Application Note AN0020 Device: ICS1708 Description: Sequent

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Application Note AN0020 Device: ICS1708 Description: Sequent

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Application Note AN0020
Device: ICS1708
Description: Sequential Battery Charger NiCd/NiMH Battery Packs with Thermistors Theory Operation Cell, 2.7A-Hr NiMH /NiCd Battery Pack with Thermistors
Purpose schematic provided shows sequential charger configuration using ICS1708 NiMH/NiCd charge control with cost through-hole surface mount components available from many sources. Component count, size, cost reductions realized implementing through-hole surface mount transistors that include integral resistors available from semiconductor manufacturers such Semiconductor, ROHM, Panasonic. These sources also provide surface mount consisting multiple diodes, resistors, capacitors Charger Operation cost quad LM339 comparator cost ICS1708 charge control provide control charging battery pack alone either slot charging battery packs sequentially. Interfacing shown utilizing through-hole bipolar transistors, 2N3905 MPSA14 darlington, 1N4148 diodes. Under normal conditions fast charge begins automatically first battery pack detected. Once fast charge starts that battery pack, normally continues until fully charged ("ready"). Then charger proceeds fast charge other battery pack. Once fast charge starts battery pack, insertion removal other battery pack effect battery fast charging. Similarly fully charged battery pack that "ready" either slot affected insertion into removal battery pack condition other slot. Normal Priority Fast Charge Control Operation sections LM339 quad comparator slot used detecting battery insertion removal determining temperature status battery pack. Under normal conditions once fast charge begins, other slot disabled. ICS1708 that starts fast charge battery slot immediately removes supply from other ICS1708 using transistor interfacing. This action bi-directional between ICS1708s. there specified priority slot. Priority determined ICS1708 that starts fast charge first. When fast charge completes, ICS1708 indicates "ready" keeps supply using releases supply other ICS1708 turns transistor interfacing.
Rev:03/28/02
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Normal Battery Fast Charge Topping/ Maintenance Charge Stage Sequencing Fast charge starts first battery detected when normal condition battery packs charger power when battery pack inserted right after other. other slot disabled until fast charge completes first battery pack. Then fast charge begins immediately second battery pack. ICS1708 controlling slot with second battery pack disables topping charge first battery pack until fast charge completes second battery pack. This method provides full power availability fast charge uncharged battery pack also insures that interfering affects occur uncharged battery pack fast charges. When fast charge completes second battery pack, topping maintenance charging commences both battery packs. Once fast charge begins, topping charge capability other slot disabled. ICS1708 that controlling fast charge battery slot, immediately overrides function other ICS1708 using diode interfacing. This action bi-directional between ICS1708s. Topping Maintenance Charge Control Operation Once ICS1708 completes fast charge battery slot, battery ready use. battery remains slot, ICS1708 controlling that slot available apply topping maintenance charge stages. there battery other slot battery other slot cold fast charge (near colder), internal open, activated protector being most likely, topping charge proceeds "ready" battery. Other opens other battery pack such plus minus open open thermistor circuit allows topping continue charged battery that "ready" remains charging slot. Battery Management best remedy battery pack hotter) instruct user rest battery pack until cool touch. battery pack installed gets during fast charge other battery pack installed waiting fast charged, fast charge stops battery pack fast charge begins other battery. there other battery pack already completed fast charge (i.e. "ready"), fast charge fast stage remains active battery pack, charge current applied. battery indicator goes battery cools down degrees, battery indicator goes charging continues. Charge current applied removed appropriately into topping/maintenance charge stages. output lower LM339 comparator each slot goes when battery slot gets hot. comparator overrides function ICS1708 activates supply other ICS1708 diode interfacing. This action bi-directional between ICS1708s. battery indicator remains whenever battery pack temperature above Cold Battery Management best remedy cold battery pack (near colder) user allow battery pack warm above Cell manufacturers emphatic about fast charging very cold battery packs. Fast charging stops battery pack drops below this application. cold battery pack installed gets cold during charging process, other battery pack installed waiting fast charged, fast charge begins other battery. there other battery pack already completed fast charge i.e. "ready", cold battery must warm above before fast charge begins. charger slot with cold battery remains until battery warms above output upper LM339 comparator each slot goes high when battery slot gets cold. comparator removes supply ICS1708 controlling fast charge cold battery transistor interfacing. unlikely possible event battery gets cold while topping maintenance charge stages, comparator output high mentioned above bypassed diode interfacing supply ICS1708 remains topping/maintenance charges continue.
Rev:03/28/02
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Defective Battery Management
most common failure mode battery packs besides eventually losing their ability store charge shorted cells. Each these occurrences manifested users abrupt performance decline they observe knowledge they have about age, pattern, sometimes appearance battery pack. Galaxy Power provides methods detecting indicating shorted cells, this feature could also included part enhanced version this application. open overload use, open cell, interconnect, etc. plus minus path battery pack prevents charging that battery ICS1708 begins polling mode. other battery installed already been fast charged (i.e. "ready"), charger will fast charge that battery pack. open thermistor connection results same function open plus minus power path mentioned above, except ICS1708 does begin polling mode supplied with missing thermistor condition. Power Management application shown uses Power Integration's "top switch" converter typology create input power dual sequential charger. input voltage provided switch converter held 1.3V above voltage battery fast charging. This approach allows drop, cost linear current source configuration, minimizing heat generation. 2N3905 transistors connects switch voltage sense circuit appropriate battery; i.e. battery pack being fast charged. Using transistor interface ICS1708s switches IRF7321D2 FETKY which also controlled single current source control. channel transistor FETKY both switch drop linear current regulator pass element. current source control consists single 2N3905 transistor sensing voltage drop across .27, resistor with base emitter junction. 2N3905 collector controls gate FETKY transistor providing regulated 2.5A current source. Keeping charge current about 2.5A keeps charger's input power consumption just below 25Watts allowing Power Integration's cost TOP243 converter providing input power sequential charger. With 2.5A charging source battery packs charge from completely empty completely full well within ICS1708 (1Hour) minute fast charge timer limit.
1/18/02 Dave Whitmer Galaxy Power, Inc. Manager, Product Applications (whitmer@galaxypower.com)
Rev:03/28/02
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Rev:03/28/02
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Sequential Charger Electronic Component Costing
4.7K 910K 1N4148 2N3905 MPSA14 IRF7321D2 LM7805ACZ LM339 ICS1708 Zener 100pF .01uF .1uF Total
1/18/02
UNIT PRICE (1Kpcs) $0.01 $0.01 $0.01 $0.01 $0.01 $0.01 $0.01 $0.01 $0.01 $0.01 $0.01 $0.01 $0.01 $0.13 $0.04 $0.04 $0.06 $0.79 $0.14 $0.18 $0.73 $0.08 $0.10 $0.04 $0.03 $0.03
TOTAL $0.01 $0.02 $0.04 $0.04 $0.02 $0.10 $0.04 $0.06 $0.02 $0.06 $0.02 $0.02 $0.04 $0.13 $0.56 $0.28 $0.24 $1.58 $0.14 $0.18 $1.46 $0.48 $0.10 $0.07 $0.03 $0.06 $5.80
Component count cost reductions will realized surface mount (multiple transistors with integral resistors; multiple diode resistor networks) incorporated into approach. Contact Power Integrations TopSwitch control input pricing.
Rev:03/28/02
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Application Note AN0020 Device: ICS1708 Description: Sequent

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