AIC1761/1766

BATTERY CHARGE CONTROLLER

SPEC NO: DS-1761-02

ANALOG INTEGRATIONS CORPORATION

www.analog.com.tw

4F, 9 Industry E. 9th Road, Science-based Industrial Park , Hsinchu, Taiwan, R.O.C.

TEL: (8863)577-2500 FAX:(8863)577-2510

6

PIN DESCRIPTIONS

VDD PIN

-

Supply voltage input.

GND PIN

-

Ground.

VBT PIN

-

Input, to sense battery voltage.

MODE PIN -

Input, to set IC operation mode.

TIMER PIN -

Input, for safety timer control.

VREF PIN

-

Voltage reference output.

LED PIN

- Output, for LED indicator.

VOUT PIN

- Output, for LED indicator.

FLASH PIN - Output, for LED indicator.

(Available for 14-pin version only.)

VNTC PIN

- Input, for temperature protection.

(Available for 14-pin version only.)

APPLICATION INFORMATIONS

BATTERY PROPERTIES

The basic principle of rechargeable battery sys-

tems, including NiMH and NiCd cells, is that the

processes of charge and discharge are reversible.

The charge characteristics of NiMH and NiCd

cells look similar in that (1) the cell voltage at the

end of charge drops and (2) the cell temperature

increases rapidly near the end of charge. Fig. 1

shows the charge voltage and charge tempera-

ture characteristics of NiMH and NiCd cells. No-

tice that the cell voltage decline of NiMH cells at

the end of charge is less pronounced than for

NiCd cells.

NiMH

Time (min.)

1.1

1.2

1.3

1.4

1.5

1.6

1.7

Voltage

20

40

50

60

70

80

40

60

100

80

020

NiCd

Charge Current=1C

NiMH

NiCd

Temperature

30

Fig. 1

Typical

Charge

Characteristics

of

NiMH/NiCd Battery

Fast-charge batteries are available where re-

charging takes for only 1 hour or less with a sim-

ple control circuit. One main purpose of the con-

trol circuit is to terminate the fast-charge process

to prevent the temperature and internal pressure

of the battery cell from building up to a damaging

level which degrades or even destroys the battery

cell.

The AIC1761/1766 is a battery fast charge con-

troller IC that utilizes the following methods to

terminate the fast charge process for NiMH or

NiCd battery cells:

Negative delta voltage cutoff (-

∆V).

Peak voltage timer cutoff (0

∆V).

Maximum temperature cutoff (TCO).

Maximum voltage cutoff (VCO).

Safety timer cutoff.

The principle of operation of the AIC1761/1766 is

described in the following section.

THE AIC1761/1766 OPERATION

When power is first applied to the charge system,

consisting of rechargeable battery cells, charge cur-

rent source, the AIC1761/1766 and its associated

external circuit, all internal digital circuit blocks of

the AIC1761/1766 are reset by internal power-on-

reset circuitry. The internal control unit then checks

the battery condition to prevent fast charge from

taking place under battery fault conditions, i.e. cell

perature fault (

αNTC>αNTCL or αNTC<αNTCH, for

the 14-pin version). Temperature fault limits corre-

sponding to

αNTCL and αNTCH are determined by

an external thermistor divider circuit as included in

the Application Examples, Fig. 10. After the battery

passes condition fault checks, VOUT pin goes to

low to start fast charge while initial timer and safety

timer of the AIC1761/1766 start counting. Both the

negative delta voltage detector and the peak voltage

timer, however, are disabled until the initial timer

period in the initial stage of a charge circle elapses.