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TPS7B7701-Q1: Vout is not correct

Qin Heater
Prodigy 70 points
Part Number: TPS7B7701-Q1

Dear team,

I have a problem with TPS7B7701-Q1。

The Vout is designed to be 5V，but our team found that one chip outputs about 7V。I measure FB pin is 1.74V，normally it is 1.23V，The chip seems still working。

So can you explan this  phenomena？is there any fault of Vref or EA in chip？ and what external environment can lead to this？

thanks a lot!

Best regards

  • 0
    TI__Mastermind 49585 points

    Hello,

    Can you please share the full schematic? 

    How did you measure VOUT and VREF? Did you use an oscilloscope or a multimeter? Do you have any waveforms to share showing this?

    Thanks,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 70 points

    Hi, Nick

    We found this may caused by external environment not chip fault，before the chip power on，Vout is already above 5V ；

     we remove those external environment，then  power on  device，The Chip working properly。

    So，if that Vout pin above desired voltage bofore power on could make the chip dont work？

    Thanks.

  • +1 in reply to Qin Heater
    TI__Mastermind 49585 points

    Hi,

    I see. Yes, the device does not have a way to sink current into its output, so if there is leakage onto the output that results in VOUT being above the set point the only thing the device can do is close the channel and wait for the output to come down to the regulation point. If the leakage is strong enough that the output capacitor does not discharge to the regulation point, the device will keep the channel closed and do nothing indefinitely. So it's not that the device doesn't work, it's that the device can't do anything about the excess charge.

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 70 points

    Hi,Nick

    Does this like device into reverse current protection or short to battery protection？

    thanks a lot!

    Best regards

  • +1 in reply to Qin Heater
    TI__Mastermind 49585 points

    Hi,

    I believe the short-to-battery detection only registers if the voltage on the output is comparable to the input voltage, and the reverse current protection will only activate when the output is higher than the input. What is the input voltage?

    Regards,

    Nick

  • 0 in reply to Nick Butts
    Prodigy 70 points

    Hi,Nick

    The input voltage is 12V, still higher than Vout voltage. I got it.

    Thanks for helping me figure out all my questions.

    thanks a lot!

    Best regards