uok and/or dok = 0 chg = high impedance flt = high impedance v batreg + v rstrt < v bat < v batreg i chg = 0ma fast-charge uok and/or dok = low chg = low flt = high impedance 3v < v bat < v batreg i chg i chgmax not ready uok and dok = high impedance chg = high impedance flt = high impedance i chg = 0ma timer > t prequal v bat > 3.0v reset timer v bat < 2.82v reset timer = 0 i chg < i term and v bat = v batreg and thermal or input limit not exceeded; reset timer i chg > i term reset timer v bat < v batreg + v rstrt reset timer timer > 15s uok and/or dok = low cen = 0 reset timer cen = hi or remove and reconnect the input source(s) any state toggle cen or remove and reconnect the input source(s) timer > t fstchg (timer slowed by 2x if i chg < i chgmax /2, and paused if i chg < i chgmax /5 while v bat < 4.2v) top-off uok and/or dok = low chg = high impedance flt = high impedance v bat = v batreg i chg = i term temperature suspend i chg = 0ma uok or dok previous state chg = high impedance flt = high impedance any charging state thm not ok timer suspend thm ok timer resume v bat < 2.82v reset timer figure 6. max8903a charger state flow chart
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power ______________________________________________________________________________________ 19 its input power from usb or dc. when input power is available from both usb and dc, vl takes power from dc. vl is enabled whenever the input voltage at usb or dc is greater than ~1.5v. vl does not turn off when the input voltage is above the overvoltage threshold. similarly, vl does not turn off when the charger is dis- abled (cen = high). connect a 1f ceramic capacitor from vl to gnd. thermistor input (thm) the thm input connects to an external negative tem- perature coefficient (ntc) thermistor to monitor battery or system temperature. charging is suspended when the thermistor temperature is out of range. the charge timers are suspended and hold their state but no fault is indicated. when the thermistor comes back into range, charging resumes and the charge timer continues from where it left off. connecting thm to gnd disables the thermistor monitoring function. table 3 lists the fault temperature of different thermistors. since the thermistor monitoring circuit employs an external bias resistor from thm to vl (r tb , figure 7), the thermistor is not limited only to 10k ? (at +25c). any resistance thermistor can be used as long as the value is equivalent to the thermistors +25c resistance. for example, with a 10k ? at +25c thermistor, use 10k? at r tb , and with a 100k ? at +25c thermistor, use 100k?. for a typical 10k? (at +25c) thermistor and a 10k ? r tb resistor, the charger enters a temperature suspend state when the thermistor resistance falls below 3.97k? (too hot) or rises above 28.7k? (too cold). this corre- sponds to a 0c to +50c range when using a 10k ? ntc thermistor with a beta of 3500. the general relation of thermistor resistance to temperature is defined by the following equation: thm gnd thm out of range disable charger vl cen vl 0.74 vl 0.28 vl 0.03 vl cold hot r tb thermistor circuitry enable thm r t r ts r tp alternate thermistor connection r t all comparators 60mv hysteresis max8903a max8903c max8903d figure 7. thermistor monitor circuitry thermistor ? (k) 3000 3250 3500 3750 4250 r tb (k ? ) (figure 7) 10 10 10 10 10 resistance at +25c (k ? ) 10 10 10 10 10 resistance at +50c (k ? ) 4.59 4.30 4.03 3.78 3316 resistance at 0c (k ? ) 25.14 27.15 29.32 31.66 36.91 nominal hot trip temperature (c) 55 53 50 49 46 nominal cold trip temperature (c) -3 -1 0 2 4.5 table 3. fault temperatures for different thermistors
