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TPS730: internal reference voltage for TPS73001 is not in the datasheet range

Arvinda Reddy
Prodigy 10 points
Part Number: TPS730


I am using TPS73001 in my circuit to generate a 3v power.

below are the usage conditions

IN = EN = 3.3V

R1 = 1.6K

R2 = 1.13K

CNR = 10nF

Cout = 2.2uF

Cff = 471pF

I was expecting output around 3V but getting 2.81V and when I measure Vfb voltage it was around 1.16V and it is less than min internal reference voltage mentioned in datasheet.

i think because of decrease in vfb causing output voltage to decrease.

can anyone tell me what causing Vfb to decrease? 

Regards

Arvinda

  • 0
    TI__Genius 12511 points

    Hi Arvinda,

    Based on typical values and your passive selection I would expect under normal operation for VOUT to be = 2.961V. 

    Are you measuring the voltage at the NR pin as well?

    The NR pin voltage will tell you if what voltage the comparator is referencing Vfb to. If they are both low, then the Vref is too low and the device is not operating properly there is a load on the internal reference not allowing it to get to its intended setpoint. This would indicate that there is some parasitic load upon the NR pin. Is the capacitor having issues with leakage current? Any additional load on that pin from layout parasitics to additional passive connections?

    If the Vfb voltage is low 1.16V and the VNR voltage is as expected than the device should be pushing VOUT high to correct, not low.

    Regards,

    John

  • 0 in reply to John Schneider
    Prodigy 10 points

    Thank you john for the reply.

    voltage at the NR pin also below the expected. its actually 1.146V when I measure.

    I detected this issues in production. producing thousands of board with the same device and same layout.

    almost all the board are giving around 3.0V output as expected but only this board is giving 2.81V.

    so wanted to check if there is any error in the design.

    as you also mentioned, I think may be this particular device is not working properly. 

    any extra comments are welcome.

    Regards

    Arvinda

  • 0 in reply to Arvinda Reddy
    TI__Genius 12511 points

    Hi Arvinda,

    I do not see any glaring flaws in the information that you have presented. Especially not any operation that would cause the sag that you have seen on your failing board. I also cannot find any outstanding reliability concerns with the device or returns for device failures.

    One test that would be useful is if possible to perform an ABA swap. this would help narrow down whether it is something with the part or something went wrong with the board.

    Regards,

    John

  • 0 in reply to John Schneider
    Prodigy 10 points

    thank you john for the reply.

    yes I am planning to do ABA swap to check and decide whether board went wrong or part went wrong.

    Regards

    Arvinda

  • 0 in reply to Arvinda Reddy
    TI__Genius 12511 points

    Hi Arvinda,

    Ok, it will be useful to know the results. Please keep me updated.

    Regards,

    John

  • 0 in reply to John Schneider
    Prodigy 10 points

    Hello John,

    this problem is resolved.

    looks like there was some assembly/soldering issue.

    voltage level returned to expected level when additional solder paste is added. 

    thank you for your support.

    regards

    Arvinda kumar

  • +1 in reply to Arvinda Reddy
    TI__Genius 12511 points

    Hi Arvinda kumar,

    Excellent, I'm glad to see that the device is working as expected. Please let me know if any other problems arise with the device operation.

    Regards,

    John

  • 0 in reply to John Schneider
    Prodigy 10 points

    Thank you for your support.

    I will let you know if I have any doubts related to TI chips in future.

    Thank you

    Arvinda kumar