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mp2619 2a, 24v input, 600khz 2-3 cell switching li-ion battery charger with system power path management mp2619 rev. 1.01 www.monolithicpower.com 1 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. the future of analog ic technology description the mp2619 is a monolithic switching charger for 2-3 cell li-ion battery packs with a built in internal power mosfet. it achieves up to 2a charge current with current mode control for fast loop response and easy compensation. the charge current can be programmed by sensing the current through an accurate sense resistor. mp2619 regulates the battery voltage and charge current using two control loops to realize high accuracy cc charge and cv charge. the system power path management function ensures continuous supply to the system by automatically selecting the input or the battery to power the system. power path management separates charging current from system load. when the mp2619 realizes current sharing of the input current, charge current will drop down according to the increase of the system current. fault condition protection includes cycle -by -cycle current limiting, and thermal shutdown. other safety features include battery temperature monitoring, charge status indication and programmable timer to finish the charging cycle. the mp2619 is available in a 28-pin, 4mm x 5mm qfn package. features ? charges 2-3 cell li-ion battery packs ? wide operating input range ? up to 2a programmable charging current ? power path management with current sharing ? 0.75% v batt accuracy ? 0.2 ? internal power mosfet switch ? up to 90% efficiency ? fixed 600khz frequency ? preconditioning for fully depleted batteries ? charging operation indicator ? input supply and battery fault indicator ? thermal shutdown ? cycle-by-cycle over current protection ? battery temperature monitor and protection applications ? netbook pc ? distributed power systems ? chargers for 2-cell or 3-cell li-ion batteries ? pre-regulator for linear regulators all mps parts are lead-free and adhere to the rohs directive. for mps green status, please visit mps website under products, quality assurance page. ?mps? and ?the future of analog ic technology? are registered trademarks o f monolithic power systems, inc.
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 2 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. typical application mp2619 shdn compv compi gnd tmr en r3 10k r ntc 10k c3 10f ntc vref25 vref33 cells ain c1 10f c2 4.7f c10 10f v in pin chgok acok vcc led1 led2 r1 510 r2 510 rg1 51 rs2 rg2 51 20m r4 2.7k c4 2.2nf r5 750 c5 2.2nf rg1 rg2 sw bst c7 0.1f d1 4.7f out1 csp batt rgs1 280 110m rgs2 280 rs1 l c9 22uf v sys v bat c8 22uf m2 m1 m3 c tmr 0.1uf 2/3 cells battery power path on/off charge on/off
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 3 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. ordering information part number* package top marking mp2619ev qfn-28 (4mmx5mm) mp2619 * for tape & reel, add suffix ?z (eg. mp2619ev?z). for rohs compliant packaging, add suffix ?lf (eg. mp2619ev?lf?z) package reference top view 1 2 3 4 5 6 7 8 22 21 20 19 18 17 16 15 9 1011121314 28 27 26 25 24 23 n/c chgok pin sw ain n/c gnd csp rg1 n/c gnd n/c out1 rg2 en shdn sw bst tmr n/c vref33 batt cells compv vcc ntc acok compi absolute maxi mum ratings (1) supply voltage v in ....................................... 26v v sw ....................................... ?0.3v to v in + 0.3v v bs ....................................................... v sw + 6v v csp , v batt , ..................................?0.3v to +18v all other pins .................................?0.3v to +6v continuous power dissipation (t a = +25c) (2) ............................................................. 