SS6782G datasheet(10/19 Pages) SSC

10 / 19 page

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10 of 19

SS6782G

9/21/2005 Rev.3.01

tion to be taken is determined by the input

volt

age of SEL3 pin.

Discharge-Before-Charge

The SS6782G provides the function of discharge-

before-charge to precondition NiCd batteries,

which can suffer from a memory effect. This

function can only be activated for pack B after

the prequalification of battery voltage and tem-

perature, but before the charge completion is

registered for a fast charge cycle of pack B.

To trigger this function, DSW pin has to be bi-

ased to GND over 0.18 second. After discharge

begins, LEB1 and LEB2 pins are both OFF,

ICOB pin is ON, and DIS pin goes high to acti-

vate an external circuit to discharge the battery

pack B until the voltage of BBV pin fall below

0.9V (or 0.69V, depending on the input voltage

of SEL3 pin) or DSW pin is biased to GND for

over 0.18 second again. The application circuit

is included in the TYPICAL APPLICATION

CIRCUIT shown on page 2.

Fast Charge

After the battery passes fault checks, charging

begins on either of the batteries, and the other

bat

tery remains in a waiting state until the first

bat

tery terminates fast charging. The SS6782G

automatically switches to fast charge the second

battery. The battery pack A has the priority over

battery pack B only when power is first applied

to the SS6782G. When fast charging begins, the

initial and safety timer of the SS6782G start

counting. The -

∆V detection, peak voltage timer,

∆

detection, and maximum battery voltage

functions

are, however, disabled temporarily

until the initial timer period in the initial stage of

the

charging cycle elapses. The initial timer period

is equal to 1/80 of safety timer.

∆

T/ t

Since the low limit of acceptable ABV or BBV

voltages are only about 0.16V during the initial

timer period, even deeply discharged batteries

can easily qualify to be fast charged subse-

quently.

In the course of fast charge, the SS6782G con-

stantly monitors the battery voltage and tem-

perature through ABV (or BBV) and ATS (or

BTS) pins. The fast charge process is regis-

tered complete when any one of the following

situations is encountered, which are explained

below:

Negative delta voltage (-

∆V).

Peak voltage timer (0

∆

Delta temperature/ delta time (∆

∆

T / t ).

Maximum charge time.

Maximum battery voltage.

Maximum battery temperature.

∆V Cutoff

The SS6

782G makes a voltage sampling at ABV

(or BBV) pin every 4 seconds when the safety timer

period is set equal to 80 minutes. If a negative

delta voltage of 0.25% compared to its peak

value is detected at ABV (or BBV) pin, the fast

charge cycle is terminated.

∆V Cutoff

If the battery voltage stays at its peak value or

decreases very slowly for the duration deter-

mined by the peak voltage timer, which is in

turn equal to 3.7% of the safety timer, the fast

charging

action is terminated.

∆T/∆t Cutoff

The ∆

∆

T / t detection of the SS6782G is per-

formed by sensing the decrease of ATS (or

BTS) pin voltage in a specific timer interval dic-

tated by the safety timer. The fast charging

terminates when the decrease of ATS (or BTS)

pin voltage in 56 seconds exceeds the prede-

termined value set by ADJ pin input. This time

interval of 56 seconds is based on the assump-

tion that the voltage of ATS (or BTS) pin is sampled

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