SS6781ACNTB datasheet(9/18 Pages) SSC

9 / 18 page

www.SiliconStandard.com

9 of 18

SS6781A(G)

1/11/2005 Rev.2.10

APPLICATION INFORMATION

OPERATION OF THE SS6781A

Power-on and Battery Pre-qualifying

When power is first applied to the SS6781A, all

internal digital circuit blocks of the SS6781A are

reset by the internal power-on-reset circuitry and

output LEDs (depending on the setting of SEL1 and

SEL2 pins) flash 3 times to indicate the initiation of

power-on. The internal control unit then examines

the battery condition through the VBT and VTS

pins.

The acceptable limits of VBT pin are determined by

the input voltage of SEL3 pin and the acceptable

temperature sense voltage window for VTS pin is

0.29 VCC to 0.72 VCC. If the voltage of VBT pin fails

to fall within the predetermined acceptable limits,

the SS6781A enters a charge-suspending mode, in

which all the internal circuitry remains in reset state.

If the voltage of VTS pin is outside the 0.29 VCC to

0.72 VCC window, action of SS6781A is determined

by the input voltage of SEL3 pin.

Discharge-Before-Charge

The

SS6781A

provides

the

function

discharge-before-charge

precondition

NiCd

batteries which suffer from memory effect. This

function

can

only

activated

after

the

pre-qualification of battery voltage and temperature,

but before the charge completion is registered for

the fast charge cycle.

To trigger this function, DSW pin has to be biased

to GND for over 0.18 second. After discharge

begins, LED1 and LED2 pins are both off, ICON

pin is on, and DIS pin goes high to activate an

external circuit to discharge the battery until the

voltage of VBT pin falls 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. Fast charge will automatically start after

discharge is finished. The application circuit is

included in TYPICAL APPLICATION CIRCUIT.

Fast Charge

After the battery passes fault checks and required

discharging of the battery is completed, fast

charging begins while initial timer and safety timer

of the SS6781A start counting. Functions of -

∆V

detection, peak voltage timer,

∆

detection,

and

maximum

battery

voltage

are,

however,

disabled temporarily 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 VBT voltage is

only about 0.16V during the initial timer period,

even deeply discharged batteries can easily qualify

to be fast charged subsequently.

In the course of fast charge, the SS6781A

constantly monitors the voltages at VBT and VTS

pins. The fast charge process is switched to trickle

charge when any one of the following situations is

encountered, which are explained below:

l Negative delta voltage (-

∆V)

l Peak voltage timer (0 V

∆ )

l Delta temperature/ delta time (

∆T/∆t)

l Maximum charge time

l Maximum battery voltage

l Maximum battery temperature

∆V Cutoff

The SS6781A makes a voltage sampling at VBT

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

VBT 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 determined

SS6781ACNTB Datenblatt(PDF) 9 Page - Silicon Standard Corp.

SS6781ACNTB Datenblatt(HTML) 9 Page - Silicon Standard Corp.

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18

Datenblatt Download

Link URL