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ltc3559/ltc3559-1 1 3559fb typical application features applications description linear usb battery charger with dual buck regulators the ltc ? 3559/ltc3559-1 are usb battery chargers with dual high ef? ciency buck regulators. the parts are ideally suited to power single-cell li-ion/polymer based handheld applications needing multiple supply rails. battery charge current is programmed via the prog pin and the hpwr pin, with capability up to 950ma at the bat pin. the battery charger has an ntc input for temperature quali? ed charging. the chrg pin allows battery status to be monitored continuously during the charging process. an internal timer controls charger termination. each monolithic synchronous buck regulator provides up to 400ma of output current while operating at ef? ciencies greater than 90% over the entire li-ion/polymer range. a mode pin provides the ? exibility to place both buck regulators in a power saving burst mode ? operation or a low noise pulse skip mode. the ltc3559/ltc3559-1 are offered in a low pro? le ther- mally enhanced 16-lead (3mm 3mm) qfn package. usb charger plus dual buck regulators battery charger n standalone usb charger n up to 950ma charge current programmable via single resistor n hpwr input selects 20% or 100% of programmed charge current n ntc input for temperature quali? ed charging n internal timer termination n bad battery detection n chrg indicates c/10 or timeout buck regulators n 400ma output current n 2.25mhz constant frequency operation n zero current in shutdown n low noise pulse skip operation or power saving burst mode operation n low no-load quiescent current: 35a n available in a low pro? le thermally enhanced 16-lead 3mm 3mm qfn package n sd/flash-based mp3 players n low power handheld applications v cc ntc chrg prog susp hpwr en1 4.7h 2.2f 10f 309k 655k 649k 324k 10f 22pf 22pf up to 500ma ltc3559 gnd exposed pad 1f 4.7h 1.74k en2 mode bat usb (4.3v to 5.5v) or ac adaptor digital control pv in sw1 fb1 sw2 fb2 2.5v 400ma single li-lon cell (2.7v to 4.2v) 1.2v 400ma 3559 ta01 + l , lt, ltc and ltm are registered trademarks of linear technology corporation. all other trademarks are the property of their respective owners.
ltc3559/ltc3559-1 2 3559fb order information pin configuration electrical characteristics absolute maximum ratings v cc (transient); t < 1ms and duty cycle < 1% ....................... ?0.3v to 7v v cc (static) .................................................. ?0.3v to 6v bat, chrg, susp ........................................ ?0.3v to 6v hpwr, ntc, prog ....... ?0.3v to max (v cc , bat) + 0.3v prog pin current ...............................................1.25ma bat pin current ..........................................................1a pv in ................................................ ?0.3v to bat + 0.3v en1, en2, mode .......................................... ?0.3v to 6v fb1, fb2, sw1, sw2 ............?0.3v to pv in + 0.3v or 6v i sw1 , i sw2 ...................................................... 600ma dc junction temperature (note 2) ............................. 125c operating temperature range (note 3).... ?40c to 85c storage temperature .............................. ?65c to 125c (note 1) 16 15 14 13 5 6 7 8 top view 17 ud package 16-lead (3mm s 3mm) plastic qfn 9 10 11 12 4 3 2 1gnd bat mode fb1 hpwr susp fb2 en2 v cc chrg prog ntc en1 sw1 pv in sw2 t jmax = 125c, ja = 68c/w exposed pad (pin 17) is gnd, must be soldered to pcb the l denotes speci? cations that apply over the full operating temperature range, otherwise speci? cations are at t a = 25c. symbol parameter conditions min typ max units battery charger. v cc = 5v, bat = pv in = 3.6v, r prog = 1.74k, hpwr = 5v, susp = ntc = en1 = en2 = 0v v cc input supply voltage l 4.3 5.5 v i vcc battery charger quiescent current (note 4) standby mode, charge terminated suspend mode, v susp = 5v 200 8.5 400 17 a a v float bat regulated output voltage ltc3559 0c t a 85c, ltc3559 4.179 4.165 4.200 4.200 4.221 4.235 v v ltc3559-1 0c t a 85c, ltc3559-1 4.079 4.065 4.100 4.100 4.121 4.135 v v i chg constant-current mode charge current hpwr = 5v hpwr = 0v l 440 84 460 92 500 100 ma ma i bat battery drain current standby mode, charger terminated shutdown, v cc < v uvlo , bat = v float suspend mode, susp = 5v, bat = v float ?3.5 ?2.5 ?1.5 ?7 ?4 ?3 a a a v uvlo undervoltage lockout threshold bat = 3.5v, v cc rising 3.85 4.0 4.125 v v uvlo undervoltage lockout hysteresis bat = 3.5v 200 mv v duvlo differential undervoltage lockout threshold bat = 4.05v, (v cc ? bat) falling (ltc3559) bat = 3.95v, (v cc ? bat) falling (ltc3559-1) 30 30 50 50 70 70 mv mv lead free finish tape and reel part marking package description temperature range ltc3559eud#pbf ltc3559eud#trpbf lcmb 16-lead (3mm 3mm) plastic qfn ?40c to 85c ltc3559eud-1#pbf ltc3559eud-1#trpbf ldqd 16-lead (3mm 3mm) plastic qfn ?40c to 85c consult ltc marketing for parts speci? ed with wider operating temperature ranges. consult ltc marketing for information on non-standard lead based ? nish parts. for more information on lead free part marking, go to: http://www.linear.com/leadfree/ for more information on tape and reel speci? cations, go to: http://www.linear.com/tapeandreel/
ltc3559/ltc3559-1 3 3559fb symbol parameter conditions min typ max units v duvlo differential undervoltage lockout hysteresis bat = 4.05v (ltc3559) bat = 3.95v (ltc3559-1) 130 130 mv mv v prog prog pin servo voltage hpwr = 5v hpwr = 0v bat < v trkl 1.000 0.200 0.100 v v v h prog ratio of i bat to prog pin current 800 ma/ma i trkl trickle charge current bat < v trkl 36 46 56 ma v trkl trickle charge threshold voltage bat rising 2.8 2.9 3.0 v v trkl trickle charge hysteresis voltage 100 mv v rechrg recharge battery threshold voltage threshold voltage relative to v float C85 C100 C130 mv t rechrg recharge comparator filter time bat falling 1.7 ms t term safety timer termination period bat = v float 3.5 4 4.5 hour t badbat bad battery termination time bat < v trkl 0.4 0.5 0.6 hour h c/10 end-of-charge indication current ratio (note 5) 0.085 0.1 0.11 ma/ma t c/10 end-of-charge comparator filter time i bat falling 2.2 ms r on(chg) battery charger power fet on-resistance (between v cc and bat) i bat = 190ma 500 m t lim junction temperature in constant temperature mode 105 c ntc v cold cold temperature fault threshold voltage rising ntc voltage hysteresis 75 76.5 1.6 78 %v cc %v cc v hot hot temperature fault threshold voltage falling ntc voltage hysteresis 33.4 34.9 1.6 36.4 %v cc %v cc v dis ntc disable threshold voltage falling ntc voltage hysteresis l 0.7 1.7 50 2.7 %v cc mv i ntc ntc leakage current v ntc = v cc = 5v C1 1 a logic (hpwr, susp , chrg ) v il input low voltage hpwr, susp pins 0.4 v v ih input high voltage hpwr, susp pins 1.2 v r dn logic pin pull-down resistance hpwr, susp pins l 1.9 4 6.3 m v chrg chrg pin output low voltage i chrg = 5ma 100 250 mv i chrg chrg pin input current bat = 4.5v, v chrg = 5v 0 1 a buck switching regulators, bat = pv in = 3.8v, en1 = en2 = 3.8v pv in input supply voltage ltc3559 ltc3559-1 l l 3 3 4.2 4.1 v v i pvin pulse skip supply current burst mode supply current shutdown supply current supply current in uvlo mode = 0 (one buck enabled) (note 6) mode = 1 (one buck enabled) (note 6) en1 = en2 = 0v pv in = 2.0v l 220 35 0 4 400 50 2 8 a a a a pv in uvlo pv in falling pv in rising 2.45 2.55 v v f osc switching frequency mode = 0v 1.91 2.25 2.59 mhz v il input low voltage mode, en1, en2 0.4 v v ih input high voltage mode, en1, en2 1.2 v i limsw peak pmos current limit mode = 0v or 3.8v 550 800 1050 ma electrical characteristics the l denotes speci? cations that apply over the full operating temperature range, otherwise speci? cations are at t a = 25c.
