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SS4035G

1/09/2006 Rev.3.01

Two-Cell Li-Ion and Li-Polymer Charge Management IC

Charge management for two-cell Li-Ion or Li-Polymer battery packs

Individual cell monitoring - avoids over-charging

Pin-selectable charging current

PRODUCT SUMMARY

FEATURES

Cell-balancing control circuit - maximizes pack useful life

Optional external thermistor monitors the pack temperature

Conditioning charging for reviving deeply discharged cells

Timer function available to limit the charging time

Pb-free, RoHS compliant SO-20 package

The SS4035G is a charging control IC designed

for battery packs with two cells in series. When

multiple cells in a battery pack are connected in

series, the weakest cell determines the overall

pack capacity. The SS4035G has a cell-balance

control circuit to solve this problem, and monitors

the voltage of each cell to ensure that no cell is

over-charged. The pulse width modulation (PWM)

output can be used as either a linear or switching

charge-control circuit. Three digital input pins

determine the charge current. All these features

make the charging circuit design easy and flexible.

The SS4035G continuously monitors each cell

voltage, cell current and the battery temperature.

Any unspecified condition will stop the charging

to protect the battery cells. An external negative-

temperature-coefficient thermistor is used as a

sensor to monitor the battery pack temperature.

To be safe, charging is suspended if the voltage

of the temperature sense input pin is higher than

Min Temp Threshold (VTmin) or lower than Max

Temp Threshold (VTmax). When the battery

temperature is within the safe zone, the SS4035G

charges the battery in three phases: pre-charging,

constant-current, or constant-voltage. If the

voltage of the temperature sense input pin is higher

than Low Temp Threshold (Vtlow), or the battery

voltage is less than 3.1V, the SS4035G pre-charges

the battery with a low current.

After the precharging, the SS4035G applies a

constant current to the battery. The value of this

constant current is determined by the levels of

pins S1, S2 and S3 during power up. When

the battery voltage is above the threshold,

the SS4035G begins constant-voltage charging

until the battery is fully charged. The battery is

fully charged when the current drops down to

the termination threshold.

When the cell voltage is higher than the Balancing

Threshold (Vbal), the cell balancing circuit is

triggered if one cell voltage is higher than the

other by more than 0.02V.

DESCRIPTION