BQ25308: Inquiry about charging when the battery is completely discharged in BQ25308

Grady Lee

Part Number: BQ25308

Tool/software:

Hi, TI expert

The customer is reviewing the BQ25308, and the battery used is 1 cell, lithium polymer.

The customer said that he conducted the test after forcibly discharging the battery completely, considering the possibility of natural discharge later.

Currently, when the battery is completely discharged, the 3rd pin (STAT) of BQ25308 is repeatedly going from low to high to low to high.

It is shown as Fault mode of STAT pin.

If the battery is completely discharged, does it not charge?

Is there a way to charge a completely discharged battery?

Please check

2 months ago

0 Ning T 2 months ago

TI__Guru 57621 points

Hi,

Is there any battery protection circuitry in between the BAT pin and the battery pack or does the battery have built-in battery protection? The battery under-voltage protection may disconnect the battery from the BA pin of the charger.

Thanks,

Ning

0 Grady Lee 2 months ago in reply to Ning T

Genius 4185 points

Hi,

As for the circuit diagram, it is attached to the previous question and was reviewed at that time.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/1473690/bq25308-request-for-bq25308-schematic-review

In this case, if there is a built-in protection function in the battery, does that mean that charging is possible?

The customer said that he forcibly discharged the battery to make it a 0V battery and conducted a test.

However, the STAT pin is repeating low to high to low to high like Fault mode.

If charging is possible, can you explain the method in detail?

Thank you.

0 Ning T 2 months ago in reply to Grady Lee

TI__Guru 57621 points

Hi,

The BQ25308 has no battery detection feature. It will regulate the output even if a battery is not connected. Please refer to the FAQ below and the principle is similar.

[FAQ] BQ25601: [FAQ] Why does the LED connected to STAT pin flashes and the SYS voltage unstable when battery is not connected for BQ25601, BQ25601D, BQ25606, BQ25611D, BQ25616, BQ25616J, BQ25618, BQ25619, BQ25600, BQ25600D, BQ25600C?

Thanks,

Ning.

0 Grady Lee 2 months ago in reply to Ning T

Genius 4185 points

Hi,

Ning T said : The BQ25308 has no battery detection feature. It will regulate the output even if a battery is not connected.

→ The charger ICs listed in the [FAQ] link mentioned do not seem to have a "Dead Battery Charge Inhibit" function.

In the case of the BQ25308, the "Dead Battery Charge Inhibit" function is listed as a safety function in the datasheet.

According to the datasheet, when "charge inhibit" is activated, the charging current is -1.5uA and charging is not possible.

Q1) Nevertheless, does this mean that the charging function is activated even for a completely discharged battery (0V) in the case of BQ25308?
If so, if I continue to charge, will the battery voltage increase, although it will take a long time?

Q2) If charge inhibit is true for a completely discharged battery (0V) in the case of BQ25308, do I need to replace the battery?

Thank you.

0 Ning T 2 months ago in reply to Grady Lee

TI__Guru 57621 points

Hi,

When the STAT pin of BQ25308 is repeatedly going from low to high to low to high with the completely discharged battery connected to the BAT pin, could you please monitor the BAT pin voltage? And what's the BAT pin voltage?

Thanks,

Ning

0 Grady Lee 2 months ago in reply to Ning T

Genius 4185 points

Hi,

It is said that the BAT pin voltage is measured as 0V without any change.

Thanks

+1 Ning T 2 months ago in reply to Grady Lee

TI__Guru 57621 points

Hi,

In this case, the device does not charge as the d/s describes.

Thanks,

Ning.

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BQ25308: Inquiry about charging when the battery is completely discharged in BQ25308