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TPS65218: TPS65218 Coin cell excessive backup current

Gush Bhumbra
Prodigy 200 points
Part Number: TPS65218

I am using the TPS65218 PMIC to power the RTC on the AM4372 on our custom board. I was surprised to see the PMIC draw 160uA when powering the 1.8V and 1.0 RTC rails. What current should I expect the PMIC to take while supplying the processor? The circuit is the same as the GP-EVM, as far as I can tell. On another EVM only 4uA is consumed.

I have noticed that the 1.8VD rail from the PMIC is not at 0V but slowly rises to 0.2V. As this rises the current consumption from the 3V coin cell drops from 200uA to 160uA. If I short the 1.8VD output rail from the PMIC to GND, the consumption rises again to 200uA. The 1.8V_RTC and 1.0V_RTC are correct. All the other output rails from the PMIC are 0V. I have previously submitted our schematics to Biser. I did try changing the RTC_KALDO_EN pin on the AM4372 at 1.8V and GND and the current consumption does not change.

I also disconnected the AM4372 power rails from the 1.8VD line and the PMIC (TPS65218B1RSLT) continues to increase the 1.8VD output rail to over 1.0V and the current consumption from the coin cell continues to decrease to 70uA.

I have tried this on 6 boards. Two consume 200uA immediately after power down from the 3V coin cell. 2 consume 90uA immediately after power down. All six boards are the same hardware.

  • 0
    TI__Intellectual 1020 points
    Hello,
    Thank you for posting your question on the TPS65218 in the e2e forum.
    Your thread has been assigned to the expert within TI, who will reply to your question as soon as possible and attempt to resolve your issue.

    Best regards,
    Eran
  • 0
    TI__Expert 4155 points
    Gush,

    I have looked it over and it looks like the CAP_VDD_RTC pin can pull up to 2mA or current, and the VDDS_RTC pin can pull up to 5mA of current. Given this I don't think it is unreasonable to see the PMIC pull 160uA from the coin cell. If changing the RTC_KALDO_EN pin did not change the current draw then it would be unlikely that the CAP_VDD_RTC pin would be pulling much current, but without knowing how much current the VDDS_RTC pin is pulling it would be hard to say whether or not the 160uA is higher than expected. Even if the PMIC was 100% efficient though the 160uA pull could be expected if VDDS_RTC was pulling 293uA. (just using Pin=Pout)

    When you say that 1.8V rail was slowly increasing from 0V when exactly is this occurring? This is what really seems strange to me.

    If you want to send me a schematic to look at I would be happy to look it over.

    Thank you,
    Nick
  • 0 in reply to Nick Jakse49
    Prodigy 200 points

    I worked what the issue was. I had copied the rev 1.4 schematic of the GP-EVM437x eval board which has a pull up resistor from PGOOD_BU to V1.8D. This pin is a push pull not open drain and ends up feeding the LDO1 output (V1.8D) rail. When this resistor is removed the current draw drops to a more acceptable 4uA.

  • 0 in reply to Gush Bhumbra
    TI__Expert 4155 points
    That is great to hear! I am glad you were able to solve this yourself.

    If there is anything else you need please let me know.

    Thank you,
    Nick