HT7470 Просмотр технического описания (PDF) - Holtek Semiconductor

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HT7470

Fast Battery Charger

Holtek Semiconductor 

HT7470

• Safety Timer Overflow: Internal event

counter has overflowed

Charge rate

inputs

4C 2C 1C C/2

S1,S0

11 10 01 00

Charge Count 1200 2400 4800 9600

Time (min)

28 56 112 224

• Battery Maximum Voltage Protection

If any of the conditions described above oc-

cur the charge rate will switch to trickle

charge automatically.

Abnormal Charge Detection (Open, Short, Bat-

tery Damage)

The HT7470 can detect abnormal battery states

which include charge loop open or short, battery

high impedance or short. There is a precharge

procedure to pull-up the battery voltage for the

detection of abnormal states. The HT7470 pre-

charges the battery and looks for abnormal

states before the charge procedure begins. The

detection of abnormal states is always enabled

when the charge procedure is running. Any ab-

normal state will force the HT7470 to enter the

abnormal mode and display the corresponding

indicator or turn on the buzzer. In abnormal

mode the HT7470 stops charging until the ab-

normal battery is removed or the charge loop is

open.

A/D Converter

The battery voltage is read into the HT7470

through a 12 bit wide integral type A/D con-

verter. The resolution of the A/D converter is 68

µs/count (1MHz system clock).

Auto - Start and Reset Key (RST)

The HT7470 can detect whether the battery is

ready or not. When the battery has been de-

tected to be ready the HT7470 charge procedure

will run automatically. The RST pin is used for

system initialization. This reset pin has an in-

ternal pull-high resistor. In order to guarantee

all circuits are reset it is combined with an

external 0.1µF capacitor to provide an internal

reset pulse. If the charge loops is open the

HT7470 will enter the stand-by mode. In this

mode the HT7470 continues to detect whether

the battery is ready or not.

Charge and Discharge Inputs

Charge rate inputs: 4C, 2C, 1C, C/2

S1 and S0 are the charge rate inputs with inter-

nal pull-high resistors. The HT7470 adjusts the

internal parameters such as safety timer,

trickle charge duty cycle, and warm-up interval

by referring to these charge rate inputs to make

the system safe. These charge rate inputs are

determined by the external charge current. The

relationship between the inputs “S1,S0” and

charge rate are listed in the following table.

Charge rate inputs 4C 2C 1C C/2

S1,S0

11 10 01 00

Discharge Input: Discharge before charge pro-

cedure.

The DCHI pin is the discharge input with inter-

nal pull-high resistor. The user can force this

pin low to select the discharge function of the

HT7470.

Warm-Up Key

The WARM pin is the warm-up input with in-

ternal pull-high resistor and 20ms debounce

time.

The warm-up function is activated by a low

pulse on the WARM pin. The pulse width must

be larger than 20ms during the warm-up wait-

ing period.

Note that the discharge input will be inhibited

if the warm-up key is pushed.

The charge and discharge inputs are enabled

until the warm-up key is pushed or until the

end of the warm-up waiting period.

4

25th Aug ’94

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