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mp 2615 2a, 1 - or 2 - cell li - ion battery charger in 3mm x 3mm package mp 2615 rev. 1.0 www.monolith icpower.com 1 1/16/2014 mps proprietary information. patent protected. unauthorized photocopy and duplication prohibited. ? 2014 mps . all rights reserved. description the mp2615 is a high efficiency switch mode battery charger suitable for 1 - or 2 - cell l i thium - i on or l ithium - polymer applications. the mp2615 is capable of delivering 2a of charge current program mable via an accurate sense resistor over the en tire input range. the mp2615 regulates the charge current and full battery voltage using two control loops to achieve high accuracy constant current ( cc ) charge and constant voltage ( cv ) charge. c onstant - off - time (cot) mode control allows operation up to 99% duty cycle when the battery voltage is close to the input voltage and in order to keep charge current always at a relative high level. battery temperature and charging status are always monitored during each charging cycle. two status monitor output pins are provided to indicate the battery charging status and input power status. the mp2615 also features internal reverse blocking protection. the mp2615 is available in a 3mm 3mm 1 6 - pin qfn package . features ? 4 .75v to 18 v operating input voltage ? up t o 99% duty cycle operation ? up to 2a programmable charging current ? 0.75% full battery voltage accuracy ? 4.1v/cell and 4.2 v /cell s election for full battery voltage ? full integrated power switches ? internal loop compensation ? no external reverse blocking diode r equired ? preconditioning for fully depleted battery ? charging operation indicator ? programmable safety timer ? thermal shutdown protection ? cycle - by - cycle over current protection ? battery temperature monitor and protection applications ? smart phones ? portable hand - held solutions ? portable media players 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 r egistered t radem arks of monolithic power systems, inc. adam (analog digital adaptive modulation) and aam ( advanced asynchronous mode ) are t rademarks of monolithic power systems, inc. typical application l v i n c h g o k a c o k n t c e n a g n d b a t t c s p b s t s w m p 2 6 1 5 c 2 c 4 r 1 r 2 r 3 c t m r 1 - o r 2 - c e l l b a t t e r y r s 1 t m r v c c r n t c o f f o n s e l c e l l p g n d c 1 c 3 5 v t o 1 8 v i n p u t
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 2 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. ordering information part numb er* package top marking mp 2615gq qfn16 (3 3 mm) aeg * for tape & reel, add suffix C z ( e. g. mp 2615gq C z) ; package reference absolute maximum rat ings (1) v sw ................................ ............... C 0.3v to 2 3 v v in , v acok, v chgok ................................ ............. C 0.3v to 23 v v batt ,v csp .. . C 0.3v to 12 v v bst ................................ ..................... v sw + 6v all other pins ................................ .. C 0.3v to 6 v junction temperature .............................. 150 c lead temperature ................................ ... 260 c continuous power dissipation (t a = + 25 c) (2) ................................ ............................ 2.5 w operating temperature ............. C 4 0 c to +85 c recommended operating conditions ( 3 ) v in ................................ ................. 4. 7 5 v to 18v v batt ................................ ................. 2 v to 8.4 v operating junction temp . (t j ). C 40 c to +125 c thermal resistance ( 4 ) ja jc qfn16 (3x3mm) .................... 50 ...... 12 ... c/w notes: 1) exceeding these ratings may damage the device. 2) the maximum allowable power dissipation is a function of the maximum junction temperat ure t j (max), t he 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 power 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. 1 2 3 4 5 6 7 8 1 1 1 0 9 1 6 1 5 1 4 1 3 1 2 n t c t m r a c o k p g n d b s t b a t t c h g o k c s p v i n v c c s w a g n d n / c e n c e l l s e l
