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HT7470

Fast Battery Charger

Holtek Semiconductor 

HT7470

Fundamental Function

Charge Function

The charge function of the HT7470 consists of

two periods, the charging period and the status

detection period. During the charging period,

current is supplied to the battery for charging,

while during the status detection period, the

battery voltage and temperature are measured

to determine if the battery is fully charged,

open, shorted or damaged.

Trickle Function (C/10)

When the battery has been detected to have

reached full charge by the HT7470, the charge

rate will switch to trickle charge automatically.

The trickle charge function is dependent upon

the charge inputs and is shown below.

The trickle charge function is different but the

trickle charge rate is identical to C/10. This

function is accomplished by adjusting the

charge duty cycle which is also implemented in

the HT7470. The charge rate KC, is calculated

by the following equation:

K=

Charge current

Battery capacity

C = Battery capacity

Discharge Function

The HT7470 provides a discharge function to

prevent battery memory effect from occuring. If

battery memory effect has occured this function

will eliminate the effect gradually. The dis-

charge input can be selected to discharge the

battery before the charge procedure has

started. When the battery is empty the HT7470

will start the charge procedure automatically.

Warm-up Function

The HT7470 provides a battery warm-up func-

tion to warm up the battery and improve bat-

tery efficiency. The warm-up key is enabled only

in the warm-up waiting period. A low 20ms

pulse in the warm-up waiting period will force

the HT7470 to warm-up the battery. During

this time the discharge input will be inhibited.

The warm-up function is identical to the charge

function.

The warm-up interval is dependent on the

charge rate inputs and is described below:

Charge rate

inputs

4C 2C 1C C/2

S1,S0

11 10 01 00

Charge Count

150 300 600 1200

Time (min)

3.5 7 14 28

During battery warm-up, full charge detection

and abnormal charge detection are always en-

abled.

Full Charge Detection

There are four full charge detection methods

implemented in the HT7470 as described be-

low:

• -∆V detection

• Over Temperature: The TC input pin is logi-

cal low

Trickle Function (C/10)

3

25th Aug ’94

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