ltc3559/ltc3559-1 4 3559fb typical performance characteristics suspend state supply and bat currents vs temperature battery regulation (float) voltage vs temperature battery regulation (float) voltage vs battery charge current, constant-voltage charging note 1: stresses beyond those listed under absolute maximum ratings may cause permanent damage to the device. exposure to any absolute maximum rating condition for extended periods may affect device reliability and lifetime. note 2: t j is calculated from the ambient temperature t a and power dissipation p d according to the following formula: t j = t a + (p d ? ja c/w) note 3: the ltc3559/ltc3559-1 are guaranteed to meet speci? cations from 0c to 85c. speci? cations over the C40c to 85c operating temperature range are assured by design, characterization and correlation with statistical process controls. note 4: v cc supply current does not include current through the prog pin or any current delivered to the bat pin. total input current is equal to this speci? cation plus 1.00125 ? i bat where i bat is the charge current. note 5: i c/10 is expressed as a fraction of measured full charge current with indicated prog resistor. note 6: fb high, regulator not switching. temperature (c) C55 0 current (a) 1 3 4 5 10 7 C15 25 45 3559 g01 2 8 9 i vcc 6 C35 5 65 85 v cc = 5v bat = 4.2v susp = 5v en1 = en2 = 0v i bat temperature (c) C55 v float (v) 4.225 5 3559 g02 4.150 4.100 C35 C15 25 4.075 4.050 4.250 4.200 4.175 4.125 45 65 85 v cc = 5v ltc3559 ltc3559-1 i bat (ma) 100 v bat (v) 4.180 4.190 4.205 4.200 900 3559 g03 4.170 4.160 4.175 4.185 4.195 4.165 4.155 4.150 300 500 700 200 0 400 600 800 1000 v cc = 5v hpwr = 5v r prog = 845 en1 = en2 = 0v symbol parameter conditions min typ max units v fb feedback voltage l 780 800 820 mv i fb fb input current fb1, fb2 = 0.82v C0.05 0.05 a d max maximum duty cycle fb1, fb2 = 0v 100 % r pmos r ds(on) of pmos i sw = 150ma 0.65 r nmos r ds(on) of nmos i sw = C150ma 0.75 r sw(pd) sw pull-down in shutdown 13 k electrical characteristics the l denotes speci? cations that apply over the full operating temperature range, otherwise speci? cations are at t a = 25c.
ltc3559/ltc3559-1 5 3559fb temperature (c) C55 3.9 4.0 4.2 545 3559 g07 3.8 3.7 C35 C15 25 65 85 3.6 3.5 4.1 v cc (v) bat = 3.5v rising falling temperature (c) C55 i bat (a) 2.0 2.5 3.0 545 3559 g08 1.5 1.0 C35 C15 25 65 85 0.5 0 bat = 4.2 (ltc3559) en1 = en2 = 0v bat = 3.6 i bat (ma) 0 v prog (v) 0.4 0.8 1.2 0.2 0.6 1.0 100 200 300 400 3559 g09 500 50 0 150 250 350 450 v cc = 5v hpwr = 5v r prog = 1.74k en1 = en2 = 0v v cc (v) 4.3 440 i bat (ma) 450 460 470 480 500 4.5 4.6 4.9 5.1 3559 g04 5.3 4.4 4.7 4.8 5.0 5.2 5.4 5.5 490 445 455 465 475 495 485 v cc = 5v hpwr = 5v r prog = 1.74k en1 = en2 = 0v battery charge current vs supply voltage battery charge current vs battery voltage (ltc3559) battery charge current vs ambient temperature in thermal regulation typical performance characteristics battery charger undervoltage lockout threshold vs temperature prog voltage vs battery charge current recharge threshold vs temperature battery charger fet on-resistance vs temperature susp/hpwr pin rising thresholds vs temperature v bat (v) 2 i bat (ma) 300 400 500 4 3559 g05 200 100 250 350 450 150 50 0 2.5 3 3.5 4.5 v cc = 5v r prog = 1.74k hpwr = 5v hpwr = 0v temperature (c) C55 0 i bat (ma) 50 150 200 250 500 350 C15 25 45 125 3559 g06 100 400 450 300 C35 5 65 85 105 v cc = 5v hpwr = 5v r prog = 1.74k en1 = en2 = 0 battery drain current in undervoltage lockout vs temperature temperature (c) C55 75 v recharge (mv) 79 87 91 95 115 103 C15 25 45 3559 g10 83 107 111 99 C35 5 65 85 v cc = 5v temperature (c) C55 r on (m) 500 550 600 85 3559 g11 450 400 300 C35 C15 5 25 45 65 350 700 650 v cc = 4v i bat = 200ma en1 = en2 = 0v temperature (c) C55 threshold (v) 1.1 5 3559 g12 0.8 0.6 C35 C15 25 0.5 0.4 1.2 1.0 0.9 0.7 45 65 85 v cc = 5v
ltc3559/ltc3559-1 6 3559fb typical performance characteristics timer accuracy vs temperature complete charge cycle 2400mah battery (ltc3559) buck regulator input current vs temperature, burst mode operation buck regulator input current vs temperature, pulse skip mode (ltc3559) buck regulator pv in undervoltage thresholds vs temperature frequency vs temperature temperature (c) C55 C2 percent error (%) C1 1 2 3 25 7 3559 g16 0 C15 C35 45 65 585 4 5 6 v cc = 5v time (hour) 0 i bat (ma) bat (v) chrg (v) 5.0 200 0 400 800 600 1000 35 3559 g17 3.5 3.0 5.0 4.5 4.0 3.0 4.0 1.0 2.0 0 12 4 6 v cc = 5v r prog = 0.845k hpwr = 5v temperature (c) C55 20 input current (a) 25 35 40 45 C15 25 45 125 3559 g18 30 C35 5 65 85 105 50 v fb = 0.82v pv in = 4.2v pv in = 2.7v temperature (c) C55 100 input current (a) 150 250 300 350 C15 25 45 125 3559 g19 200 C35 5 65 85 105 400 v fb = 0.82v pv in = 4.2v pv in = 2.7v temperature (c) C55 2.25 pv in (v) 2.35 2.55 2.65 2.75 C15 25 45 125 3559 g20 2.45 C35 5 65 85 105 2.85 rising falling temperature (c) C55 1.5 f osc (mhz) 1.6 1.8 1.9 2.0 2.5 2.2 5 45 65 3559 g21 1.7 2.3 2.4 2.1 C35 C15 25 85 105 125 pv in = 3.8v chrg pin output low voltage vs temperature timer accuracy vs supply voltage temperature (c) C55 80 100 140 545 3559 g13 60 40 C35 C15 25 65 85 20 0 120 v chrg (mv) v cc = 5v i chrg = 5ma chrg pin i-v curve chrg (v) 0 70 60 50 40 30 20 10 0 35 3559 g14 12 46 i chrg (ma) v cc = 5v bat = 3.8v v cc (v) 4.3 C1.0 percent error (%) C0.5 0 0.5 1.0 2.0 4.5 4.7 4.9 5.1 3559 g15 5.3 5.5 1.5
ltc3559/ltc3559-1 7 3559fb i load (ma) 30 efficiency (%) 90 100 20 10 80 50 70 60 40 0.1 10 100 1000 3559 g28 0 1 pv in = 2.7v pv in = 4.2v v out = 1.2v burst mode operation pulse skip mode i load (ma) 30 efficiency (%) 90 100 20 10 80 50 70 60 40 0.1 10 100 1000 3559 g25 0 1 burst mode operation pulse skip mode v out = 2.5v pv in = 4.2v buck regulator enable thresholds vs temperature typical performance characteristics buck regulator ef? ciency vs i load (ltc3559) buck regulator load regulation buck regulator ef? ciency vs i load (ltc3559) buck regulator load regulation buck regulator pmos r ds(0n) vs temperature (ltc3559) temperature (c) C55 v en (mv) 800 900 1000 105 3559 g22 700 600 400 C15 25 65 C35 125 5 45 85 500 1200 1100 pv in = 3.8v falling rising temperature (c) C55 400 r ds(on) (m) 500 700 800 900 65 1300 3559 g23 600 5 C35 85 25 C15 105 45 12 5 1000 1100 1200 pv in = 2.7v pv in = 4.2v buck regulator nmos r ds(0n) vs temperature (ltc3559) temperature (c) C55 400 r ds(on) (m) 500 700 800 900 65 1300 3559 g24 600 5 C35 85 25 C15 105 45 12 5 1000 1100 1200 pv in = 2.7v pv in = 4.2v i load (ma) 1 2.52 v out (v) 2.56 2.60 10 100 100 0 3559 g26 2.48 2.50 2.54 2.58 2.46 2.44 burst mode operation pulse skip mode pv in = 3.8v v out = 2.5v pv in (v) 2.7 v out (v) 2.50 2.52 2.54 3.6 4.2 3559 g27 2.48 2.46 2.44 3.0 3.3 3.9 2.56 2.58 2.60 v out = 2.5v i load = 200ma buck regulator line regulation i load (ma) 1 1.19 v out (v) 1.20 1.21 1.22 1.23 10 100 100 0 3559 g29 1.18 1.17 1.16 1.15 1.24 1.25 pv in = 3.8v v out = 1.2v burst mode operation pulse skip mode pv in (v) 2.7 v out (v) 1.21 1.23 1.25 3.9 3559 g30 1.19 1.17 1.20 1.22 1.24 1.18 1.16 1.15 3.0 3.3 3.6 4.2 v out = 1.2v i load = 200ma buck regulator line regulation