3.1w junction temperature ...............................150 ? c lead temperature ....................................260 ? c storage temperature.............. ?65 ? c to +150 ? c vcc, rg1, rg2 to gnd..............?0.3v to +42v max differential input voltage, rg1 to rg2...5v recommended operating conditions (3) supply voltage v in ...........................5.5v to 24v output voltage v out .........................0.8v to 20v vcc, rg1, rg2 to gnd .................2.5v to 40v operating junction temp. (t j ). -40c to +125c thermal resistance (4) ja jc qfn-28 (4mmx5mm) ..............40 ....... 9 .... ? c/w notes: 1) exceeding these ratings may damage the device. 2) the maximum allowable power dissipation is a function of the maximum junction temperature t j (max), the junction-to- ambient thermal resistance ja , and the ambient temperature t a . the maximum allowable continuous power dissipation at any ambient temperature is calculated by p d (max) = (t j (max)-t a )/ ja . exceeding the maximum allowable powe r dissipation will cause excessive die temperature, and the regulator will go into thermal shutdown. internal thermal shutdown circuitry protects the device from permanent damage. 3) the device is not guaranteed to function outside of its operating conditions. 4) measured on jesd51-7, 4-layer pcb
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 4 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. electrical characteristics v in = 19v, t a = +25 ? c, cells=0v, unless otherwise noted. parameters symbol condition min typ max units cells=0v 8.337 8.4 8.463 terminal battery voltage v batt cells= float 12.505 12.6 12.695 v csp, batt current i csp ,i batt charging disabled 1 a switch on resistance r ds(on) 0.2 ? switch leakage en = 4v, v sw = 0v 0 1 a cc mode 4.1 a peak current limit trickle mode 2 a cc current i cc rs1=100m ? 1.8 2.0 2.2 a trickle charge current i trickle 10% icc trickle charge voltage threshold 3.0 v/cell trickle charge hysteresis 350 mv/cell termination current threshold i bf 5% 10% 15% icc oscillator frequency f sw cells=0v, v batt =7v 600 khz fold-back frequency v batt = 0v 190 khz maximum duty cycle 90 % maximum current sense voltage (csp to batt) v sense 170 200 230 mv under voltage lockout threshold rising 3 3.2 3.4 v under voltage lockout threshold hysteresis 200 1000 mv open-drain sink current vdrain=0.3v 5 ma dead-battery indicator stay at trickle charge, c tmr =0.1f 30 min recharge threshold at vbatt vrechg 4.0 v/cell recharge hysteresis 100 mv/cell ntc low-temp rising threshold r ntc =ncp18x103, 0c 70.5 73.5 76.5 %of vref33 ntc high-temp falling threshold r ntc =ncp18x103, 50c 27.5 29.5 31.5 %of vref33 vin min head-room (reverse blocking) vin-vbatt 180 mv en input low voltage 0.4 v en input high voltage 1.8 v en = 4v 4 en input current en = 0v 0.2 a
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 5 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. electrical characteristics (continued) v in = 19v, t a = +25 ? c, cells=0v, unless otherwise noted. parameters symbol condition min typ max units en = 4v 0.5 ma supply current (shutdown) en = 4v, consider vref33 pin output current. r 3 =10k,r ntc =10k 0.665 ma supply current (quiescent) i ain en = 0v, cells=0v, vbatt=4.5v 2.0 ma thermal shutdown (5) 150 c vref33 output voltage 3.3 v vref33 load regulation i load =0 to 10ma 30 mv input current sense section supply current i cc i load = 0a, v cc = 40v 12 30 a out1 input offset voltage v os1 0.4 2 mv out1 current accuracy i rg1 /i gs v sense = 100mv 2 5 % no-load out1 error v sense = 0v 0.1 1 a low-level out1 error v sense = 5mv 0.3 2 a shutdown supply current i cc ( shdn) v shdn = 3v 3 6 a shdn threshold voltage v th_shutd own (low ? high) 0.7 0.9 1.2 v shdn hysteresis 30 mv notes: 5) guaranteed by design.
