[AK7903] ms1190e00 1 2010/6 general description AK7903 is a dcdc step-down converter with fixed cur rent control type for nih2 battery. this device detects external resistor current, and controls swi tching regulator output voltage with fixed current. AK7903 can convert the battery voltage with a built -in general-purpose amplifier, so cpu can monitor battery easily. AK7903 also built-in output voltage detection function (external resistors fail detect ion), output short protection function, thermal protectio n circuit, so it can work safely with few radiant h eat. AK7903 is the most suitable charger device for port able system which uses nih2 battery. the AK7903 is available in qfn package (3.0mm x 3.0mm), utilizing less board space than competitive offerings. feature most suitable charger device for nih2 battery charg ing switching dcdc converter with fixed current contr ol circuit power supply voltage: 4.1v 5.5v output voltage: 0.2v 3.6v maximum charger current (pin control available): 0.4a @ iset= low (sense resistor= 0.353) 0.3a @ iset= low (sense resistor= 0.470) 80ma @ iset= high (sense resistor= 0.470) charger current accuracy: 5% low power consumption: 2ua @ shutdown switching frequency: external resistor adjustable ( < 10%) high efficiency: >80% @vin=5v, vout= 1.8v, iout= 0. 3a generalpurpose amplifier builtin input selectable (switch builtin) protection function (auto recovery) over current protection circuit thermal protection circuit: 120 (recovery at 100 ) ta: 30 70 few external parts needed: power mosfet builtin small size package: 16pins qfn (3mm3mm, 0.5mm pitc h) application: system which used 1 or 2 series nih2 b attery dcdc stepdown converter for nih2 battery ak 7903
[AK7903] ms1190e00 2 2010/6 block diagram figure 1. AK7903 block diagram *) the bulk of pmos connects to the high voltage o f vin or sw. battery pack pwm control sense res sense vin iset en1 fb gnd sw l=4.7 h co= 10 f ci=1 f comp tsd current limit opout en2 pin1 gain=3.75 times vdd AK7903 pin2(gain=1.96 times) nin rt cont current monitor ci=0.1 f sw1 sw2 bulk sw3
[AK7903] ms1190e00 3 2010/6 pin layout 13 cont top view 15 16 8 7 6 5 en2 vdd opout vin sw gnd iset 12 sense 11 10 9 1 2 3 4 fb comp rt nin pin2 pin1 en1 14 pin / function no. pin name i/o protection diode function 1 nin i opamp negative input pin 1 2 pin2 i opamp positive input pin 2 3 pin1 i opamp positive input pin 1 4 en1 i enable pin 1 5 iset i charge current setting pin 6 gnd ground pin 5 bulk gnd 4 bulk gnd 3 bulk gnd 2 bulk gnd 1 vdd gnd
[AK7903] ms1190e00 4 2010/6 pin name i/o protection diode function sw o choke coil connection pin vin dcdc power supply pin rt o frequency setting pin (adjusted by external resistor) comp o boost compensation pin fb i output voltage detection pin sense i connect to current detection sense resistor cont i pin1 or pin2 select pin (pin1@cont= l, pin2 @cont= h) en2 i opamp enable pin vdd opamp power supply pin opout o opamp output pin 16 vdd gnd 14 vdd gnd 13 vdd gnd 12 bulk gnd 11 bulk gnd 10 vin gnd 9 vin gnd 7 bulk gnd
[AK7903] ms1190e00 5 2010/6 absolute maximum rating (gnd=0v; (note 1)) parameter symbol min max units vin pin voltage vin ? 0.3 6.5 v input current (fb, sense, cont, en1, en2, iset, rt, comp) iin 10 ma sw mos. peak current ici 1.0 a junction temperature tj 125 storage temperature tstg ? 40 125 power dissipationnote 2 pd 1700 w note 1. all voltage is respect to ground. note 2. in case that pcb(size: 76 114mm,1.6mm, 4 layer) , material is fr4, base on jd ec517, and temperature is 25 , windless. note: operation at or beyond these limits may resul t in permanent damage to the device. normal operation is not guaranteed at these ex tremes. recommended operating conditions (gnd=0v; (note 1)) parameter symbol min typ max units power supply for dcdc vin 4.1 5.5 v power supply for opamp vdd 2.8 3.2 v ambient temperature top ? 30 25 70 * akm assumes no responsibility for the usage beyon d the conditions in this datasheet.
[AK7903] ms1190e00 6 2010/6 analog characteristics (ta=25 , vin=5.0v, vdd=3.0v, gnd=0v( note 3)) symbol parameter condition min typ max unit dcdc converter fixed current circuit vin input voltage in the case of vin=3.8v, vout= 1.8v is guaranteed 4.1 (3.8v) 5.5 v iddsdn shutdown current en=l 2 10 ua treg stop temperature 120 ilimt current limit vin=5.0v 1000 ma vsense current detection accuracy r=0.47,iout=300ma 5 5 ipre1 output current1 r=0.353, iset= low vin=4.1 5.5v,vout=0.2 3.5v 400 ma ipre2 output current 2 r=0.470, iset= low vin=4.1 5.5v,vout=0.2 3.5v 300 ma ipre3 output current 3 r=0.470, iset= high vin=4.1 5.5v,vout=0.2 3.5v 80 ma fosc switching frequency freq= 1220khz 2 +2 % tstart startup time the time which from en lh to the time which charge current is 90% of the setting current. 20 ms effi efficiency (note 4) vout=1.8v iout=300ma 80 opamp vdd input voltage 2.8 3.2 v maximum output load R 10k 1/2*vdd 0.05 vdd0.05 v gain1 gain 1 pin1opout 3.75 gain2 gain 2 pin2opout 1.96 opout1 output level 1 pin1= 1.75v 1.95 v opout2 output level 2 pin2= 3.5v 2.26 v idd1 power consumption 1 en2= h, o? 1.7 4 ma idd2 power consumption 2 en2= l, o? 0.1 2 a load cap maximum load cap 50 pf digital input/output vil low level input input pins 0.4 v vih high level input input pins 1.2 v vimax maximum input en2, cont pins vdd+0.3 v ibias1 input bias current 1 en1 pin =vin 5 a ibias input bias current 2 input pins 1 ua note 3. all the characteristic is supposed that rec ommend external parts is used. note 4. exclude sense resistor consumption.