ltc3559/ltc3559-1 8 3559fb typical performance characteristics buck regulator start-up transient buck regulator pulse skip mode operation v out 500mv/div en 2v/div pv in = 3.8v pulse skip mode load = 6 50s/div 3559 g33 inductor current i l = 200ma/div buck regulator burst mode operation v out 20mv/div (ac) sw 2v/div pv in = 3.8v load = 10ma 200ns/div 3559 g34 inductor current i l = 50ma/div v out 20mv/div (ac) sw 2v/div pv in = 3.8v load = 60ma 2s/div 3559 g35 inductor current i l = 60ma/div buck regulator transient response, pulse skip mode v out 50mv/div (ac) load step 5ma to 290ma pv in = 3.8v 50s/div 3559 g36 inductor current i l = 200ma/div buck regulator transient response, burst mode operation v out 50mv/div (ac) load step 5ma to 290ma pv in = 3.8v 50s/div 3559 g37 inductor current i l = 200ma/div
ltc3559/ltc3559-1 9 3559fb gnd (pin 1): ground, connect to exposed pad (pin 17). bat (pin 2): charge current output. provides charge cur- rent to the battery and regulates ? nal ? oat voltage to 4.2v (ltc3559) or 4.1v (ltc3559-1). mode (pin 3): mode pin for buck regulators. when held high, both regulators are in burst mode operation. when held low both regulators operate in pulse skip mode. this pin is a high impedance input; do not ? oat. fb1 (pin 4): buck 1 feedback voltage pin. receives feed- back by a resistor divider connected across the output. en1 (pin 5): enable input pin for buck 1. this pin is a high impedance input; do not ? oat. active high. sw1 (pin 6): buck 1 switching node. external inductor connects to this node. pv in (pin 7): input supply pin for buck regulators. connect to bat. a 2.2 f decoupling capacitor to gnd is recommended. sw2 (pin 8): buck 2 switching node. external inductor connects to this node. en2 (pin 9): enable input pin for buck 2. this pin is a high impedance input; do not ? oat. active high. fb2 (pin 10): buck 2 feedback voltage pin. receives feed- back by a resistor divider connected across the output. susp (pin 11): suspend battery charging operation. a voltage greater than 1.2v on this pin puts the battery charger into suspend mode, disables the charger and resets the termination timer. a weak pull-down current is internally applied to this pin to ensure it is low at power up when the input is not being driven externally. hpwr (pin 12): high current battery charging enabled. a voltage greater than 1.2v at this pin programs the bat pin current at 100% of the maximum programmed charge current. a voltage less than 0.4v sets the bat pin current to 20% of the maximum programmed charge current. when used with a 1.74k prog resistor, this pin can toggle between low power and high power modes per usb speci? cation. a weak pull-down current is internally applied to this pin to ensure it is low at power up when the input is not being driven externally. ntc (pin 13): input to the ntc thermistor monitoring circuit. the ntc pin connects to a negative temperature coef? cient thermistor which is typically co-packaged with the battery pack to determine if the battery is too hot or too cold to charge. if the battery temperature is out of range, charging is paused until the battery temperature re-enters the valid range. a low drift bias resistor is re- quired from v cc to ntc and a thermistor is required from ntc to ground. to disable the ntc function, the ntc pin should be grounded. prog (pin 14): charge current program and charge current monitor pin. charge current is programmed by connecting a resistor from prog to ground. when charg- ing in constant-current mode, the prog pin servos to 1v if the hpwr pin is pulled high, or 200mv if the hpwr pin is pulled low. the voltage on this pin always represents the battery current through the following formula: i prog r bat prog = ?800 chrg (pin 15): open-drain charge status output. the chrg pin indicates the status of the battery charger. four possible states are represented by chrg : charging, not charging (i.e., the charge current is less than 1/10th of the full-scale charge current), unresponsive battery (i.e., the battery voltage remains below 2.9v after 1/2 hour of charg- ing) and battery temperature out of range. chrg requires a pull-up resistor and/or led to provide indication. v cc (pin 16): battery charger input. a 1f decoupling capacitor to gnd is recommended. exposed pad (pin 17): ground. the exposed pad must be soldered to pcb ground to provide electrical contact and rated thermal performance. pin functions
ltc3559/ltc3559-1 10 3559fb block diagram 15 C + ta 800x bat 1x t die t die ot ca ntca ntc ref logic chrg 16 2 prog battery charger buck regulator 1 control logic mode en v c v fb clk 0.8v 14 pv in 7 sw1 6 sw2 8 1 17 v cc 12 hpwr 11 susp ntc mode en1 en2 fb1 maxer v in bat body C + g m buck regulator 2 3559 bd control logic mode en v c gnd exposed pad v fb clk 0.8v C + g m undervoltage lockout die temperature bandgap oscillator 2.25mhz v ref clk 13 3 5 9 4 fb2 10
ltc3559/ltc3559-1 11 3559fb operation the ltc3559/ltc3559-1 are linear battery chargers with dual monolithic synchronous buck regulators. the buck regulators are internally compensated and need no external compensation components. the battery charger employs a constant- current/constant- voltage charging algorithm and is capable of charging a single li-ion battery at charging currents up to 950ma. the user can program the maximum charging current available at the bat pin via a single prog resistor. the actual bat pin current is set by the status of the hpwr pin. for proper operation, the bat and pv in pins must be tied together. if a buck regulator is also enabled during the battery charging operation, the net current charging the battery may be lower than the actual programmed value. refer to figure 1 for an explanation. figure 1. current being delivered at the bat pin is 500ma. both buck regulators are enabled. the sum of the average input currents drawn by both buck regulators is 200ma. this makes the effective battery charging current only 300ma. if the hpwr pin were tied lo, the bat pin current would be 100ma. with the buck regulator conditions unchanged, this would cause the battery to discharge at 100ma v cc prog r prog 1.62k susp hpwr en1 2.2f 500ma ltc3559/ ltc3559-1 en2 mode high high high low (pulse skip mode) bat usb (5v) pv in sw1 v out1 single li-lon cell 3.6v sw2 v out2 200ma 300ma 3559 f01 + + applications information battery charger introduction the ltc3559/ltc3559-1 have a linear battery charger designed to charge single-cell lithium-ion batteries. the charger uses a constant-current/constant-voltage charge algorithm with a charge current programmable up to 950ma. additional features include automatic recharge, an internal termination timer, low-battery trickle charge conditioning, bad-battery detection, and a thermistor sensor input for out of temperature charge pausing. furthermore, the battery charger is capable of operating from a usb power source. in this application, charge current can be programmed to a maximum of 100ma or 500ma per usb power speci? cations. input current vs charge current the battery charger regulates the total current delivered to the bat pin; this is the charge current. to calculate the total input current (i.e., the total current drawn from the v cc pin), it is necessary to sum the battery charge current, charger quiescent current and prog pin current. undervoltage lockout (uvlo) the undervoltage lockout circuit monitors the input volt- age (v cc ) and disables the battery charger until v cc rises above v uvlo (typically 4v). 200mv of hysteresis prevents oscillations around the trip point. in addition, a differential undervoltage lockout circuit disables the battery charger when v cc falls to within v duvlo (typically 50mv) of the bat voltage.