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 6 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. typical performance characteristics v in =19v, c1=4.7 f, c2=22 f, l=4.7 h, rs1=110m ? , rs2=20m ? , real battery load, t a =25oc, unless otherwise noted. battery voltage(v) battery current(a) 2 cells battery charge curve 7.5 7.6 7.7 7.8 7.9 8 8.1 8.2 8.3 8.4 8.5 0 20 40 60 80 100 120 times(min) 0 0.5 1 1.5 2 2.5 v batt i batt 11 11.2 11.4 11.6 11.8 12 12.2 12.4 12.6 12.8 0 50 100 150 0 0.5 1 1.5 2 2.5 battery voltage(v) battery current(a) 3 cells battery charge curve effciency vs. i chg effciency vs. i chg times(min) v batt i batt charge current(a) battery voltage(v) 2 cells i chg vs. v batt curve 3 cells i chg vs. v batt curve 0 0.5 1 1.5 2 2.5 0246810 v in =12v v in =24v v in =19v 0 0.5 1 1.5 2 2.5 02468101214 battery voltage(v) charge current(a) charge current(a) v in =24v v in =19v batt float voltage vs. v in 8 8.1 8.2 8.3 8.4 8.5 8131823 28 v in (v) i chg (a) v batt (v) 2 cells battery 60.0 70.0 80.0 90.0 100.0 0 0.4 0.8 1.2 1.6 2 efficiency(%) i chg (a) efficiency(%) 2 cells battery v in =12v v in =15v v in =19v v in =24v 60.0 70.0 80.0 90.0 100.0 0 0.4 0.8 1.2 1.6 2 3 cells battery v in =15v v in =19v v in =24v batt voltage(v) batt float voltage vs. temperature 8 8.1 8.2 8.3 8.4 8.5 -20 0 20 40 60 80 temperature ( o c) 2 cells battery te mpe rature ( o c) charge current vs. temperature 1.2 1.4 1.6 1.8 2 2.2 -20 0 20 40 60 80 2 cells battery
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 7 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. typical performanc e characteristics (continued) v in =19v, c1=4.7 f, c2=22 f, l=4.7 h, rs1=110m ? , rs2=20m ? , real battery load, t a =25oc, unless otherwise noted. v in (v) efficiency vs. v in v batt =7.4v, i chg =2a 80 83 86 89 92 95 510152025 efficiency (%) i sys (a) i chg (a) current sharing 0 0.5 1 1.5 2 2.5 00.5 11.5 22.5 v in (v) ntc control window 0 0.5 1 1.5 2 2.5 3 81216202428 vntc(v) low temp off low temp on high temp on high temp off 2 cells battery
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 8 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. typical performanc e characteristics (continued) v in =19v, c1=4.7 f, c2=22 f, l=4.7 h, rs1=110m ? , rs2=20m ? , real battery load, t a =25oc, unless otherwise noted. trickle charge 2 cells, i chg = 2a, v batt = 5v cc charge 2 cells, i chg = 2a, v batt = 7.4v cv charge 2 cells, i chg = 2a, v batt = 8.4v power on 2 cells, i chg = 2a, v batt = 8v power off 2 cells, i chg = 2a, v batt = 8v en on 2 cells, i chg = 2a, v batt = 8v en off 2 cells, i chg = 2a, v batt = 8v ntc control 2 cells, i chg = 2a, v batt = 7.4v v acok 5v/div. v chgok 5v/div. v tmr 1v/div. i chg 2a/div. v in 10v/div. v batt 5v/div. v sw 10v/div. i batt 2a/div. v in 10v/div. v batt 5v/div. v sw 10v/div. i batt 2a/div. v in 10v/div. v batt 5v/div. v sw 10v/div. i batt 1a/div. v in 10v/div. v batt 5v/div. v sw 10v/div. i batt 500ma/div. v in 10v/div. v batt 5v/div. v sw 10v/div. i batt 200ma/div. v ntc 2v/div. v batt 5v/div. v sw 10v/div. i batt 2a/div. v en 5v/div. v batt 5v/div. v sw 10v/div. i batt 2a/div. v en 5v/div. v batt 5v/div. v sw 10v/div. i batt 2a/div. timer out 2 cells, i chg = 2a, v batt = 7.4v
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 9 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. typical performanc e characteristics (continued) v in =19v, c1=4.7 f, c2=22 f, l=4.7 h, rs1=110m ? , rs2=20m ? , real battery load, t a =25oc, unless otherwise noted. power path management_current sharing 2 cells, i chg = 2a, v batt = 7.4v power path management_steady state 2 cells, i chg = 2a, v batt = 8v, i sys =0.8a power path management_en on 2-cell, i chg =2a, v batt =7.6v, i sys =1a, v in =12v v en 5v/div. v batt 5v/div. v sys 5v/div. i sys 1a/div. i chg 1a/div. v en 5v/div. v batt 2v/div. v sys 10v/div. i sys 500ma/div. i chg 1a/div. v in 10v/div. v batt 5v/div. v sys 5v/div. i batt 1a/div. power path management_en off 2-cell, i chg =2a, v batt =7.6v, i sys =1a, v in =12v v in 10v/div. v batt 5v/div. v sys 5v/div. i batt 1a/div. v in 10v/div. i sys 500ma/div. i batt 1a/div. v sw 10v/div. v in 10v/div. i sys 1a/div. i batt 1a/div. v batt 5v/div.
