AIC1782
The AIC1782 provides the function of dis-
charge-before-charge
to
precondition
NiCd
batteries which suffer from memory effect. This
function can only be activated for pack B after
the prequalification of battery voltage and tem-
perature, yet before the charge completion is
registered for 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
TYPICAL
APPLICATION
CIRCUIT.
Fast Charge
After the battery passes fault checks, charge
begins on either of the batteries, the other bat-
tery remains in a waiting state until the first bat-
tery terminates fast charge. The AIC1782 will
automatically switch 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 AIC1782. When fast charging begins, the
initial and safety timer of the AIC1782 start
counting. Functions of -∆V detection, Peak volt-
age timer,
∆
T /
∆
t detection, and maximum
battery voltage are, however, disabled tempo-
rarily until the initial timer period in the initial
stage of a charge cycle elapses. The initial timer
period is equal to 1/80 of safety timer.
Since the low limit of acceptable ABV or BBV
voltage 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 AIC1782 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
∆
V ).
Delta temperature/ delta time (
∆
T /
∆
t ).
Maximum charge time.
Maximum battery voltage.
Maximum battery temperature.
-∆V Cutoff
∆
The AIC1782 makes a voltage sampling at ABV
(or BBV) pin every 4 seconds when 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.
0∆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 3.7% of safety timer, the fast charge ac-
tion is terminated.
∆
T/∆t Cutoff
∆
The
∆
T /
∆
t detection of the AIC1782 is per-
formed by sensing the decrease of ATS (or BTS)
pin voltage in a specific timer interval dictated
by the safety timer. The fast charging termi-
nates when the decrease of ATS (or BTS) pin
voltage in 56 seconds exceeds the predeter-
mined value set by ADJ pin input. This time in-
terval of 56 seconds is based on the assump-
tion that voltage of ATS (or BTS) pin is sampled
once for every 8 seconds, which is also deter-
mined by safety timer.
14
AIC [ ANALOG INTERGRATIONS CORPORATION ]
