SC1766CS08 datasheet(8/11 Pages) SEMTECH

8 / 11 page

652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY

CHARGE CONTROLLER

SC1766

Janaury 30, 1998

PRINCIPLES OF OPERATION (cont.)

MODE PIN

The MODE pin determines the mode in which the IC

works:

MODE

Mode

Function

Floating

NORMAL

normal operation

VDD

TEST

1/512 safety timer

GND

∆V detector reset timer

stops (not reset)

The SC1766 will operate normally when the MODE

pin is left floating (a 0.1µF capacitor is recom-

mended to be tied to the MODE pin if the charge cir-

cuit works in a noisy environment). The SC1766 oth-

erwise works in the following ways if the MODE pin

is biased either to VDD or to GND:

A) AC Mode (MODE pin biased to GND)

In the midst of normal charge operation, where the

VBT pin voltage is in the range from 0.8V to 3.5V

and the preset safety timer has not run out, the

safety timer will stop if the MODE pin is pulled down

to GND level. As long as the MODE pin remains low,

the VOUT pin stays ON and the LED pin OFF re-

gardless of whether the battery pack voltage de-

clines (-

∆V present) or not. AC mode can be acti-

vated by pulling the MODE pin to GND to avoid pre-

mature battery charge cutoff due to fluctuating

charge current source. Switching the MODE pin af-

ter the end of the safety timer has no effect on the

SC1766 display outputs, i.e., VOUT pin stays OFF

while LED pin stays ON.

B) TEST Mode (MODE pin biased to VDD)

A unique feature of the SC1766 is that it can be put

into a TEST mode by pulling the MODE pin to VDD,

allowing verification tests for the SC1766 charge cir-

cuit to be performed in a few tens of seconds, ex-

tremely valuable in the final phase of production.

When the SC1766 is in TEST mode, all the internal

timers are reduced by the following factors when

compared to normal operation:

Safety timer reduced by a factor of 512 times;

Initial timer reduced by a factor of 512 times;

Peak timer reduced by a factor of 64 times.

One critical requirement needs to be observed for the

OPERATION CHART OF THE SC1766

YES

POWER ON

0.65V<VBT<3.7V

OUTgoes high for

trickle charge.

Safety timer and

∆V detector reset.

αNTCL >αNTC

αNTC >αNTCH

OUT goes high for

trickle charge.

∆V detector reset.

Safety timer stops.

OUT goes low for fast

charge.

Safety timer starts

counting.

∆V detector & peak

voltage timer start

working after initial

period ends.

∆V detector & peak

voltage timer working.

αNTCL >αNTC

αNTC >αNTCH

OUT goes high for

trickle charge.

∆V detector reset.

Safety timer stops.

0.65<VBT<3.7V

OUT goes high for

trickle charge.

Safety timer and

∆V detector reset.

Safety timer

period has

finished

Peak voltage

timer period has

finished

0.25% decline

of VBT is

detected

OUT goes to high, fast charge finished, and trickle charge starts.

YES

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