ltc3559/ltc3559-1 12 3559fb applications information suspend mode the battery charger can also be disabled by pulling the susp pin above 1.2v. in suspend mode, the battery drain current is reduced to 1.5a and the input current is reduced to 8.5a. charge cycle overview when a battery charge cycle begins, the battery charger ? rst determines if the battery is deeply discharged. if the battery voltage is below v trkl , typically 2.9v, an automatic trickle charge feature sets the battery charge current to 10% of the full-scale value. once the battery voltage is above 2.9v, the battery charger begins charging in constant-current mode. when the battery voltage approaches the 4.2v (ltc3559) or 4.1v (ltc3559-1) required to maintain a full charge, otherwise known as the ? oat voltage, the charge current begins to decrease as the battery charger switches into constant- voltage mode. trickle charge and defective battery detection any time the battery voltage is below v trkl , the charger goes into trickle charge mode and reduces the charge current to 10% of the full-scale current. if the battery voltage remains below v trkl for more than 1/2 hour, the charger latches the bad-battery state, automatically termi- nates, and indicates via the chrg pin that the battery was unresponsive. if for any reason the battery voltage rises above v trkl , the charger will resume charging. since the charger has latched the bad-battery state, if the battery voltage then falls below v trkl again but without rising past v rechrg ? rst, the charger will immediately assume that the battery is defective. to reset the charger (i.e., when the dead battery is replaced with a new battery), simply remove the input voltage and reapply it or put the part in and out of suspend mode. charge termination the battery charger has a built-in safety timer that sets the total charge time for 4 hours. once the battery voltage rises above v rechrg and the charger enters constant-voltage mode, the 4-hour timer is started. after the safety timer expires, charging of the battery will discontinue and no more current will be delivered. automatic recharge after the battery charger terminates, it will remain off, drawing only microamperes of current from the battery. if the portable product remains in this state long enough, the battery will eventually self discharge. to ensure that the battery is always topped off, a charge cycle will automati- cally begin when the battery voltage falls below v rechrg . in the event that the safety timer is running when the battery voltage falls below v rechrg , it will reset back to zero. to prevent brief excursions below v rechrg from resetting the safety timer, the battery voltage must be below v rechrg for more than 1.7ms. the charge cycle and safety timer will also restart if the v cc uvlo or duvlo cycles low and then high (e.g., v cc is removed and then replaced) or the charger enters and then exits suspend mode. programming charge current the prog pin serves both as a charge current program pin, and as a charge current monitor pin. by design, the prog pin current is 1/800th of the battery charge current. therefore, connecting a resistor from prog to ground programs the charge current while measuring the prog pin voltage allows the user to calculate the charge current. full-scale charge current is de? ned as 100% of the con- stant-current mode charge current programmed by the prog resistor. in constant-current mode, the prog pin servos to 1v if hpwr is high, which corresponds to charg- ing at the full-scale charge current, or 200mv if hpwr is low, which corresponds to charging at 20% of the full- scale charge current. thus, the full-scale charge current and desired program resistor for a given full-scale charge current are calculated using the following equations: i v r r v i chg prog prog chg = = 800 800
ltc3559/ltc3559-1 13 3559fb applications information in any mode, the actual battery current can be determined by monitoring the prog pin voltage and using the follow- ing equation: i prog r bat prog = ?800 thermal regulation to prevent thermal damage to the ic or surrounding components, an internal thermal feedback loop will auto- matically decrease the programmed charge current if the die temperature rises to approximately 115c. thermal regulation protects the battery charger from excessive temperature due to high power operation or high ambient thermal conditions and allows the user to push the limits of the power handling capability with a given circuit board design without risk of damaging the ltc3559/ltc3559-1 or external components. the bene? t of the ltc3559/ ltc3559-1 battery charger thermal regulation loop is that charge current can be set according to actual conditions rather than worst-case conditions with the assurance that the battery charger will automatically reduce the current in worst-case conditions. charge status indication the chrg pin indicates the status of the battery charger. four possible states are represented by chrg : charging, not charging, unresponsive battery and battery temperature out of range. the signal at the chrg pin can be easily recognized as one of the above four states by either a human or a micropro- cessor. the chrg pin, which is an open-drain output, can drive an indicator led through a current limiting resistor for human interfacing, or simply a pull-up resistor for microprocessor interfacing. to make the chrg pin easily recognized by both humans and microprocessors, the pin is either low for charging, high for not charging, or it is switched at high frequency (35khz) to indicate the two possible faults: unresponsive battery and battery temperature out of range. when charging begins, chrg is pulled low and remains low for the duration of a normal charge cycle. when the charge current has dropped to below 10% of the full-scale current, the chrg pin is released (high impedance). if a fault occurs after the chrg pin is released, the pin re- mains high impedance. however, if a fault occurs before the chrg pin is released, the pin is switched at 35khz. while switching, its duty cycle is modulated between a high and low value at a very low frequency. the low and high duty cycles are disparate enough to make an led appear to be on or off thus giving the appearance of blinking. each of the two faults has its own unique blink rate for human recognition as well as two unique duty cycles for microprocessor recognition. table 1 illustrates the four possible states of the chrg pin when the battery charger is active. table 1. chrg output pin status frequency modulation (blink) frequency duty cycle charging 0hz 0 hz (lo-z) 100% i bat < c/10 0hz 0 hz (hi-z) 0% ntc fault 35khz 1.5hz at 50% 6.25% to 93.75% bad battery 35khz 6.1hz at 50% 12.5% to 87.5% an ntc fault is represented by a 35khz pulse train whose duty cycle varies between 6.25% and 93.75% at a 1.5hz rate. a human will easily recognize the 1.5hz rate as a slow blinking which indicates the out of range battery temperature while a microprocessor will be able to decode either the 6.25% or 93.75% duty cycles as an ntc fault. if a battery is found to be unresponsive to charging (i.e., its voltage remains below v trkl for over 1/2 hour), the chrg pin gives the battery fault indication. for this fault, a human would easily recognize the frantic 6.1hz fast blinking of the led while a microprocessor would be able to decode either the 12.5% or 87.5% duty cycles as a bad battery fault. although very improbable, it is possible that a duty cycle reading could be taken at the bright-dim transition (low duty cycle to high duty cycle). when this happens the duty cycle reading will be precisely 50%. if the duty cycle reading is 50%, system software should disqualify it and take a new duty cycle reading.