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 20 ______________________________________________________________________________________ where: r t = the resistance in ? of the thermistor at tempera- ture t in celsius r 25 = the resistance in ? of the thermistor at +25c = the material constant of the thermistor, which typi- cally ranges from 3000k to 5000k t = the temperature of the thermistor in c table 3 shows the max8903a/max8903c/max8903d thm temperature limits for different thermistor material constants. some designs might prefer other thermistor temperature limits. threshold adjustment can be accommodated by changing r tb , connecting a resistor in series and/or in parallel with the thermistor, or using a thermistor with dif- ferent ?. for example, a +45c hot threshold and 0c cold threshold can be realized by using a thermistor with a ? of 4250 and connecting 120k ? in parallel. since the thermistor resistance near 0c is much higher than it is near +50c, a large parallel resistance lowers the cold threshold, while only slightly lowering the hot threshold. conversely, a small series resistance raises the hot threshold, while only slightly raising the cold threshold. raising r tb lowers both the cold and hot thresholds, while lowering r tb raises both thresholds. note that since vl is active whenever valid input power is connected at dc or usb, thermistor bias current flows at all times, even when charging is disabled (cen = high). when using a 10k? thermistor and a 10k? pullup to vl, this results in an additional 250a load. this load can be reduced to 25a by instead using a 100k? thermistor and 100k? pullup resistor. power dissipation inductor selection for step-down dc-dc regulator the max8903 step-down dc-dc regulator implements a control scheme that typically results in a 4mhz nomi- nal switching frequency. when the input voltage decreases to a value near the output voltage, high duty cycle operation occurs and, due to minimum off-time constraints, 4mhz operation is not achievable. the reg- ulator then provides a fixed minimum off-time, peak cur- rent regulation. similarly, when the input voltage is too high to allow 4mhz operation due to minimum on-time constraints, the regulator becomes a fixed minimum on- time valley current regulator. for a given maximum output voltage, the minimum rip- ple current condition occurs at the lowest input voltage provided that the minimum input voltage allows the reg- ulator to maintain 4mhz operation. if the minimum input voltage dictates an off-time less than 100ns, then the minimum ripple condition occurs just before the regula- tor enters fixed minimum off-time operation. to allow the current-mode regulator to provide a low-jitter, stable duty factor operation, the inductor ripple current should be greater than 200ma in the minimum ripple current condition. the maximum allowed output inductance l out_max is therefore obtained using the equations (1) and (2) below. (1) otherwise, where t off is the minimum off-time, v sys(max) is maxi- mum charger output voltage, and v dc(min) is minimum dc input voltage. (2) where l out _ max is the maximum allowed inductance. to obtain a small-sized inductor with acceptable core loss, while providing stable, jitter-free operation, the actual output inductance l out , is obtained by choosing an appropriate ripple factor k, and picking an available inductor in the range of the two values of inductance yielded by equations (3) and (4) which describe the maximum ripple current conditions in the minimum on- l vt a out max sys max off _ () . = 02 () () = ? ? 1t v v off sys max dc min ?? ? ? ? ? 1 4mhz tnsif v v off sys max dc min = ? ? ? ? ? ? ? 100 1 () () , 1 4 100 mhz ns rr e t tc c = + ? ? ? ? ? ? ? ? ? ? ? ? ? 25 1 273 1 298 28-pin 4mm x 4mm thin qfn single-layer pcb multilayer pcb continuous power dissipation 1666.7mw derate 20.8mw/c above +70c 2286mw derate 28.6mw/c above +70c ja 48c/w 35c/w jc 3c/w 3c/w table 4. package thermal characteristics
