ACT2804 datasheet(14/23 Pages) ACTIVE-SEMI

14 / 23 page

Rev 3, Apr-17-2017

Innovative Power

- 14 -

www.active-semi.com

ACT2804

APPLICATIONS INFORMATION

HYST pin is regulated at 1V. Its input current will

determine hysteresis adjustment equally to all level.

Connect HYST to AGND via a resistor to set

hysteresis window.

Beside the hysteresis window, to avoid comparison

oscillation, fixed 100mV of hysteresis is added to

each LEVEL comparator.

Hysteresis window is given by below equation:

Then RHYST Example is given by the below table:

Battery Impedance Compensation

To avoid the number of LEDs changes between

charge and discharge modes. Internal impedance

compensation circuit is built in. An external resistor

is used to set the impedance from 100mΩ to

800mΩ.

RIMC

corresponding

battery

impedance. The LED1-4 thresholds shifted up and

down based on the product of charge/discharge

current and set impedance. RIMC value is given by

below equation.

In case not using compensation, float RIMC then

there is no compensation affects to trig-points.

RIMC example is given by the below table:

Battery Temperature Monitering

The

ACT2804

monitors

the

battery

pack

temperature by measuring TH voltage at the TH pin

as shows in Figure 4. The TH pin is connected to

the thermistor resistor net which includes a negative

temperature coefficient thermistor. An internal

current source provides a bias current to generate

TH voltage. The ACT2804 compares the voltage at

the TH pin with the internal VTHH and VTHL

thresholds to determine if charging or discharging is

allowed. When VTH<VTHL or VTH >VTHH, it will be

triggered latch off fault, there is 3 ways to wake up

ACT2804 when VTH returns to the normal range.

1. Push PB when latch off bit is not set

2. I2C to clear faults in standby

3. Plug Vin to power up

Figure 4:

Thermistor setting

RNTCc : NTC Resistor at cold temperature (Tcold)

RNTCh : NTC Resistor at hot temperature (Thot)

From (7) (8) (9) and (10) calculate Ra and Rb in

charge mode, as the same method, the resistors in

discharge mode can be calculated.

For example, use NXRT15XH103 NTC resistor, the

temperature in charge mode is 0℃ to 45℃,we

know RNTCC=27.219k and 4.917k at 0℃ to 45℃,

respectively. We can calculate Ra=33kΩ and

Rb=2.87kΩ based on the above formulas. As the

same method we can calculate the value when the

temperature is -20℃ to 60℃.

Cell Balance Setting

ACT2804 has integrated a cell balance feature to

reduce the un-balance charge between dual

batteries. Normally cell balance is activated during

Fast Charge and Top Off modes.

RHYST (kΩ)

LED1

VHYST

LED2

VHYST

LED3

VHYST

LED4

VHYST

Floating

0mV

270

120mV

100mV

135

240mV

200mV

360mV

300mV

67.5

480mV

400mV

600mV

500mV

720mV

600mV

RBAT (mΩ)

100

200

300

400

500

600

700

RCS = 25 mΩ

540k 270k 180k 135k 108k 90k

77k

RCS = 50 mΩ

1080k 540k 360k 270k 216k 180k 154k

 5

HYST





)

(





HYST

54K

HYST

)

(

)

(

)

(

2160

)

(











BAT

IMC

)

(

hot

CHG

TCL





)

(

NTCh

hot









)

(

NTCc

cold









)

(

cold

CHG

TCH





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