ltc3559/ltc3559-1 14 3559fb ntc thermistor the battery temperature is measured by placing a nega- tive temperature coef? cient (ntc) thermistor close to the battery pack. the ntc circuitry is shown in figure 3. to use this feature, connect the ntc thermistor, r ntc , between the ntc pin and ground, and a bias resistor, r nom , from v cc to ntc. r nom should be a 1% resistor with a value equal to the value of the chosen ntc thermistor at 25c (r25). a 100k thermistor is recommended since thermistor current is not measured by the battery charger and its current will have to be considered for compliance with usb speci? cations. the battery charger will pause charging when the re- sistance of the ntc thermistor drops to 0.54 times the applications information value of r25 or approximately 54k (for a vishay curve 1 thermistor, this corresponds to approximately 40c). if the battery charger is in constant-voltage mode, the safety timer will pause until the thermistor indicates a return to a valid temperature. as the temperature drops, the resistance of the ntc thermistor rises. the battery charger is also designed to pause charging when the value of the ntc thermistor increases to 3.25 times the value of r25. for a vishay curve 1 thermistor, this resistance, 325k, corresponds to approximately 0c. the hot and cold comparators each have approximately 3c of hysteresis to prevent oscillation about the trip point. grounding the ntc pin disables all ntc functionality. if susp < 0.4v and v cc > 4v and v cc > bat + 130mv duvlo, uvlo and suspend disable mode 1/10 full charge current chrg strong pull-down 30 minute timer begins trickle charge mode full charge current chrg strong pull-down constant current mode battery charging suspended chrg pulses ntc fault no charge current chrg pulses defective battery 4-hour termination timer begins constant voltage mode no charge current chrg high impedance standby mode chrg high impedance 3559 f02 bat b 2.9v bat > 2.9v 2.9v < bat < v rechrg 30 minute timeout bat drops below v rechrg 4-hour termination timer resets yes no fault fault no power on 4-hour timeout figure 2. state diagram of the battery charger operation
ltc3559/ltc3559-1 15 3559fb applications information alternate ntc thermistors and biasing the battery charger provides temperature quali? ed charging if a grounded thermistor and a bias resistor are connected to the ntc pin. by using a bias resistor whose value is equal to the room temperature resistance of the thermistor (r25) the upper and lower temperatures are pre-programmed to approximately 40c and 0c, respec- tively (assuming a vishay curve 1 thermistor). the upper and lower temperature thresholds can be ad- justed by either a modi? cation of the bias resistor value or by adding a second adjustment resistor to the circuit. if only the bias resistor is adjusted, then either the upper or the lower threshold can be modi? ed but not both. the other trip point will be determined by the characteristics of the thermistor. using the bias resistor in addition to an adjustment resistor, both the upper and the lower tempera- ture trip points can be independently programmed with the constraint that the difference between the upper and lower temperature thresholds cannot decrease. examples of each technique are given below. ntc thermistors have temperature characteristics which are indicated on resistance-temperature conversion tables. the vishay-dale thermistor nths0603n011-n1003f, used in the following examples, has a nominal value of 100k and follows the vishay curve 1 resistance-temperature characteristic. in the explanation below, the following notation is used. r25 = value of the thermistor at 25c r ntc|cold = value of thermistor at the cold trip point r ntc|hot = value of the thermistor at the hot trip point r cold = ratio of r ntc|cold to r25 r hot = ratio of r ntc|hot to r25 r nom = primary thermistor bias resistor (see figure 3) r1 = optional temperature range adjustment resistor (see figure 4) the trip points for the battery chargers temperature quali- ? cation are internally programmed at 0.349 ? v cc for the hot threshold and 0.765 ? v cc for the cold threshold. therefore, the hot trip point is set when: r rr vv ntc hot nom ntc hot cc cc | | ?.? + = 0 349 and the cold trip point is set when: r rr vv ntc cold nom ntc cold cc cc | | ?.? + = 0 765 3559 f03 r nom 100k r ntc 100k C + C + C + too_cold too_hot ntc_enable 0.765 ? v cc (ntc rising) ntc block 0.349 ? v cc (ntc falling) 13 ntc 16 v cc 0.017 ? v cc (ntc falling) 3559 f04 r nom 105k r ntc 100k C + C + C + too_cold too_hot ntc_enable r1 12.7k 0.765 ? v cc (ntc rising) 0.349 ? v cc (ntc falling) 13 ntc 0.017 ? v cc (ntc falling) 16 v cc figure 3. typical ntc thermistor circuit figure 4. ntc thermistor circuit with additional bias resistor
ltc3559/ltc3559-1 16 3559fb applications information solving these equations for r ntc|cold and r ntc|hot results in the following: r ntc|hot = 0.536 ? r nom and r ntc|cold = 3.25 ? r nom by setting r nom equal to r25, the above equations result in r hot = 0.536 and r cold = 3.25. referencing these ratios to the vishay resistance-temperature curve 1 chart gives a hot trip point of about 40c and a cold trip point of about 0c. the difference between the hot and cold trip points is approximately 40c. by using a bias resistor, r nom , different in value from r25, the hot and cold trip points can be moved in either direction. the temperature span will change somewhat due to the nonlinear behavior of the thermistor. the following equations can be used to easily calculate a new value for the bias resistor: r r r r r r nom hot nom cold = = 0 536 25 325 25 . ? . ? where r hot and r cold are the resistance ratios at the de- sired hot and cold trip points. note that these equations are linked. therefore, only one of the two trip points can be chosen, the other is determined by the default ratios designed in the ic. consider an example where a 60c hot trip point is desired. from the vishay curve 1 r-t characteristics, r hot is 0.2488 at 60c. using the above equation, r nom should be set to 46.4k. with this value of r nom , the cold trip point is about 16c. notice that the span is now 44c rather than the previous 40c. the upper and lower temperature trip points can be inde- pendently programmed by using an additional bias resistor as shown in figure 4. the following formulas can be used to compute the values of r nom and r 1 : r rr r rrr nom cold hot nom hot = = ? . ? .? ? ? 2 714 25 1 0 536 r r25 for example, to set the trip points to 0c and 45c with a vishay curve 1 thermistor choose: rkk nom == 3 266 0 4368 2 714 100 104 2 .?. . ?. the nearest 1% value is 105k. r1 = 0.536 ? 105k C 0.4368 ? 100k = 12.6k the nearest 1% value is 12.7k. the ? nal solution is shown in figure 4 and results in an upper trip point of 45c and a lower trip point of 0c. usb and wall adapter power although the battery charger is designed to draw power from a usb port to charge li-ion batteries, a wall adapter can also be used. figure 5 shows an example of how to combine wall adapter and usb power inputs. a p-channel mosfet, mp1, is used to prevent back conduction into the usb port when a wall adapter is present and schottky diode, d1, is used to prevent usb power loss through the 1k pull-down resistor. typically, a wall adapter can supply signi? cantly more current than the 500ma-limited usb port. therefore, an n-channel mosfet, mn1, and an extra program resistor are used to increase the maximum charge current to 950ma when the wall adapter is present. v cc mp1 mn1 1k 1.74k 1.65k i bat li-ion batter y 3559 f05 battery charger bat usb power 500ma i chg 5v wall adapter 950ma i chg prog + d1 figure 5. combining wall adapter and usb power