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 10 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. pin functions pin # name description 1,6,10,12,22 nc no connection 2 ntc thermistor input. connect a resistor from this pin to the pin vref33 and the thermistor from this pin to ground. 3 acok valid input supply indicator. a logic low on this pin indicates the presence of a valid input supply. 4 chgok charging completion indicator. a logic lo w indicates charging oper ation. the pin will become an open drain once the charging is complete. 5 vref33 internal linear regulator 3.3v reference output. bypass to gnd with a 1 f ceramic capacitor. 7 en on/off control input. 8 shdn shutdown control of current sense amplif ier. connect to ground for normal operation. 9 rg1 gain resistor of current sense amplifier. 11, 21 gnd, exposed pad ground. this pin is the voltage reference for the regulated output voltage. for this reason care must be taken in its layout. this node should be placed outside of the d1 to c1 ground path to prevent switching current spikes from inducing voltage noise into the part. connect exposed pad to ground plane for optional thermal performance. 13 out1 output for driving resistor load. 14 rg2 gain resistor of current sense amplifier. 15 vcc power input of current sense amplifier. 16 compv vloop compensation. decouple this pin with a capacitor and a resistor. 17 cells command input for the number of li-ion cells. connect this pin to vref33 or keep it float for 3-cell operation or ground the pin for 2-cell operation. 18 compi iloop compensation. decouple this pin with a capacitor and a resistor. 19 batt positive battery terminal. 20 csp battery current sense positive input. connect a resistor rs1 between csp and batt. 23 tmr set time constant. 0.1ua charge and discharge the external cap. connect tmr pin to gnd to disable the internal timer. 24 bst bootstrap. this capacitor is needed to dr ive the power switch?s gate above the supply voltage. it is connected between sw and bst pins to form a floating supply across the power switch driver. 25, 26 sw switch output. 27 pin power supply voltage. the mp2619 operates from a +5.5v to +24v unregulated input. c1 is needed to prevent large voltage spikes from appearing at the input. 28 ain controller supply voltage.
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 11 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. operation the mp2619 is a peak current mode controlled switching charger for use with li-ion batteries. figure 1 shows the block diagram. at the beginning of a cycle, m1 is off. the comp voltage is higher than the current sense result from amplifier a1?s output and the pwm comparator?s output is low. the rising edge of the 600 khz clk signal sets the rs flip-flop. its output turns on m1 thus connecting the sw pin and inductor to the input supply. the increasing inductor current is sensed and amplified by the current sense amplifier a1. ramp compensation is summed to the output of a1 and compared to comp by the pwm comparator. when the sum of a1?s output and the slope compensation signal exceeds the comp voltage, the rs flip-flop is reset and m1 turns off. the external switching diode d1 then conducts the inductor current. if the sum of a1?s output and the slope compensation signal does not exceed the comp voltage, then the falling edge of the clk resets the flip-flop. the mp2619 have one internal linear regulators power internal circuit, vref33. the output of 3.3v reference voltage can also power external circuitry as long as the maximum current (30ma) is not exceeded. a 1uf bypass capacitor is required from vref33 to gnd to ensure stability. charge cycle (mode change: trickle ? cc ? cv) the battery current is sensed via rs1 (figure 1) and amplified by a2. the charge will start in ?trickle charging mode? (10% of the rs1 programmed current i cc ) until the battery voltage reaches 3.0v/cell. if the charge stays in the ?trickle charging mode? till ?timer out? condition triggered, and the charge is terminated. otherwise, the output of a2 is then regulated to the level set by rs1 . the charger is operating at ?constant current charging mode.? the duty cycle of the switcher is determined by the compi voltage that is regulated by the amplifier gmi. when the battery voltage reaches the ?constant voltage mode? threshold, the amplifier gmv will regulate the comp pin, and then the duty cycle. the charger will then operate in ?constant voltage mode.? automatic recharge after the battery has completely recharged, the charger disables all blocks except the battery voltage monitor to limit leakage current. if the battery voltage falls below 4.0v/cell, the chip will begin recharging using soft-start. the timer will then reset to avoid timer-related charging disruptions. charger status indication mp2619 has two open-drain status outputs: chgok and acok . the acok pin pulls low when an input voltage is greater than battery voltage 300mv and over the under voltage lockout threshold. chgok is used to indicate the status of the charge cycle. table 1 describes the status of the charge cycle based on the chgok and acok outputs. table 1 D charging status indication acok chgok charger status low low in charging low high end of charge, ntc fault, timer out, thermal shutdown, en disable high high pin ?v batt <0.3v. ain mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 12 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. when time-out occurs, charger is suspended. and only refresh the input power or en signal or auto-recharge (the event