Start Safety Timer

Charge Done?

No

STAT = Hi

Update STAT

bits

I2C Read/Write

performed?

Start 30 second

watchdog timer

No

Yes

30s timer expired?

No

Yes

Received SW watchdog

RESET?

No

Yes

Safety timer expired?

No

Yes

Safety timer

fault

Charging suspended

Enter suspended

mode

Fault indicated in

STAT registers

Yes

Charge Done?

No

STAT = Hi

Update STAT

bits

Yes

Reset 30 second

watchdog timer

Reset to default

values in I2C

register

Restart 27min

safety timer

Safety timer expired?

Safety timer

fault

Charging suspended

Fault indicated in

STAT registers

No

Yes

bq24273

www.ti.com

SLUSB08 – JUNE 2012

second timer is reset by the host using the I2C interface. This is done by writing a “1” to the reset bit (TMR_RST)

in the control register. The TMR_RST bit is automatically set to “0” when the 30-second timer is reset. This

process continues until battery is fully charged or the safety timer expires. If the 30-second timer expires, the IC

enters DEFAULT mode where the default register values are loaded, the safety timer restarts at 27minutes and

timer as long as the 27 minute safety timer has not expired. The watchdog timer flow chart is shown in Figure 3.

Figure 3. The Watchdog Timer Flow Chart for bq24273

Hardware Chip Disable Input (CD)

The bq24273 contains a CD input that is used to disable the IC and place the bq24273 into high-impedance

mode. Drive CD low to enable charge and enter normal operation. Drive CD high to disable charge and place the

bq24273 into high-impedance mode. Driving CD high during DEFAULT mode resets the safety timer. Driving CD

high during HOST mode resets the safety timer.

Copyright © 2012, Texas Instruments Incorporated

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