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 3 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. electrical character istics v in = 12 v, v cell = 0 v, v s el = 0 v , c1 = 22 f, c2=22 f, t a = 25 c, unless otherwise noted. parameter symbol condition min typ max units input voltage and current input voltage v in v cell = 4v 4.5 5 18 v v cell = 0v 8.75 12 18 under voltage lockout threshold rising v u vlo 3 .55 3.75 3.95 v under voltage lockout threshold hysteresis 225 mv supply current i shdn = 4v , shutdown current 0. 27 ma i q = 0 v , quiescent current 1.1 power mos high - side switch on resistance r h_ ds(on) measured from vin to sw 1 1 0 m low - side switch on resistance r l_ ds(on) 1 1 0 m switch leakage = 4v, v sw = 0v 0 1 a frequency and time parameter switching frequency f sw v batt = 7.5 v 760 k hz fold - back frequency v batt = 0v 1 60 k hz minimum o ff time ( 5 ) t o ff v batt = 9 v 2 00 ns charging parameter terminal battery voltage v batt _full v sel = 0v 4 . 168 4.2 4.231 v /cell v sel = 4v 4.069 4.1 4.131 battery over voltage threshold v b ovp v c el l = 0v , v s el =0v 8.34 8.71 9.08 v c e l l = 0 v , v s el =4v 8.14 8.51 8.88 v c e l l = 4 v , v s el =0v 4.17 4.36 4.54 v c el l = 4v , v s el = 4 v 4.07 4.26 4.44 recharge t hreshold at v batt v rech v sel = 0v 4 .0 v sel = 4v 3.9 recharge hysteresis 1 50 mv /cell trickle c harge v oltage t hreshold v tc v sel = 0v 3 v /cell v sel = 4v 2. 91 trickle c harge h ysteresis 225 mv /cell peak current limit cc 3. 2 a t rickle 2.2 cc c urrent i cc rs1 = 50 m 1.8 2 2.2 a trickle c harge c urrent i t c 5% 10 % 15% i cc en en
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 4 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. electrical character istics ( continued ) v in = 12 v, v cell = 0 v , v s el = 0 v , c1 = 22 f, c2=22 f, t a = 25 c, unless otherwise noted. parameter symbol condition min typ max units termination c urrent t hreshold i bf 5% 10% 15% i cc v in min imum h ead - room (reverse blocking) v in ? v batt 300 mv maximum c urrent sense volta ge (csp to batt) v sense 90 100 11 0 mv csp, batt current i csp , i batt charging disabled 3 a acok/chgok open - drain s ink c urrent v drain = 0.3v 5 ma vcc regulator output vcc output voltage v cc 4. 3 5 4. 5 4. 65 v vcc load regulation ? v cc i load =0 to 10m a 10 mv en control input low voltage 0.4 v input high voltage 1.8 v input current i en = 4v 4 a = 0v 0.2 timer pr otection trickle charge time t trickle_tmr c tmr = 0. 47 f 30 m in s cc/cv charge time t total_tmr c tmr = 0. 47 f 1 65 ntc protection ntc low temp rising threshold r ntc = ncp18x103 , 0c 7 2 73. 3 7 4.6 %v cc ntc low temp rising threshold hysteresis 2 n tc high temp falling threshold r ntc = ncp18x103, 50c 2 8 29. 3 3 0.6 ntc low temp fall ing threshold hysteresis 2 thermal protection thermal shutdown ( 5 ) t shdn 150 c thermal s hutdown h ysteresis ( 5 ) 2 0 c reverse leakage blocking battery reve rse leakage current i leakage v c e l l = 0v 3 ua v c el l = 4 v 0.5 a notes: 5) guaranteed by design. en
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 5 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. pin functions package pin # name description 1 sw switch output 2 vin power supply voltage. 3 vcc coarse regulator output. internally generated 4.5 v. bypass with a 1f capacitor to a gnd. used to be low - side switch driver and pull - up bias voltage ntc resistive divider. do not connect any external load at this pin. 4 cell command input for the number of li - ion cells. connect this pin to vcc for 1 - c ell ap plication and short it to agnd or keep it float ing for 2 - cell application. 5 sel i nput pin for setting terminal battery voltage: sel = low - level or float : v batt = 4.2v/cell. sel = high - level: v batt =4.1v/cell. 6 on/ off control input. t his pin is pulled to gnd with a 1meg internal resistor. 7 n/c n o connect. please leave this pin floating. 8 agnd analog ground. 9 batt positive battery terminal. 10 csp battery current sense positive input. connect a resistor r s1 between csp a nd batt. 11 charging completion indicator. a logic low indicates charging operation. the pin will become an open drain once the charge is complete d or suspended. 1 2 valid input supply indicator. a logic low on this pin indicates the presence of a valid input power supply. 13 ntc thermistor input. connect a resistor from this pin to the pin vcc and the t hermistor from this pin to ground. 14 tmr internal safety timer control. connect a capacitor from this no de to agnd to set the timer. and the timer can be disabled by connecting this pin to agnd directly. 15 bst bootstrap pin . a capacitor is needed to drive the power switchs gate above the supply voltage. it is connected between sw and bs t pins to form a f loating supply across the power switch driver. 16 p gnd power ground. en chgok acok
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 6 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. typical performance characteristics v in = 5 v /9v , c1=c2=22 f, sel=float/high, cell=float/high, l=6.8 h, rs1=50m , battery simulator, t a = 25 c, unless otherwise noted.
