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TPS51225EVM-133: Enable testpoint unusable?

Karim Bingoel1
Prodigy 100 points
Part Number: TPS51225EVM-133

Hey team,

So I wanted to control my EVMs with an external circuit. I checked the schematic and came to the conclusion that one has to remove the switch to connect to the Enable testpoints.

If not, the en1/en2 pin would either be pulled to Vreg or gnd. Ok:

For some reason, if the enable2 pin pulled low, I can still measure an output for the 3.3V, same goes for 5V (en1). I even measured 0.00V potential on enable tp.

Before removing the switch the TPS turned on/off just fine. What am I missing?

Thank you

Karim Bingoel

PS: Selecting a proposed part number above doesn’t work on mobile devices (Safari)

  • 0
    TI__Expert 5110 points

    Hi Karim,

    It sounds a little weird. Is there any loading? Maybe the voltage of output cap wasn't discharged?

    I would suggest to directly connect en1/en2 to GND first. It's same as the test with switch that you did before and can help to check if there's some damage with IC.

    If Vout becoms 0V, it seems the failed turn off is caused by the external control circuit. Please double check the connection between EN pin and test point, and double check the EN voltage. I think I need schematic of the external control circuit then for further analysis.

    Regards,

    Andrew 

  • 0 in reply to Andrew Xiong
    Prodigy 100 points

    Dear Andrew,

    firstly thank you for your super quick reply, I read it immediately but could only check on the boards now.

    I just checked my hypothesis that the voltage came from the external circuit and indeed it did. I feel so stupid.. the boards are working fine.

    Thank you & apologies!

    Karim Bingoel

  • 0 in reply to Karim Bingoel1
    TI__Expert 5110 points

    Hi Karim,

    Thanks for your reply. Happy to see you find the root cause.

    Andrew