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BQ25703A: Deeply Discharged Battery

Kuramochi Tadahiko
Guru 28715 points
Part Number: BQ25703A

Hi,

My customer is evaluating BQ25703A.

VSYS doesn't start up correctly when the adapter is connected after the battery discharged deeply is connected.

The behavior is improved by the case that the battery is reconnected after the adapter is connected or SRP or SRN pin is shorted with GND momentarily.

This phenomenon does not occur when the battery is not discharged deeply.

What is this behavior caused by?

Please let me know If you have any questions.

Best Regards,

Kuramochi

  • 0
    TI__Genius 11850 points

    Hi Kuramochi,

    The BQ25703A is a NVDC charger with minimum system voltage regulation. Even if the battery is absent or deeply discharged, VSYS should be regulated above the MinSystemVoltage() setting as long as the adapter is present. For example, Figure 48 in the datasheet shows that VSYS is regulated above the MinSystemVoltage() after VBUS is plugged in, even though there is no battery connected.

     

    Is the customer testing a BQ25703A EVM, or are they using their own circuit?

    Also, can you please capture a waveform showing VBUS, VSYS, SRN, and CHRG_OK for each of the following 2 power-up sequences?

    1) Deeply discharged battery already connected, and then the adapter is plugged in.

    2) Adapter already connected, and then the deeply discharged battery is plugged in.

    Best regards,

    Angelo

  • 0 in reply to Angelo Zhang87
    Guru 28715 points

    Hi Angelo-san,

    The customer is testing on their board.

    Could you check the following waveforms?

    >1) Deeply discharged battery already connected, and then the adapter is plugged in.

    >2) Adapter already connected, and then the deeply discharged battery is plugged in.

    They did not capture it because each waveform didn't vary.

    Best Regards,

    Kuramochi

  • 0 in reply to Kuramochi Tadahiko
    TI__Genius 11850 points

    Hi Kuramochi,

    Thanks for capturing the waveform. I'm concerned that CHRG_OK does not go high. CHRG_OK should go high when a good input source is connected to VBUS.

    As a sanity check, can you try plugging in the adapter when there is no system load and no battery connected? Does CHRG_OK go high in this case? We expect to see a waveform very similar to Figure 48 in the datasheet. Can you please read back the ChargerStatus register from the BQ25703A to see if any fault conditions are reported?

    Also, what is your MinSystemVoltage register setting?

    Best regards,

    Angelo