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TPS2662: TPS26625 no OVP shutdown

Peter Reiter
Prodigy 80 points
Part Number: TPS2662

We use following schematic:

R4, R5, R6, T1-A, C3, R7 is application specific.

We start with UVLO appr. 9,8V and OVP 30V; I_OUT > 0,8A; dVdT appr. 100ms.

With calculation sheet "TPS26625 - Design Calculator Rev1p0.xlsm" we get R8(R1)=620kR(619,6kR); R9(R2)=100kR(98,6kR); R2(R3)=30kR(30kR).

1st problem: The calculation sheet does not consider the max. voltage of 3,5V (for low leakage current) at the UVLO pin, therefore we use now 680kR; 62kR and 30kR (for the first step okay).

2nd problem: We have shortet EPAD with GND and not EPAD and RTN-Pin, but we have no return voltage, therefore no problem.

3rd problem: UVLO is working, but we have no OVP shutdown and we cannot see the source of this failure (tested without D1 ;-). Please help.

Kind regards

Peter

  • 0
    TI__Expert 5575 points

    Hello Peter

    Your findings about calculation sheet are correct. The current revision of calculation sheet does not incorporate for max UVLO voltage. We will update this sheet to flag when device ROC is violated.

    On OVP cut off issue I would like to know following

    1. Please monitor OVP voltage. Please share a scope shot showing VIN, VOUT, FLT and OVP pin.

    2. I would like to check if you are not using any other variant of TPS2662. This could be because of the parts wrongly shipped to you or different variant used at your end. Please check top side marking of the device. 

    Thanks & Regards

    Abhijeet

  • 0 in reply to Abhijeet Godbole
    Prodigy 80 points

    Dear Abhijeet,

    thanks for your help.

    @ top side marking

    1st line: ED05

    2nd line: 978

    3rd line: A61R

    @ scope shot

    Screen shot of scope not possible, we use an adjustable power supply.

    nFLT with 100kR connected to pin VOUT

    RTN-Pin connected to EPAD; GND is now System-GND.

    VIN(1) - [V] VOUT(10)- [V] ULVO(2)- [V] OVP(3)- [V] nFLT(9)- [V] Information
    9,292 0,335 1,101 0,357 0,0 under ULVO threshold voltage rising
    11,006 11,006 1,304 0,424 10,9 over ULVO threshold voltage rising
    28,643 28,643 3,399 1,104 28,4 under OVP threshold voltage rising
    33,99 33,99 4,026 1,307 33,67 over OVP threshold voltage rising
    50,05 50,05 4,789 1,555 49,6 over OVP threshold voltage rising

    Kind regards

    Peter

  • 0 in reply to Abhijeet Godbole
    Prodigy 80 points

    Dear Abhijeet,

    thanks for your help.

    @ device marking

    1st line: ED05

    2nd line: 978

    3rd line: A61R

    @ monitoring OVP voltage

    Screen shot of scope not possible, therefore we use an adjustable power supply.

    Pin nFAULT now with 100kR to VOUT, Pin RTN is now connected to EPAD, connection EPAD to GND open, GND is System-GND.

    VIN(1) - [V] VOUT(10) - [V] UVLO(2] - [V] OVP(3) - [V] nFAULT(9) - [V] Information
    9,292 0,335 1,101 0,357 0,0 under ULVO voltage threshold rising
    11,006 11,006 1,304 0,424 10,9 over ULVO voltage threshold rising
    28,643 28,643 3,399 1,104 28,4 under OVP voltage threshold rising
    33,99 33,99 4,026 1,307 33,7 over OVP voltage threshold rising
    50,05 50,05 4,789 1,555 49,6 over OVP voltage threshold rising

    Kind regards

    Peter

  • 0 in reply to Peter Reiter
    TI__Expert 5575 points

     compared EVM device tOVP cut-off response on TPS26625 EVM. Please see below waveform. 

    VIN Nominal: 28V

    VIN- OVP SET: 33V

    I do not see any issue with your schematic either. Can you try replacing part with new one. Just to make sure device OVP pin is not damaged or there is no connection issue as such

    Thanks & Regards

    Abhijeet

  • 0 in reply to Abhijeet Godbole
    Prodigy 80 points

    Dear Abhijeet

    We have now tested ..

    R1 (nSHDN) C1 (dVdT) description
    100kR 220nF no OVP cut off
    100k DNP no OVP cut off
    DNP DNP OVP cut off is working
    DNP 220nF OVP cut off is working

    Therefore  we use no pullup resistor at pin nSHDN.

    Thanks for help.

    Kind regards

    Peter