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 7 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. typical perfo rmance characteristi cs (continued) v in = 5 v /9v , c1=c2=22 f, sel=float/high, cell=float/high, l=6.8 h, rs1=50m , battery simulator, t a = 25 c, unless otherwise noted.
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 8 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. typical performance characteristics (continued) v in = 5 v /9v , c1=c2=22 f, sel=float/high , cell=float/high, l=6.8 h, rs1=50m , battery simulator, t a = 25 c, unless otherwise noted.
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 9 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. typical performance characteristics (continued) v in = 5 v /9v , c1=c2=22 f, sel=float/high, cell=float/high, l=6.8 h, rs1=50m , battery simulator, t a = 25 c, unless otherwise noted.
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 10 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. typical performance characteristics (continued) v in = 5 v /9v , c1=c2=22 f, sel=float/high, cell=float/high, l=6.8 h, rs1=50m , battery simulator, t a = 25 c, unless otherwise noted.
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 11 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. functional block dia gram figure 1 : functional block diagram c h a r g e c o n t r o l l o g i c t i m e r p r e _ r e g s o s c v r e f l d o r e g u l a t o r d r i v e a 1 c u r r e n t s e n s e c t r l c h a r g e c u r r e n t s e n s e p w m c o m p a r a t o r c u r r e n t l i m i t c o m p a r a t o r s r r q b s t s w c s p a 2 b a t t 0 . 1 2 3 v o r 1 . 2 3 v g m i g m v 5 b i t t r i m e n v c c n t c c e l l s f b b a t t c t r l t m r o v p a c o k c h g o k f b f b a g n d v i n 1 . 2 3 v 1 . 1 7 1 v 0 . 8 7 9 v v b a t t + 0 . 2 v t c / c c c h a r g e c o m p a r a t o r r e c h a r g e c o m p a r a t o r o v p c o m p a r a t o r m 1 c o m p 1 . 2 3 v r s 1 l 1 - o r 2 - c e l l b a t t e r y c e l l s m 2 m 3 o v p i c h g i h s a c o k c o m p a r a t o r v i n s e l i c h g 0 . 1 2 3 v b f c o m p a r a t o r p g n d c o m p i c o m p v
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 12 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. operation the mp2615 is a peak current mode controlled switching charger for 1 - or 2 - cell l i thium - i on and lithium - polymer batter y . the mp2615 int egrates both the high - side and low - side switches of the synchronous buck converter to provide high efficiency and save on pcb area. charge cycle (mode change: tc ? ? the mp261 5 regulates the charge current (i chg ) and battery voltage (v batt ) using two control loops to achieve high ly - accura te constant current ( cc ) charge and constant voltage ( cv ) charge. as shown in figure 2 , when the v batt < v tc , t he mp2615 st ays in trickle - charg e mode and the output of charge current loop compi dominates the control. the battery is charged by a trickle - charge current i tc until the battery voltage reaches v tc . if the charg er stays in the trickle - charg e mode ti l l the trickle - charge timer is triggered , charging will be terminated. t h e mp2615 will enter c onstant - current c harg e mode once the battery voltage rises higher than v tc . in this mode the charge current will increase from i tc to i cc to fast charge the battery . when the battery voltage rises over full battery voltage v batt_full , the charger enters into constant - volt age mode. in constant voltage mode, the battery voltage is regulated at v batt_full precisely and the charge current will fall naturally due to the existing equivalent internal resistance of the battery. for the operation flow chart, please also refer to fi gure 4. figure 2 : li - ion battery charge profil e c c c h a r g e t h r e s h o l d c v c h a r g e t h r e s h o l d c c c h a r g e i c h g v b a t t c h a r g e f u l l t c c h a r g e c u r r e n t c c c h a r g e c u r r e n t c v c h a r g e a u t o - r e c h a r g e a u t o - r e c h a r g e t h r e s h o l d i b f t r i c k l e c h a r g e