that v batt falls through 4v/cell) can restart the charge cycle. negative thermal coefficient (ntc) thermistor the mp2619 has a built-in ntc resistance window comparator, which allows mp2619 to sense the battery temperature via the thermistor packed internally in the battery pack to ensure a safe operating environment of the battery. a resistor with appropriate value should be connected from vref33 to ntc pin and the thermistor is connected from ntc pin to gnd. the voltage on ntc pin is determined by the resistor divider whose divide ratio depends on the battery temperature. when the voltage of pin ntc falls out of ntc window range, mp2619 will stop the charging. the charger will restart if the temperature goes back into ntc window range. power path management mp2619 can implement a switching charger circuit with power path management function, which realizes the current sharing of the charger and system load. in another word, mp2619 senses the system current and feeds it back, then reduces charge current according to the increase of the system current. however, after the charge current decrease to 0, the system current can only be limited by the adapter. the system current is satisfied first and always. it chooses the adapter as its power source when the adapter plugs in, and the battery is the backup power source when the adapter is removed. figure 2 to 6 shows the charge profile, operation waveform and flow chart, respectively.
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 13 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. block diagram charge control logic timer pre_regs 600khz osc vref ldo regulator drive a1 current sense ctrl charge current sense pwm comparator current limit comparator s r r q bst sw csp a2 batt 0.12v or 1.2v gmi gmv 3 bit trim 5 bit trim en nc vref33 ntc cells fb vbatt ctrl tmr 0.12v acok chgok fb fb gnd ain compi compv max trickle time max charge time max reflesh time acok sense amplifier rg2 rg1 vcc shdn out1 bias+ enable pin 1.2v 4v 2.8v ain batt+300mv tc/cc charge comparator recharge comparator bf comparator m1 comp x6 charge current sense iref rs1 l 2/3 cells battery cells figure 1 ? functional block diagram
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 14 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. charge profile and power path management function figure 2 ? li-ion battery charge profile i chg i sys power path management current sharing cc charge when i chg decreases to 0, the system current can only be limited by the adapter current capacity figure 3 ? power path management function- current sharing
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 15 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. operation flow chart figure 4? normal charging operation flow chart
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 16 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. operation flow chart (continued) figure 5? power path management operation flow chart
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 17 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. operation flow chart (continued) charge mode? v batt >v batt_tc v batt >v batt_full battery full? i chg =150 o c? tj<=130 o c? charge current thermal shutdown, acok& chgok are high fault protection yes charger recovery, return to normal operation yes no yes no yes no charge termination, acok& chgok are high yes ntc fault? no timer out ? no figure 6? fault protection flow chart
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 18 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. application information setting the charge current 1. standalone switching charger the charge current of mp2619 is set by the sense resistor rs1. the charge current programmable formula is as following: ?? ?? m ? rs1 200mv a i chg ? (1) 2. switching charger with power path management figure 7 shows the charge current sharing with the system current. figure 7? charge current sharing with system current the gain of the system current is set as: rg1 rgs1 gain ? (2) the voltage of out1 pin, v out1 can be calculated from: rg1 rgs1 rs2 i gain rs2 i v sys sys out1 ? ? ? ? ? ? (3) when the system current increased i sys , to satisfy the charge current decreased i sys accordingly. the relationship should be: rg1 rs1 rgs1 rs2 i rs1 v i sys out1 bat ? ? ? ? ? (4) because i sys = i batt , we can get: rg1 rgs1 rs2 rs1 ? (5) rgs1/2 causes the charge current sense error as it changes the sense gain of a2, which can be calculated from: ?? ?? ?? k ? rgs k ? 2 k ? 12.3 g a2 ? ? (6) the charge current is set as: ?? ?? m ? rs1 g 1230 a i a2 chg ? ? (7) then the influence of r gs1 to the charge current is: ?? ?? ?? m ? rs1 10 ? rgs 2000 a i chg ? ? ? (8) to decrease the power loss of the sensing circuit, choose rs2 as small as possible, 20m is recommended. too small r g1 results in too big current sense error of the system current, 50 ? is at least. substitute these two values into equation (5), then the calibrated charge current set formula in power path application is got from equation (8): ?? ?? ?? m ? rs1 10 m ? rs1 2.5 2000 a i chg ? ? ? ? (9) following table is the calculated rs1 and r gs1 value for setting different charge current. table2?i chg set in power path application i chg (a) r gs ( ? ) rs1(m ? ) 2 280 110 1.5 402 160 1 665 260 0.8 909 360 0.5 2k 800 if choose different rs2 and r g1 , re-calculated from equation (5) and equation (8), then get the different equation (9) and the table. also, any relationship between i sys and i batt can be realized by re-calculate equation (4), (5) and (8).
