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TPS65381-Q1 VDD1_SENSE Bias current

masahiko shimizu
Guru 11235 points

Hi

Could you let me know VDD1_SENSE Bias current?

My customer used 20k-ohm and 39k-ohm as divider register.
Then VDD1 output was 1.035V.
But output calculated value is 1.2V at using 20k-ohm and 39k-ohm as divider register.
After that, my customer changed divider register from above value to 40-ohm and 80-ohm.
Then VDD1 output was 1.2V.
I think that this cause is VDD1_SENSE Bias current.
I'd like to know VDD1_SENSE Bias current.

Best regards
Shimizu

  • 0
    TI__Mastermind 20580 points

    We will check on it and get back in a few days.

    - Scott

  • 0 in reply to Scott Monroe
    Guru 11235 points

    Hi

    Thank you for your support.
    I wait for your reply for a few days.

    and I would like to know VSFB1 Bias current, too.
    Could you let me know VSFB1 Bias current in case of tracking mode?


    Best regards
    Shimizu

  • 0 in reply to masahiko shimizu
    TI__Mastermind 20580 points

    Hi Shimizu-san,

    I have confirmed with some of our team the impact the customer is seeing is linked to the needed bias current of VSFB1 to operate correctly.  Unfortunately at this time I don't have the minimum needed current and will be asking for further support from our teams to be able to give better guidelines on this topic in the future.  This will take some time.

    Thanks,

    Scott

  • 0 in reply to Scott Monroe
    Guru 11235 points

    Hi Scott-san

    Thank you for your support.

    The feedback bias current of an output variable type DC/DC or LDO is always suggested in datasheet.
    This information is important for decideing FB divider.
    Please confirm the feedback bias current as soon as possible.

    Best regards
    Shimizu

  • 0 in reply to masahiko shimizu
    Guru 11235 points

    Hi Scott

     Thank you for your support.

     Any update on this?

    Thanks

    Shimizu

  • 0 in reply to masahiko shimizu
    TI__Mastermind 20580 points
    Hi Shimizu-san,

    The bias current from the VDD1SENSE pin is approximately 8.5uA. The offset voltage due to this is calculated: Voffset = R2 * 8.5u which in the customer case matches their measurements: Voffset = 20k * 8.5u = 170mV which is close to the measured 165mV measured offset. Thus the customer may either adjust the resistor divider to account for the offset or use the lower values of resistors so that the offset is lower. In the example of the datasheet and the EVM the offset would be: Voffset = 43.2 * 8.5u = 0.4mV. To reduce the potential impact of noise on the output lower resistance values may be desirable for the applicaiton instead of using the 20k ohm and 40k ohm range which is fairly weak biasing of the feedback circuit.

    I'm working with the team how to clarify this in the datasheet.

    Scott
  • 0 in reply to Scott Monroe
    Guru 11235 points

    Hi Scott-san

     Thank you for your support.

     I understood.

     Your information helped us a lot.

    Thanks,

    Shimizu