BQ25731: What is 256 mA Current in Forward Mode?

johny radio

Expert 1280 points

Part Number: BQ25731

The datasheet says:

"9.4.1 Forward Mode:
charge current will reset to 256 mA after watch dog timer expires"

Why 256 mA? What is the purpose of that current?

over 2 years ago

0 Md Munir Hasan over 2 years ago

TI__Expert 3335 points

Hi Johny,

The charging current resets to a default value after the watchdog timer expires. The host is responsible for terminating the charge if the battery is not in good condition to charge for example bat short. In case the host fails to terminate the charge or change the charge current, the charger defaults to a safe low current of 256mA so that it does not damage the battery and prevent the risk of fire.

Best Regards,

Munir

0 johny radio over 2 years ago in reply to Md Munir Hasan

Expert 1280 points

For example, bat short? How is ANY current safe with a short?

0 Md Munir Hasan over 2 years ago in reply to johny radio

TI__Expert 3335 points

Hi Johny,

Bat short does not mean completely short. If the battery voltage is below a certain threshold, it is considered bat short. When that happens low charging current is deployed as protective measures. The datasheet section 9.3.21.7 describes BQ25731's own bat short protective measures which reduces the maximum charging current to 384mA. When the watchdog timer expires charging current goes to a default low value.

Best Regards,

Munir

0 johny radio over 2 years ago in reply to Md Munir Hasan

Expert 1280 points

What starts the timer?

0 Md Munir Hasan over 2 years ago in reply to johny radio

TI__Expert 3335 points

Hi Johny,

It is a dedicated timer called the watchdog timer. You can set the timer timeout value to 5s, 88s or 175s. Timer will start again whenever it times out.

Best Regards,

Munir

0 johny radio over 2 years ago in reply to Md Munir Hasan

Expert 1280 points

the timer is running continuously, regardless of battery voltage or current?

0 Md Munir Hasan over 2 years ago in reply to johny radio

TI__Expert 3335 points

Hi Johny,

Not continuously. After the timer times out it will start again once ChargeCurrent() and ChargeVoltage() commands are sent. After that when it times out, charge current will be reset to 256mA and timer will stop. Timer will not start again until those commands are sent again. Updating the watchdog timer value also start the timer again. Sorry about my answer not being clear earlier.

Best Regards,

Munir

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BQ25731: What is 256 mA Current in Forward Mode?