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TPS7B7702-Q1: Part failing after 28V applied to OUT1 or OUT2 pin

Theo Kachelski
Prodigy 95 points
Part Number: TPS7B7702-Q1

Tool/software:

Hello we use the TPS7B7702QPWPRQ1 as 2 5V sensor supplies on our product.  During an >28V overvoltage condition on either OUT1 or OUT2 the part fails.  I am curious as to why because the data sheet says that it can handle up to 45V on the out pins. 

Our theory is that even though OUTx can go to 45 volts that the FBx will over voltage due to the voltage divider we use to get to 5V regulated output.  The overvoltage on the FBx is 7V.

Do we need a zener diode or some clamp on the FBx pins to protect against this condition? This is what we believe we need (diode in orange)

We probed the pin 1 (blue arrow) when introducing a 28V conidtion on out 1 and this is a capture of that event.  (pin 1 is fed by a 6.5V regulated supply)

Pin 1 went from 6.5 to 12.1 volts then decayed for about 3ms.  After this the chips out1 rail was held at 0-.1V.  

Is our analysis correct and do we need a clamp on the FBx pins to protect against this?

  • 0
    TI__Guru 50025 points

    Hi Theo,

    My first thought is that the FB pin abs max was being violated as well but unless there is some overshoot I calculate 6.9V, and even though that's close it doesn't appear to be a violation. Another explanation for this that fits your description and the waveform you included is that the device may not be damaged but rather has latched its output off after the reverse voltage event that causes reverse current to flow. Section 7.3.3 describes how the reverse current detection works; what I'm seeing is that once the 28V is applied, some current flows through the channel to the input and then after some time the device stops the reverse current, and then you mentioned that the output goes back to ~0V. All of this aligns with how the reverse current protection works. Have you tried toggling the EN pin to restart the device? 

    By the way, if it is indeed a reverse current protection even that's happening here and not an abs max violation, you will need a way to toggle EN because this device was designed to keep its output latched off after a reverse current event indefinitely until EN is toggled. 

    Regards,

    Nick