ltc3559/ltc3559-1 17 3559fb power dissipation the conditions that cause the ltc3559/ltc3559-1 to reduce charge current through thermal feedback can be approximated by considering the power dissipated in the ic. for high charge currents, the ltc3559/ltc3559-1 power dissipation is approximately: pvv i d cc bat bat = () ?? where p d is the power dissipated, v cc is the input supply voltage, v bat is the battery voltage, and i bat is the charge current. it is not necessary to perform any worst-case power dissipation scenarios because the ltc3559/ltc3559-1 will automatically reduce the charge current to maintain the die temperature at approximately 105c. however, the approximate ambient temperature at which the thermal feedback begins to protect the ic is: tcp tcvvi adja a cc bat bat ja = = () 105 105 ? ?? ?? example: consider an ltc3559/ltc3559-1 operating from a usb port providing 500ma to a 3.5v li-ion battery. the ambient temperature above which the ltc3559/ ltc3559-1 will begin to reduce the 500ma charge cur- rent is approximately: tcvvmacw tc a a = ()() = 105 5 3 5 500 68 105 0 ??.? ? / ?.. ? / ? 75 68 105 51 54 wcw c tc a = = the ltc3559/ltc3559-1 can be used above 70c, but the charge current will be reduced from 500ma. the approximate current at a given ambient temperature can be calculated: i ct vv bat a cc bat ja = () 105 ? ?? using the previous example with an ambient tem- perature of 88c, the charge current will be reduced to approximately: i cc vv cw c ca bat = () = 105 88 535 68 17 102 ? ?. ? / / i ima bat = 167 applications information furthermore, the voltage at the prog pin will change proportionally with the charge current as discussed in the programming charge current section. it is important to remember that ltc3559/ltc3559-1 applications do not need to be designed for worst-case thermal conditions since the ic will automatically reduce power dissipation when the junction temperature reaches approximately 105c. battery charger stability considerations the ltc3559/ltc3559-1 battery charger contains two control loops: the constant-voltage and constant-cur- rent loops. the constant-voltage loop is stable without any compensation when a battery is connected with low impedance leads. excessive lead length, however, may add enough series inductance to require a bypass capacitor of at least 1.5f from bat to gnd. furthermore, a 4.7f capacitor with a 0.2 to 1 series resistor from bat to gnd is required to keep ripple voltage low when the bat- tery is disconnected. high value capacitors with very low esr (especially ceramic) reduce the constant-voltage loop phase margin, possibly resulting in instability. ceramic capacitors up to 22f may be used in parallel with a battery, but larger ceramics should be decoupled with 0.2 to 1 of series resistance. in constant-current mode, the prog pin is in the feedback loop, not the battery. because of the additional pole created by the prog pin capacitance, capacitance on this pin must be kept to a minimum. with no additional capacitance on the prog pin, the charger is stable with program resistor values as high as 25k. however, additional capacitance on this node reduces the maximum allowed program resistor. the pole frequency at the prog pin should be kept above 100khz. therefore, if the prog pin is loaded with a capacitance, c prog , the following equation should be used to calculate the maximum resistance value for r prog : r c prog prog 1 210 5 ??
ltc3559/ltc3559-1 18 3559fb applications information average, rather than instantaneous, battery current may be of interest to the user. for example, if a switching power supply operating in low-current mode is connected in parallel with the battery, the average current being pulled out of the bat pin is typically of more interest than the instantaneous current pulses. in such a case, a simple rc ? lter can be used on the prog pin to measure the average battery current as shown in figure 6. a 10k resistor has been added between the prog pin and the ? lter capacitor to ensure stability. the current from building up in the cable too fast thus dampening out any resonant overshoot. buck switching regulator general information the ltc3559/ltc3559-1 contain two 2.25mhz constant- frequency current mode switching regulators that provide up to 400ma each. both switchers can be programmed for a minimum output voltage of 0.8v and can be used to power a microcontroller core, microcontroller i/o, memory or other logic circuitry. both regulators support 100% duty cycle operation (dropout mode) when the input voltage drops very close to the output voltage and are also capable of operating in burst mode operation for highest ef? ciencies at light loads (burst mode operation is pin selectable). the switching regulators also include soft-start to limit inrush current when powering on, short circuit current protection, and switch node slew limiting circuitry to reduce radiated emi. a single mode pin sets both regulators in burst mode operation or pulse skip operating mode while each regula- tor is enabled individually through their respective enable pins en1 and en2. the buck regulators input supply (pv in ) should be connected to the battery pin (bat). this allows the undervoltage lockout circuit on the bat pin to disable the buck regulators when the bat voltage drops below 2.45v. do not drive the buck switching regulators from a voltage other than bat. a 2.2f decoupling capacitor from the pv in pin to gnd is recommended. buck switching regulator output voltage programming both switching regulators can be programmed for output voltages greater than 0.8v. the output voltage for each buck switching regulator is programmed using a resistor divider from the switching regulator output connected to the feedback pins (fb1 and fb2) such that: v out = 0.8(1 + r1/r2) typical values for r1 are in the range of 40k to 1m. the capacitor c fb cancels the pole created by feedback re- sistors and the input capacitance of the fb pin and also helps to improve transient response for output voltages much greater than 0.8v. a variety of capacitor sizes can be used for c fb but a value of 10pf is recommended for 3559 f06 c filter charge current monitor circuitry r prog ltc3559/ ltc3559-1 prog gnd 10k figure 6. isolated capacitive load on prog pin and filtering usb inrush limiting when a usb cable is plugged into a portable product, the inductance of the cable and the high-q ceramic input capacitor form an l-c resonant circuit. if there is not much impedance in the cable, it is possible for the voltage at the input of the product to reach as high as twice the usb voltage (~10v) before it settles out. in fact, due to the high voltage coef? cient of many ceramic capacitors (a nonlinearity), the voltage may even exceed twice the usb voltage. to prevent excessive voltage from damaging the ltc3559/ltc3559-1 during a hot insertion, the soft connect circuit in figure 7 can be employed. in the circuit of figure 7, capacitor c1 holds mp1 off when the cable is ? rst connected. eventually c1 begins to charge up to the usb voltage applying increasing gate support to mp1. the long time constant of r1 and c1 prevents figure 7. usb soft connect circuit r1 40k 5v usb input 3559 f07 c1 100nf c2 10f mp1 si2333 usb cable v cc gnd ltc3559/ ltc3559-1
