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TPS65721 intermittent VSYS drop

Zoltan D
Prodigy 50 points

Dear all,

When using the PMIC with no battery connected and supplied form the AC pins with 5V, I see intermittent VSYS dropouts, causing a system reset. The load is about 200mA on the LDO and 100mA on the DCDC, however the drops don't seem related to the load.

The phenomenon is only showing itself when CH_EN and TERM_EN are both enabled in the CHCONFIG0 register.

Any idea what might cause it or how to circumvent this ?
If the charge and termination should not be enabled when the battery is not connected, how to detect the presence of the battery ?

Thank you,
Zoltan

  • 0
    TI__Genius 16870 points

    Hi Zoltan, 

    I am looking into this report and will reply tomorrow. I believe that the VSYS should not drop out even if you have charge enabled. 

    Is the drop out periodic? If so, what frequency? 

  • 0 in reply to Michael Green
    Prodigy 50 points

    Dear Michael,

    Thank you for looking into this!

    The drops are not periodic, rather random (2-8 sec intervals), but their duration is always 1.8msec.

    Some further findings:
    - I have verified that the voltage at AC does not drop when this happens
    - The PMU does not reset itself, as the register contents are kept as configured
    - The droponly happens when TERM_EN is also enabled
      (i.e. enabling the charger only does not cause a problem)
    - After such an event, the interrupt registers read: 0x10: 0x0D; 0x11: 0xF8; 0x12: 0x0C
    - During normal operation, VBAT rises to 4.2V every 200 msecs. Just before the event, VBAT rises to 5V, then after 20 msecs, VSYS drops, see attached picture (yellow: VBAT, red: VSYS).

  • 0 in reply to Zoltan D
    Prodigy 50 points

    Dear Michael!

    Could you already look into this issue ?

    Thanks.

  • 0 in reply to Zoltan D
    TI__Genius 16870 points

    Do you have a cap or anything else on VBAT?

    This could possibly be caused by if you have a cap out on VBAT. In such an event it could pull from the cap and cause the dropout on the VSYS.