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 13 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. charge full termination and au to - recharge when the charg e current drops below the termination threshold (i bf ) during the cv charge phase , the charger will stop charging and the pin becomes open drain. the timer will also be reset and turned off. once the batte ry voltage decreases below the recharge threshold v rech ( 4.0v /cell while connect sel - pin to agnd) , recharg ing will automa tically kick in and the timer restarts a new charge cycle. cot charge mode the mp2615 uses the floating ground method to drive the high - side mosfet of the buck converter. during the off - time of the high - side mosfet, the bst capacitor is recharged and the v oltage across it is used as the hs - mos gate drive. thus a minimum off - time 200ns is required to maintain sufficient voltage at bst capacitor. when 200ns minimum off - time is achieved due to large duty cycle, the mp2615 will enter cot (constant off - time) char ge mode. in this mode of operation, switching frequency is slightly decreased in order to achieve 99% duty cycle. charg e statu s indication the mp2615 ha s two open - drain status outputs, pin and pin . t he pin goes low when the input vo ltage is 3 00mv larger than battery voltage and over the under voltage lockout threshold . pin is used to indicate the status of the charge cycle. t able 1 summarized the operation of b oth and according to the status of charge . table 1 : charging status indication charger s tatus l ow l ow in c harging l ow hi gh impedance e nd of c harge ; ntc fault; timer out: di sable ; t hermal s hutdown ; hi gh impedance hi gh impedance v in a bsent ; v in ? v batt < 0. 3 v safety timer operation the mp 2615 has an internal safety timer to terminate charg ing during time out. the capacitor c tmr connected between the tmr pin and gnd is used to set the internal oscillator period , ( 1 ) this timer limit s the max trickle charge time to 8192 i nternal oscillating periods . if the charger stays in trickle charge mode for longer than t he max oscillating periods, it will be terminated and the become s open drain to indicate the timer - out fault. if charge cycle successfully goes through trickle charge within the allowed time limit, it enters into the cc charge mode and the timer co ntinues to count the oscillating periods . when the battery is charged full, the timer turns off and clears the counter, waiting for the auto - recharge to restart. if the charge time during cc/cv mode exceeds 49152 oscillating periods and the battery full has not been qualified, the charger will be terminated and a timer - out fault is also indicated by floating the . the charger can exit the timer - out fault state and the on - chip safety timer re start s count ing when one of the following conditions occurs: ? the batte ry voltage falls below the auto - recharge threshold v rech . ? a power - on - reset (por) event occurs ; ? pin is toggled . the timer can be disabled by pulling tmr - pin to agnd. t hus, t he trickle mode ch arge time is: ( 2 ) if connect a c tmr of 0. 47uf , the trickle charge time is about 30 minutes. the cc/cv mode charge ti me is: ( 3 ) if connect a c tmr of 0. 47uf , the cc/cv charge time is 2.95 hours. chgok acok acok acok acok en p tmr t (seconds) 0.46 c (uf) ?? trickle_tmr tmr t (minutes) 62.8 c (uf) ?? total_tmr tmr t (hours) 6.28 c (uf) ??
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 14 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. negative thermal coefficient (ntc) ther mistor the ntc pin allows the mp2615 to sense the battery temperature using the negative thermal coefficient (ntc) resistor available in the battery pack to ensure safe operating environment of the battery. . a resistor with appropriate value should be con nected from vcc to ntc pin and the thermistor is connected from ntc pin to agnd. the voltage on the ntc - pin is determined by the resistor divider whose divide - ratio depends on the battery temperature. when the voltage at the nt c pin falls out of the ntc wi ndow range, the charging will pause until the battery temperature goes back to normal operating conditions. as a result the mp2615 will stop charging and report this condition to the status pins. charging will automatically resume after the temperature fa lls back within safe range. short circuit protection the mp26 15 has an internal comparator to check for battery short circuit . once v batt falls below 2v , the device detects a battery - short status and the cycle - by - cycle peak current limit falls to about 2. 2a to limit the current spike during the battery - short transition. furtherm ore, the switching frequency also fold s back to minimize the power loss. thermal shutdown protection to prevent the chip from overheating during charging, the mp26 15 monitors the ju nction temperature, t j , of the die. once t j reaches the thermal shutdown threshold (t shtdwn ) of 150c, the charger converter turns off. once the t j falls below 130 c the c harging will restart .