ltc3559/ltc3559-1 19 3559fb applications information most applications. experimentation with capacitor sizes between 2pf and 22pf may yield improved transient response if so desired by the user. buck switching regulator operating modes the step-down switching regulators include two possible operating modes to meet the noise/power needs of a variety of applications. in pulse skip mode, an internal latch is set at the start of every cycle, which turns on the main p-channel mosfet switch. during each cycle, a current comparator compares the peak inductor current to the output of an error ampli? er. the output of the current comparator resets the internal latch, which causes the main p-channel mosfet switch to turn off and the n-channel mosfet synchronous recti? er to turn on. the n-channel mosfet synchronous recti? er turns off at the end of the 2.25mhz cycle or if the current through the n-channel mosfet synchronous recti? er drops to zero. using this method of operation, the error ampli? er adjusts the peak inductor current to deliver the required output power. all necessary compensation is internal to the step-down switching regulator requiring only a single ceramic output capacitor for stability. at light loads in pulse skip mode, the inductor current may reach zero on each pulse which will turn off the n-channel mosfet synchronous recti? er. in this case, the switch node (sw1 or sw2) goes high impedance and the switch node voltage will ring. this is discontinuous operation, and is normal behavior for a switching regulator. at very light loads in pulse skip mode, the step-down switching regulators will automatically skip pulses as needed to maintain output regulation. at high duty cycle (v out > pv in /2) in pulse skip mode, it is possible for the inductor current to reverse causing the buck converter to switch continuously. regulation and low noise operation are maintained but the input supply current will increase to a couple ma due to the continuous gate switching. during burst mode operation, the step-down switching regulators automatically switch between ? xed frequency pwm operation and hysteretic control as a function of the load current. at light loads the step-down switching regulators control the inductor current directly and use a hysteretic control loop to minimize both noise and switching losses. during burst mode operation, the output capacitor is charged to a voltage slightly higher than the regulation point. the step-down switching regulator then goes into sleep mode, during which the output capacitor provides the load current. in sleep mode, most of the switching regulators circuitry is powered down, helping conserve battery power. when the output voltage drops below a pre-determined value, the step-down switching regulator circuitry is powered on and another burst cycle begins. the sleep time decreases as the load current increases. beyond a certain load current point (about 1/4 rated output load current) the step-down switching regulators will switch to a low noise constant frequency pwm mode of operation, much the same as pulse skip operation at high loads. for applications that can tolerate some output ripple at low output currents, burst mode operation provides better ef? ciency than pulse skip at light loads. the step-down switching regulators allow mode transition on-the-? y, providing seamless transition between modes even under load. this allows the user to switch back and forth between modes to reduce output ripple or increase low current ef? ciency as needed. burst mode operation is set by driving the mode pin high, while pulse skip mode is achieved by driving the mode pin low. buck switching regulator in shutdown the buck switching regulators are in shutdown when not enabled for operation. in shutdown, all circuitry in the buck switching regulator is disconnected from the regulator input supply, leaving only a few nanoamps of + pwm control gnd en mode 0.8v mn fb mp c fb v out p vin c o r1 r2 l sw 3559 f08 figure 8. buck converter application circuit
ltc3559/ltc3559-1 20 3559fb applications information leakage pulled to ground through a 10k resistor on the switch (sw1 or sw2) pin when in shutdown. buck switching regulator dropout operation it is possible for a step-down switching regulators input voltage to approach its programmed output voltage (e.g., a battery voltage of 3.4v with a programmed output voltage of 3.3v). when this happens, the pmos switch duty cycle increases until it is turned on continuously at 100%. in this dropout condition, the respective output voltage equals the regulators input voltage minus the voltage drops across the internal p-channel mosfet and the inductor. buck switching regulator soft-start operation soft-start is accomplished by gradually increasing the peak inductor current for each switching regulator over a 500 s period. this allows each output to rise slowly, helping minimize the battery in-rush current required to charge up the regulators output capacitor. a soft-start cycle occurs whenever a switcher ? rst turns on, or after a fault condition has occurred (thermal shutdown or uvlo). a soft-start cycle is not triggered by changing operating modes using the mode pin. this allows seamless output operation when transitioning between operating modes. buck switching regulator switching slew rate control the buck switching regulators contain circuitry to limit the slew rate of the switch node (sw1 and sw2). this circuitry is designed to transition the switch node over a period of a couple of nanoseconds, signi? cantly reducing radiated emi and conducted supply noise while maintaining high ef? ciency. buck switching regulator low supply operation an undervoltage lockout (uvlo) circuit on pv in shuts down the step-down switching regulators when bat drops below 2.45v. this uvlo prevents the step-down switching regulators from operating at low supply voltages where loss of regulation or other undesirable operation may occur. buck switching regulator inductor selection the buck regulators are designed to work with inductors in the range of 2.2h to 10h, but for most applications a 4.7h inductor is suggested. larger value inductors reduce ripple current which improves output ripple voltage. lower value inductors result in higher ripple current which improves transient response time. to maximize ef? ciency, choose an inductor with a low dc resistance. for a 1.2v output ef? ciency is reduced about 2% for every 100m series resistance at 400ma load current, and about 2% for every 300m series resistance at 100ma load current. choose an inductor with a dc current rating at least 1.5 times larger than the maximum load current to ensure that the inductor does not saturate during normal operation. if output short circuit is a possible condition the induc- tor should be rated to handle the maximum peak current speci? ed for the buck regulators. different core materials and shapes will change the size/cur- rent and price/current relationship of an inductor. toroid or shielded pot cores in ferrite or permalloy materials are small and dont radiate much energy, but generally cost more than powdered iron core inductors with similar electrical characteristics. inductors that are very thin or have a very small volume typically have much higher dcr losses, and will not give the best ef? ciency. the choice of which style inductor to use often depends more on the price vs size, performance, and any radiated emi requirements than on what the buck regulator requires to operate. the inductor value also has an effect on burst mode operation. lower inductor values will cause burst mode switching frequency to increase. table 2 shows several inductors that work well with the ltc3559/ltc3559-1. these inductors offer a good compro- mise in current rating, dcr and physical size. consult each manufacturer for detailed information on their entire selection of inductors.
