© 1997 SEMTECH CORP.

652 MITCHELL ROAD NEWBURY PARK CA 91320

BATTERY

CHARGE CONTROLLER

SC1766

Janaury 30, 1998

PRINCIPLES OF OPERATION (cont.)

-

∆V detector of the SC1766 to work properly in test

mode, which is that the VBT voltage must be kept be-

tween approximately 2.8V to 3.3V, rather than 0.8V to

3.5V in NORMAL mode.

If the TEST mode function is to be utilized in produc-

tion test, it has to be well planned and included in the

circuit design phase to make the voltages of the VBT

pin and MODE pins extremely controllable. In addition,

an externally controllable TIMER pin can further reduce

the test time required for testing the SC1766 in TEST

mode.

The figure below shows the timing diagram for exter-

nally controlled VBT, TIMER and MODE pin voltages

of a recommended SC1766 charge circuit production

test scheme, utilizing the TEST mode function. Output

waveforms of the VOUT and LED pins (and FLASH pin

for 14-pin version) of a properly functioning SC1766

are also shown in the figure. In time segments 4, 8 and

10, the VOUT pin should change from ON to OFF, the

LED pin from OFF to ON, and the FLASH pin from ON

to flashing output (approximately 4 Hz). For the rest of

the time, the VOUT pin should remain ON, the LED pin

OFF, and the FLASH pin ON. The LED indicators work

as follows:

LED

VOUT

FLASH

PIN

PIN

PIN

Fast Charge

OFF

ON

ON

Trickle Charge ON

OFF

FLASH

VBT Abnormal OFF

OFF

OFF

The LED pin is used in conjunction with the VOUT pin

while the FLASH pin works alone.

Referring to the typical application circuit, the tempera-

ture limits beyond where the fast charge is prohibited

can be set by choosing values for resistors and the

thermistor of the thermistor divider according to the fol-

lowing formula:

R18 = 3.57 R

R19 = 10 R

RT1: Thermistor resistance at low temp. limit

RT2: Thermistor resistance at high temp. limit

Timing Diagram of the SC1766 in the Test Mode