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 15 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. input power up start up timing flow figure 3 : input power s tart - up timing diagram
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 16 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. operation flow chart figure 4 : operation f l ow chart
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 17 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. application informat ion component selection charge current setting the constant charge current (i cc ) of the mp2615 can be set by the sense resistor rs1 (see typical application). the equation to determine the programmable cc - charge current is expressed as follow ing , ( 4 ) to get 2a i cc , a rs1 of 50m ? should be selected. accordingly, t he trickle charge current (i tc ) can be obtained by the following equation , ( 5 ) in ductor selection to select the right inductor , a trade off should be made between cost, size, and efficiency. a n inductor of lower inductance value correspond s with smaller size, but it result s in higher ripple currents , higher magnetic hysteretic losses, and higher output capacitance s . conversely , higher inductance value is beneficial to getting a lower ripple current and smaller output filter capacitors, but result ing in higher inductor dc resistance (dcr) loss. based on practical experience , the inductor ripple current should not exceed 30 % of the maximum charge current under worst cases . for the mp261 5 with a typical 12 v input voltage to charge a 2 - cell battery , the maximum inductor current ripple occurs at the corner point between trickle charge and cc charge (v batt = 6 v). inductance estimations are as follow: (6) w here v in , v batt , and f s are the typical input voltage, the cc charge threshold , and the switchi ng frequency , respectively. and is the maximum i nductor ripple current , which is usually 30% of the cc charge current . (7) based on the condition where i cc = 2a, v in = 12 v, v batt = 6 v and f s = 760 k hz the calculated inductance is 6.6 h. the inductor saturation current must exceed 2.6a at least and have some tolerance . to optimize efficiency, chose an inductor with a dc resistance less than 5 0m? . ntc resistor divider selection figure shows that an internal resistor divider is used to set the low temperature threshold and high temperature threshold at 7 3. 3 % vcc and 29. 3 % v cc , respectively . for a given ntc , t hermistor, select appropriate r t1 and r t2 to set the ntc window. figure 5 : ntc function block the thermistor ( ncp18xh103 ) noted above has the following electrical characteristic: ? at 0 c, r ntc_cold = 27.445k ? ; ? at 50 c, r ntc_hot = 4.1601k ? . the following equations are derived assuming that the ntc window is between 0 c and 50 c: (8) (9) according to e quation (8) (9) , and the required battery temperature range to calculate r t1 and r t2 . cc 100mv i (a) rs1(m ) ? ? (a) ) rs1(m 10mv 10%i i cc tc ? ? ? s in batt l_max batt in f v v i v - v l ? ? l_max i cc l_max 30%i i ? ntc v cc low temp threshold high temp threshold r ntc r t 1 r t 2 v th _ low v th _ high 73.3% = vref33 v = //r r + r //r r th_low ntc_cold t2 t1 ntc_cold t2 29.3% = vref33 v = //r r + r //r r th_high ntc_hot t2 t1 ntc_hot t2
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 18 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. input capacitor selection the i nput capacitors c1 from the t ypical a pplication circuit absorbs the maximum ripple current from the buck converter, which is given by: (10) for a given i c c = 2 a, v t c = 6 v, v in_max = 1 8 v, the maximum ripple current is 1 a. select the input capacitors so that the temperature rise due to the ripple current does not exceed 10c. use ceramic capacitors with x5r or x7r dielectrics because of their low esr and small temperature coefficients. for most applications, use a 22 f ca pacitor. output capacitor selection the output capacitor c2 (see the t ypical a pplication circuit ) is in parallel with the battery . c 2 absorbs the high - frequency switching ripple current and smoothes the output voltage. its impedance must be much less than that of the battery to ensure it absorbs the ripple current. use a ceramic capacitor because it has lower esr and smaller size . . t he output voltage ripple is given by , (11) in order to guarantee 0.5% full battery voltage accuracy, the maximum output voltage ripple must not exceed 0.5% (e.g. , 0.1%). the maximum output voltage ripple occurs at the minimum battery voltage of the cc charge and the maximum input voltage. for v in_max = 1 8 v, v cc_min = v t c = 6 v, l = 6.8 h, f s = 760k hz , ? r o_max = 0.1% , the output capacitor can be calculated as , (12) we can then approximate this value and cho o se a 22f ceramic capacitor . pcb layout guide pcb layout is important to meet specified noise, efficiency and stability req uirements. the following design considerations can improve circuit performance , 1) route the power stage adjacent to the grounds. aim to minimize the high - side switching node (sw, inductor), trace lengths in the high - current paths and the current - sense resist or trace. k eep the switching node short and away from the feedback network . 2) connect the charge current sense resistor to csp (pin 10 ), batt (pin 9 ) . minimize the length and area of this circuit loop. 3) place the input capacitor as close as possible to the v in and p gnd pins. place the output inductor close to the ic as and connect the output capacitor between the inductor and pgnd of the ic. this minimizes the current path loop area from the sw pin through the lc filter and back to the pgnd pin. 4) connect agnd and pgnd at a single point. 5) figure 6 is a pcb layout reference design. in_max tc in_max tc cc rms_max v ) v (v v i i ? ? l f 8c v v 1- v v r 2 s o in o o o o ? ? ? tc in_max o 2 s o_max v 1- v c 21.3 f 8f l r ? ? ? ?
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 19 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. figure 6: mp2615 pcb guild design a g n d p g n d b s t t m r n t c a c o k c e l l s e l e n n c s w v i n v c c c h g o k c s p b a t t g n d g n d v i n b a t t
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger mp 2615 rev. 1.0 www.monolithicpower.com 20 1/16/2014 mps proprietary information. patent protected. unauthorized photo copy and duplication prohibited. ? 2014 mps . all rights reserved. typical application circuits figure 7 : typical application circuit to charge a 2 cell battery with 12v in . l v i n c h g o k a c o k n t c e n a g n d b a t t c s p b s t s w m p 2 6 1 5 c 2 c 4 r 1 r 2 r 3 c t m r 2 c e l l b a t t e r y r s 1 t m r v c c r n t c o f f o n s e l c e l l p g n d c 1 c 3 1 u f 1 u f 1 0 0 n f 2 2 u f 1 0 k 1 0 k 1 k 1 k 6 . 8 u h 5 0 m v i n 2 2 u f
mp 2615 C 2a, 1 - cell or 2 - cell li - ion bat tery charger notice: the information in this document is subject to change without notice. please contact mps for current specifications. users should warrant and guarantee that third party i ntellectual p roperty r ights are not infringed upon when integrating mps produc ts into any application. mps will not assume any legal responsibility for any said applications. mp 2615 rev. 1.0 www.monolithicpower.com 21 1/16/2014 mps proprietary information. patent protected. unauthorized photocopy and duplication prohibited. ? 2014 mps . all rights reserved. package i nformation qfn16 3x3 p a c k a g e o u t l i n e d r a w i n g f o r 1 6 l f c q f n ( 3 x 3 m m ) m f - p o - d - 0 1 5 7 r e v i s i o n 0 . 0 s i d e v i e w b o t t o m v i e w n o t e : 1 ) a l l d i m e n s i o n s a r e i n m i l l i m e t e r s . 2 ) e x p o s e d p a d d l e s i z e d o e s n o t i n c l u d e m o l d f l a s h . 3 ) l e a d c o p l a n a r i t y s h a l l b e 0 . 1 0 m i l l i m e t e r s m a x . 4 ) j e d e c r e f e r e n c e i s m o - 2 2 0 . 5 ) d r a w i n g i s n o t t o s c a l e . p i n 1 i d m a r k i n g t o p v i e w p i n 1 i d i n d e x a r e a r e c o m m e n d e d l a n d p a t t e r n p i n 1 i d 0 . 1 0 x 4 5 t y p . 0 . 1 0 x 4 5

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