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TPS65217 voltages too high

Ryan Press46
Prodigy 50 points
Other Parts Discussed in Thread: TPS65217

We have an existing design with many units in the field operating correctly with the TPS65217A supply.  I am doing a failure analysis of one returned unit where the supply has the wrong output voltages before quickly shutting down, about 30% higher than expected.  The INT_LDO and BYPASS pins also have proportionally higher voltages.

I have replaced the IC 3 times with the same result, so it is not a failure of the IC itself.  Any idea what external components or PCB defect could cause this symptom?

  • 0
    TI__Genius 10885 points

    If everything is shifted, I would suspect the reference or ground connections.

    Can you confirm the Thermal Pad, AGND, and PGND are all properly connected?

    BYPASS can be affected by a voltage on the TS pin, is there any path that could be supplying that pin externally?

  • 0 in reply to Richard Solarski
    Prodigy 50 points

    Hi Richard,

    Thanks for your reply.

    I have removed the IC and verified that the pad, AGND, and PGND pins are tied to the ground plane.

    On the TS pin there is nothing connected.  With the IC removed it was high impedance > 10 M ohm.

    Can you elaborate a bit on how the TS can affect the BYPASS?  Even though we don't have a battery, should there be something connected to TS?

    Ryan

  • 0 in reply to Ryan Press46
    TI__Genius 10885 points

    Hi Ryan,

    According to the Schematic Checklist (http://www.ti.com/lit/pdf/slva686), if you are not using a battery you can leave this pin floating.

    Figure 15 of the TPS65217 datasheet shows internal pull-ups connecting TS to BYPASS, which would allow an externally applied voltage on TS to reach the BYPASS capacitor.

    With the PMIC removed can you apply power to the board and confirm the PMIC-supplied rails remain at 0V?

  • 0 in reply to Richard Solarski
    Prodigy 50 points

    Thanks Richard.

    We have 0-ohm resistors on all the PMIC outputs, after the output caps.  I had removed them for testing this unit (maybe no-load could create other problems?) so there was no voltage back-feeding the outputs.

    The outputs do seem to be ramping up properly, they just don't stop at the right voltage and keep going to about 1.3x.  After a short time all outputs turn off.

    Is there a mechanism that will shut down the chip if the output voltages are too high?

    Ryan

  • 0 in reply to Ryan Press46
    TI__Genius 10885 points

    Hi Ryan,

    Not if the output voltages are too high, only the WLED boost has over-voltage protection on the output, the rest of the regulators utilize under-voltage lockout, thermal shutdown, and over-current protections, but will not cause a power-good failure from over-voltage alone.

    However, an over-voltage condition on AC or USB with no battery present can cause the PMIC to shut down. Are these rising conditions strictly limited to the outputs?