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TPS2491DGS

Shahram Shariat Panahi
Prodigy 40 points
Other Parts Discussed in Thread: TPS2491

Hi,

I am working with a TPS2491DGS as a 48V power supply hot swap controller. I am finding that the chip reference voltage on pin 2 is about 1.2V instead of 4V. VCC at pin 10 is 47.5V and Enable at pin 1 is 3.3V. I have used many chips and the result is the same. I have also separated pin 2 from the PCB the pin and Vref is still 1.2V.

Can the connection from the sense resistor to the IC affect the reference voltage on pin 2 ?

Thank you.

Shahram

  • 0
    TI__Mastermind 42795 points

    Can the connection from the sense resistor to the IC affect the reference voltage on pin 2 ?

    I don't think so. Can you try to install a non-working chip on the TI EVM? It may be that the chip is damaged prior to installation on your PCB or damaged after power is applied for the first time.

  • 0 in reply to Eric Wright
    Prodigy 40 points

    I don't have a TI EVM. The chip was replaced on my PCB many times with the same result. I have even lifted up the pins 2 and 3 to separate them from the PCB. The result is still the same. The 48V at Vcc looks ok. According to the datsheet, the Vref should be there, but It is not.. I just found out that the Vref changes with the output load. Very weird.

    Any help is appreciated.

    Thanks

  • 0 in reply to Eric Wright
    Prodigy 40 points

    I checked the load dependence of Vref. Vref is about 4V when the output load is between 50 and 70 mA. Out of this range, Vref drops to about 1.2V.

     

    Regards

  • 0 in reply to Shahram Shariat Panahi
    TI__Mastermind 42795 points

    The behavior you describe is indeed strange for a part this mature (millions sold with never a report of a problem like this). I suggest running side by side evaluations between your board and the EVM (this will provide clues to what is wrong on your PCB).

    If you need an EVM, I can send one to our Austin TI office so they can hold it for you.

  • 0 in reply to Eric Wright
    Prodigy 40 points

    Hi Eric,

     

    Thank you very much for your answer. What you mention is correct. It is a strange problem and I think it is PCB related. The same circuit worked properly on our older prototype board. Very similar circuit works on the PCB under test, but this particular channel does not work.

    I think the only way to find the problem is knowing what can affect the reference voltage of the TPS2491. So, is there anything OTHER than UVLO and POR thresholds that can prevent the IC to produce the correct Vref voltage ?

    I appreciate your help.

    Regards

    Shahram

     

  • 0 in reply to Shahram Shariat Panahi
    Prodigy 10 points

    I'm interested in finding out if this problem was resolved. I'm having nearly the exact same issue, except that my circuit VCC is 24V instead of 48V.

    I don't believe the chip itself is damaged as I've swapped the IC with an older prototype board and the issue stayed with the newer, bad board (did not follow the IC).

    So yes, what else can affect the IC reference voltage?