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Original question:

TPS7A8101: TPS7A8101 output before Enable

TPS7A8101: Output voltage higher than expected

Joel Brown
Intellectual 280 points

Part Number: TPS7A8101

Tool/software:

We are using TPS7A8101 with 31.6K / 10K feedback resistors. Output should be 3.328V but it is going to 5V and damaging components on 3.3V supply.

This has happened on multiple boards. Need a urgent response as our project is stopped and we have to replace damaged parts.

  • 0
    Intellectual 280 points

    Here is some new information. Output voltage measured on three different boards: 5.1V, 3.31V, 2.7V increasing slowly in 5 minutes increased to 3.1V

  • 0 in reply to Joel Brown
    TI__Genius 17700 points

    Hi Joel,

    Your TPS7A8101 design looks fine, I don't see anything there that I'd expect to cause this issue. Are there any areas in your design where another supply could bridge to the +3V3_STBY?

    Additionally, I'd like to rule out assembly issues - poor solder joints on R252 or U51 Pin 3 could cause the LDO to lose its feedback connection, in which case the output would rise to approximately Vin. A bridge from pin 6 to pin 7 could also cause this behavior, effectively changing the internal reference voltage to 5V. Can you check resistance between pins 1/2 and pin 3, pin 3 to GND, pin 6 to +5V0_STBY, and pin 6 to GND on a failing board? If possible, can you also take voltage measurements at pin 3 and pin 6 on a failing board? 

    Best Regards,

    Alex Davis

  • 0 in reply to Alex Davis
    Intellectual 280 points

    We think the problem maybe that the trace for the FB signal is routed underneath the 10uF output capacitor (C359) and somehow there is leakage from the capacitor to the FB signal. We removed the output capacitor on one board and it fixed the problem. Still not 100% sure yet this is the problem.

  • 0 in reply to Joel Brown
    TI__Genius 17700 points

    Hi Joel,

    Leakage is possible, but would need to be significant. If the feedback net has leakage to GND beneath C359, the equivalent resistance of that leakage would need to be less than 15kΩ in order to raise the output voltage to 5V. 

    Best Regards,

    Alex Davis