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power ______________________________________________________________________________________ 21 time and minimum off-time modes. the recommended ripple factor ranges from (0.2 k 0.4) for (2a i dc 1a) designs. (3) where t off is the minimum off-time obtained from (1). (4) where v dc(max) is maximum input voltage, v sys(min) is the minimum charger output voltage, and t on is the on- time at high input voltage, as given by the following equation: (5) otherwise, the saturation current rating of the inductor must be greater than the maximum step-down output current programmed at the idc pin plus one-half the maximum ripple current, as given by equation (6). (6) where i sat is the saturation current rating of the output inductor, i dc is the maximum step-down output current programmed at the idc pin, and il ripple_max is the greater of the ripple currents obtained from (7) and (8). (7) (8) table 5 gives recommended inductors for typical charger applications. example: v dc(min) = 4.5v, v dc(max) = 5.5v, v sys(min) = 3v, v sys(max) = 4.2v, r idc = 3k?, k = 0.2, i dc = 2a (max- imum step-down output current) from (1): t off = 100ns from (2): from (3): from (5): which is greater than the minimum on-time of 70ns. from (4): choose l out = 1h. l vv ns a h out min t on __ (. ) . . = = ? 5 5 3 136 02 2 085 t v v mhz ns on = = 3 55 1 4 136 . l vns a h out min t off __ . . . = = 4 2 100 02 2 105 l vns a h out max _ . . . = = 4 2 100 02 21 il vv t l ripple min t dc max sys min on out on __ () () = () ? il vt l ripple min t sys max off out off __ () = ii il sat dc ripple max >+ _ 2 t v v mhz on sys min dc max ? = 1 4 () () tnsif v v mhz ns on sys min dc max = ? ? ? ? ? ? 70 1 4 70 , () () l vv t ki out min t dc max sys min on dc on __ () () = () ? l vt ki out min t sys max off dc off __ () = dc input voltage range, charging current recommended inductor 4.5v to 5.5v, 2a 1h inductor, 1072as-1r0n, toko, de2818 series, 3.2mm x 3mm x 1.8mm, 25m ? , 2.6a 4.5v to 5.5v, 1a 1.5h inductor, mdt2520-cn1r5m, toko, 2.5mm x 2mm x 1.2mm, 95m? , 1.25a 10.8v to 13.2v, 2a 1h inductor, 1072as-1r0n, toko, de2818 series, 3.2mm x 3mm x 1.8mm, 25m?, 2.6a 10.8v to 13.2v, 1a 2.2h inductor, mdt2520-cn2r2m, toko, 2.5mm x 2mm x 1.2mm, 105m?, 1.20a table 5. recommended inductor examples
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 22 ______________________________________________________________________________________ max8903a max8903c max8903d thin qfn 4mm x 4mm top view 26 27 25 24 10 9 11 pg dc dcm bst iusb 12 pg bat flt usb bat thm usus 12 cs 4567 2021 19 17 16 15 cs lx gnd idc ct vl dc uok 3 18 28 8 lx dok sys 23 13 iset sys 22 14 cen chg + *exposed pad *ep pin configuration chip information process: bicmos package information for the latest package outline information and land patterns, go to www.maxim-ic.com/packages . package type package code document no. 28 tqfn-ep t2844-1 21-0139 from (7): from (8): from (6), the saturation current rating for the inductor: pcb layout and routing good design minimizes ground bounce and voltage gradients in the ground plane, which can result in insta- bility or regulation errors. the gnd and pgs should connect to the power-ground plane at only one point to minimize the effects of power-ground currents. battery ground should connect directly to the power-ground plane. the iset and idc current-setting resistors should connect directly to gnd to avoid current errors. connect gnd to the exposed pad directly under the ic. use multiple tightly spaced vias to the ground plane under the exposed pad to help cool the ic. position input capacitors from dc, sys, bat, and usb to the power-ground plane as close as possible to the ic. keep high current traces such as those to dc, sys, and bat as short and wide as possible. refer to the max8903a/max8903c/max8903d evaluation kit for a suitable pcb layout example. ia a ia sat sat >+ > 2 0 420 2 221 . . il vv ns s ma ripple min t on __ . = () = ? 5 5 3 136 1 341 il vns h ma ripple min t off __ . = = 4 2 100 1 420
max8903a/max8903c/max8903d 2a 1-cell li+ dc-dc chargers for usb and adapter power 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. maxim integrated products, 120 san gabriel drive, sunnyvale, ca 94086 408-737-7600 ____________________ 23 ? 2009 maxim integrated products maxim is a registered trademark of maxim integrated products, inc. revision history revision number revision date description pages changed 0 12/08 initial release 1 8/09 added max8903c/max8903d to data sheet 1C20 2 11/09 made various corrections 1C7, 9, 11C21

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