ltc3559/ltc3559-1 21 3559fb table 2 recommended inductors inductor type l (h) max i dc (a) max dcr( ) size in mm (l w h) manufacturer db318c d312c de2812c 4.7 3.3 4.7 3.3 4.7 3.3 1.07 1.20 0.79 0.90 1.15 1.37 0.1 0.07 0.24 0.20 0.13* 0.105* 3.8 3.8 1.8 3.8 3.8 1.8 3.6 3.6 1.2 3.6 3.6 1.2 3.0 2.8 1.2 3.0 2.8 1.2 toko www.toko.com cdrh3d16 cdrh2d11 cls4d09 4.7 3.3 4.7 3.3 4.7 0.9 1.1 0.5 0.6 0.75 0.11 0.085 0.17 0.123 0.19 4 4 1.8 4 4 1.8 3.2 3.2 1.2 3.2 3.2 1.2 4.9 4.9 1 sumida www.sumida.com sd3118 sd3112 sd12 sd10 4.7 3.3 4.7 3.3 4.7 3.3 4.7 3.3 1.3 1.59 0.8 0.97 1.29 1.42 1.08 1.31 0.162 0.113 0.246 0.165 0.117* 0.104* 0.153* 0.108* 3.1 3.1 1.8 3.1 3.1 1.8 3.1 3.1 1.2 3.1 3.1 1.2 5.2 5.2 1.2 5.2 5.2 1.2 5.2 5.2 1.0 5.2 5.2 1.0 cooper www.cooperet.com lps3015 4.7 3.3 1.1 1.3 0.2 0.13 3.0 3.0 1.5 3.0 3.0 1.5 coilcraft www.coilcraft.com *typical dcr buck switching regulator input/output capacitor selection low esr (equivalent series resistance) ceramic capaci- tors should be used at both switching regulator outputs as well as the switching regulator input supply. only x5r or x7r ceramic capacitors should be used because they retain their capacitance over wider voltage and temperature ranges than other ceramic types. a 10 f output capacitor is suf? cient for most applications. for good transient response and stability the output capacitor should retain at least 4 f of capacitance over operating temperature and bias voltage. the switching regulator input supply should be bypassed with a 2.2 f capacitor. consult manufacturer for detailed information on their selection and speci? cations of ceramic capaci- tors. many manufacturers now offer very thin (< 1mm tall) ceramic capacitors ideal for use in height-restricted designs. table 3 shows a list of several ceramic capacitor manufacturers. applications information table 3: recommended ceramic capacitor manufacturers avx (803) 448-9411 www.avxcorp.com murata (714) 852-2001 www.murata.com taiyo yuden (408) 537-4150 www.t-yuden.com tdk (888) 835-6646 www.tdk.com pcb layout considerations as with all dc/dc regulators, careful attention must be paid while laying out a printed circuit board (pcb) and to component placement. the inductors, input pv in capacitor and output capacitors must all be placed as close to the ltc3559/ltc3559-1 as possible and on the same side as the ltc3559/ltc3559-1. all connections must be made on that same layer. place a local unbroken ground plane below these components that is tied to the exposed pad (pin 17) of the ltc3559/ltc3559-1. the exposed pad must also be soldered to system ground for proper operation.
ltc3559/ltc3559-1 22 3559fb the output voltage of a buck regulator is programmed for 3.3v. when bat voltage approaches 3.3v, the regulator operates in dropout and the output voltage will be bat C (i load ? 0.6). an led at chrg gives a visual indication of the battery charger state. a 3-resistor bias network for ntc sets hot and cold trip points at approximately 55c and 0c v cc ntc chrg prog susp hpwr en1 4.7h 2.2f 10f 324k 1.02m 649k 806k 10f 22pf 22pf up to 950ma ltc3559/ ltc3559-1 gnd exposed pad 1f 110k 510 100k ntc nth50603n01 4.7h 887 en2 mode bat adapter 4.5v to 5.5v pv in sw1 fb1 sw2 digitally controlled fb2 single li-lon cell 2.7v to 4.2v (ltc3559) 2.7v to 4.1v (ltc3559-1) 1.8v at 400ma 3.3v at 400ma 28.7k 3559 ta03 + typical applications buck regulator ef? ciency vs i load buck regulator ef? ciency vs i load i load (ma) 30 efficiency (%) 90 100 20 10 80 50 70 60 40 0.1 10 100 1000 3559 ta02b 0 1 pv in = 2.7v pv in = 4.2v v out = 1.8v burst mode operation pulse skip mode i load (ma) 30 efficiency (%) 90 100 20 10 80 50 70 60 40 0.1 10 100 1000 3559 ta02c 0 1 pv in = 4.2v v out = 3.3v burst mode operation pulse skip mode
ltc3559/ltc3559-1 23 3559fb package description ud package 16-lead plastic qfn (3mm 3mm) (reference ltc dwg # 05-08-1691) the battery can be charged with up to 950ma of charge current. buck regulator 2 is enabled only after v out1 is up to approximately 0.7v. this provides a sequencing function which may be desirable in applications where a microprocessor needs to be powered up before peripherals. chrg interfaces to a microprocessor which decodes the battery charger state v cc ntc chrg prog susp hpwr en1 4.7h 2.2f 10f 10f 309k 655k 649k 324k 22pf 22pf up to 950ma ltc3559/ ltc3559-1 gnd exposed pad 1f 100k 100k ntc nth50603no1 4.7h 887 en2 mode bat 100k adapter 4.5v to 5.5v to microprocessor pv in sw1 fb1 sw2 digitally controlled fb2 single li-lon cell 2.7v to 4.2v (ltc3559) 2.7v to 4.1v (ltc3559-1) 1.2v at 400ma 2.5v at 400ma 3559 ta02 + typical applications 3.00 p 0.10 (4 sides) note: 1. drawing conforms to jedec package outline mo-220 variation (weed-2) 2. drawing not to scale 3. all dimensions are in millimeters 4. dimensions of exposed pad on bottom of package do not include mold flash. mold flash, if present, shall not exceed 0.15mm on any side 5. exposed pad shall be solder plated 6. shaded area is only a reference for pin 1 location on the top and bottom of package pin 1 top mark (note 6) 0.40 p 0.10 bottom viewexposed pad 1.45 p 0.10 (4-sides) 0.75 p 0.05 r = 0.115 typ 0.25 p 0.05 1 pin 1 notch r = 0.20 typ or 0.25 s 45 o chamfer 15 16 2 0.50 bsc 0.200 ref 0.00 C 0.05 (ud16) qfn 0904 recommended solder pad pitch and dimensions 1.45 p 0.05 (4 sides) 2.10 p 0.05 3.50 p 0.05 0.70 p 0.05 0.25 p 0.05 0.50 bsc package outline information furnished by linear technology corporation is believed to be accurate and reliable. however, no responsibility is assumed for its use. linear technology corporation makes no representa- tion that the interconnection of its circuits as described herein will not infringe on existing patent rights.
ltc3559/ltc3559-1 24 3559fb linear technology corporation 1630 mccarthy blvd., milpitas, ca 95035-7417 (408) 432-1900 fax: (408) 434-0507 www.linear.com ? linear technology corporation 2007 lt 0508 rev b ? printed in usa related parts part number description comments ltc3550 dual input usb/ac adapter li-ion battery charger with adjustable output 600ma buck converter synchronous buck converter, ef? ciency: 93%, adjustable output at 600ma, charge current: 950ma programmable, usb compatible, automatic input power detection and selection ltc3552 standalone linear li-ion battery charger with adjustable output dual synchronous buck converter synchronous buck converter, ef? ciency: >90%, adjustable outputs at 800ma and 400ma, charge current programmable up to 950ma, usb compatible, 5mm 3mm dfn16 package ltc3552-1 standalone linear li-ion battery charger with dual synchronous buck converter synchronous buck converter, ef? ciency: >90%, outputs 1.8v at 800ma and 1.575 at 400ma, charge current programmable up to 950ma, usb compatible ltc3455 dual dc/dc converter with usb power manager and li-ion battery charger seamless transition between input power sources: li-ion battery, usb and 5v wall adapter, two high ef? ciency dc/dc converters: up to 96%, full-featured li-ion battery charger with accurate usb current limiting (500ma/100ma) pin-selectable burst mode operation, hot swap tm output for sdio and memory cards, 4mm 4mm qfn24 package ltc3456 2-cell, multi-output dc/dc converter with usb power manager seamless transition between 2-cell battery, usb and ac wall adapter input power sources, main output: fixed 3.3v output, core output: adjustable from 0.8v to v batt(min) , hot swap output for memory cards, power supply sequencing: main and hot swap accurate usb current limiting, high frequency operation: 1mhz, high ef? ciency: up to 92%, 4mm 4mm qfn24 package ltc4080 500ma standalone charger with 300ma synchronous buck charges single-cell li-ion batteries, timer termination +c/10, thermal regulation, buck output: 0.8v to v bat , buck input v in : 2.7v to 5.5v, 3mm 3mm dfn10 package hot swap is a trademark of linear technology corporation.

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