[AK7903] ms1190e00 7 2010/6 operation overview input and output AK7903 is a dcdc converter which power mosfet is bu iltin, and input voltage support 4.1v 5.5v; the device is the most suitable charger for nih2 battery system w hich used 1 or 2 series nih2 battery. in the case o f charging to 1 cell, the characteristic can be guaranteed even inp ut voltage below 3.8v. AK7903 detects external resi ster current through fb and sense pins, and it regulates switchi ng regulator output voltage in order to maintain dc dc output current fixed. when the sense resistor current decr eased, dcdc output voltage will be increased, so ou tput current increase with coil current limitation (1.0a @typ). sense resistor is recommended less than 0.353 . use small size sense resistor, the charge current is possible not reach set current. protection functions AK7903 is builtin over current protection circuit and thermal protection circuit for preventing devic e be damaged. protection condition and recovery method is showed at table 1. protection function working condition device condition recovery condition current limit (including output short to ground) coil current 1.0a pmos= off in the case that coil current > 1.0a. it will be judged at every cycle. auto recovery when left condition is cancelled. thermal shutdown chip temperature exceed 120 (typ) switching stop auto recovery when chip temperature below 100 (typ). table 1. protection function output pmos bulk control AK7903 controls output pmos bulk, so is the most su itable construction for system environment. gain switching for opamp table 2 shows opamp gain setting. en2 cont sw1 sw2 sw3 ? 0 0 or 1 off off off powerdown 1 0 on off on gain=3.75 times 1 1 off on on gain=1.96 times table 2. opamp gain setting
[AK7903] ms1190e00 8 2010/6 system design and recommended parts figure 2. ??A recommend parts : component symbol value type dimensions supplier capacitance ci 4.7uf c1608jb1e105k 1608 type (25v) tdk inductance l 4.7uh ltf5022 5.0 5.2 2.2 tdk capacitance co 10uf c2012jb1c106k 2012 type tdk *) excellent dc bias characteristic of ci is recomm ended. low value of ci is possible to effect stability o f AK7903. battery pack pwm control sense res sense vin iset en1 fb gnd sw l=4.7 h co= 10 f ci=1 f comp tsd current limit opout en2 pin1 gain=3.75 times vdd AK7903 pin2(gain=1.96 times) nin rt cont current monitor ci=0.1 f sw1 sw2 bulk sw3
[AK7903] ms1190e00 9 2010/6 package (a) package information uqfn 16pin unit mm 3.00 0.05 3.00 0.05 1.8 0.05 0.575 0.05 0.25 0.05 0.05 m 1.25 0.05 exposed pad 0.05 s 0. 58+0.02 0.58-0.03 d 1 4 5 8 9 12 13 1 6 c0.05 ) please connect exposed pad to ground 0.50 0.10 0.05 0.30 0.05 figure 3 package information (b)recommend food pattern p=0.50 3.50 3.50 1.80 1 16 1.25 0.55 0.2 5 figure 4. recommend food pattern
[AK7903] ms1190e00 10 2010/ 6 marking 7903 ywwa market no. product no. data code pin #1 indication ywwa: date code (4 digit) y product year (a.d.) last no(ex. 2009 9 ww product week a product manage code revision history date (yy/mm/dd) revision reason page contents 10/06/03 00 first edition important notice these products and their specifications are subject to change without notice. when you consider any use or application of these p roducts, please make inquiries the sales office of asahi kasei emd corporation (akemd) or authorized distributors as to current status of the products. akemd assumes no liability for infringement of any patent, intellectual property, or other rights in t he application or use of any information contained herein. any export of these products, or devices or systems containing them, may require an export license or other official approval under the law and regulations of the count ry of export pertaining to customs and tariffs, cur rency exchange, or strategic materials. akemd products are neither intended nor authorized for use as critical components note1) in any safety, life support, or other hazard related device or system note2) , and akemd assumes no responsibility for such use, except for the use approved with the express written consent by re presentative director of akemd. as used here: note1) a critical component is one whose failure to function or perform may reasonably be expected to result, whether directly or indirectly, in the loss of the safety or effectiveness of the device or system con taining it, and which must therefore meet very high standards o f performance and reliability. note2) a hazard related device or system is one des igned or intended for life support or maintenance o f safety or for applications in medicine, aerospace, nuclear energy, or other fields, in which its failure to f unction or perform may reasonably be expected to result in los s of life or in significant injury or damage to per son or property. it is the responsibility of the buyer or distributo r of akemd products, who distributes, disposes of, or otherwise places the product with a third party, to notify su ch third party in advance of the above content and conditions, and the buyer or distributor agrees to assume any and a ll responsibility and liability for and hold akemd harmless from any and all claims arising from the use of said pro duct in the absence of such notification.
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