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger mp2619 rev. 1.01 www.monolithicpower.com 19 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. selecting the inductor a 1h to 10h inductor is recommended for most applications. the inductance value can be derived from the following equation. out in out in l osc v(vv) l vif ?? ? ?? ? (10) where i l is the inductor ripple current. v out is the 2/3 cell battery voltage. choose inductor current to be approximately 30% if the maximum charge current, 2a. the maximum inductor peak current is: ? ?? l l(max) chg i ii 2 (11) under light load conditions below 100ma, larger inductance is recommended for improved efficiency. for optimized efficiency, the inductor dc resistance is recommended to be less than 200m ? . ntc function as figure 8 shows, the low temperature threshold and high temperature threshold are preset internally via a resistive divider, which are 73%vref33 and 30%vref33. for a given ntc thermistor, we can select appropriate r3 and r6 to set the ntc window. in detail, for the thermistor (ncp18xh103) noted in above electrical characteristic, at 0oc, r ntc_cold = 27.445k; at 50oc, r ntc_hot = 4.1601k. assume that the ntc window is between 0oc and 50oc, the following equations could be derived: 73% vref33 v r6//r r3 r6//r th_low ntc_cold ntc_cold ? ? ? (12) 30% vref33 v r6//r r3 r6//r th_high ntc_hot ntc_hot ? ? ? (13) according to equation (12) and equation (13), we can find that r3 = 9.63k and r6 = 505k. to be simple in project, making r3=10k and r6 no connect will approximately meet the specification. figure 8? ntc function block selecting the input capacitor the input capacitor reduces the surge current drawn from the input and also the switching noise from the device. the input capacitor impedance at the switching frequency should be less than the input source impedance to prevent high frequency switching current passing to the input. ceramic capacitors with x5r or x7r dielectrics are highly recommended because of their low esr and small temperature coefficients. for most applications, a 4.7f capacitor is sufficient. selecting the output capacitor the output capacitor keeps output voltage ripple small and ensures regulation loop stability. the output capacitor impedance should be low at the switching frequency. ceramic capacitors with x5r or x7r dielectrics are recommended. pc board layout the high frequency and high current paths (gnd, in and sw) should be placed to the device with short, direct and wide traces. the input capacitor needs to be as close as possible to the in and gnd pins. the external feedback resistors should be placed next to the fb pin. keep the switching node sw short and away from the feedback network.
mp2619 ? 2a, 24v input, 600khz 2-3c ell switching li-ion battery charger notice: the information in this document is subject to change wi thout notice. please contact m ps for current specifications. users should warrant and guarantee that third party intellectual property rights ar e not infringed upon when integrating mps products into any application. mps will not assume any legal responsibility for any said applications. mp2619 rev. 1.01 www.monolithicpower.com 20 5/28/2015 mps proprietary information. patent protec ted. unauthorized photocopy and duplication prohibited. ? 2015 mps. all rights reserved. package information qfn28 (4mm x 5mm) side view top view 1 28 23 22 15 14 9 8 bottom view 3.90 4.10 2.50 2.80 4.90 5.10 3.50 3.80 0.50 bsc 0.18 0.30 0.80 1.00 0.00 0.05 0.20 ref pin 1 id marking 2.70 0.25 recommended land pattern 3.90 note: 1) all dimensions are in millimeters. 2) exposed paddle size do es not include mold flash. 3) lead coplanarity shall be 0.10 millimeter max. 4) drawing conforms to je dec mo-220, variation vhgd-3. 5) drawing is not to scale. pin 1 id see detail a pin 1 id option a 0.30x45 o typ. pin 1 id option b r0.25 typ. detail a pin 1 id index area 0.70 0.35 0.45 0.50 3.70 4.90

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