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REG103-A output problems

Joe Ten
Prodigy 50 points
Other Parts Discussed in Thread: TPS74401, REG103

Hi All,

We have implemented a DC PCB using REG103-A regulators. Everything is going fine, except for the output of the REG-103A, which is 3.7V instead of the 5.3V we are expecting according to adjustable resistors values. Please find attached our circuit design.

A_VBIAS and D_VBIAS outputs of REG103-A are given 3.7V instead of the expected 5.3V.

Do you envisage any problem with this design?

Thanks in advance!

Regards,

Jose

  • 0
    TI__Mastermind 45250 points

    Jose,

    Please describe the load and the input voltage/ current to the REG103A.

    The resistor values etc. seem to be fine, so there must be an issue either with the load or with the input current to the device.

    Please let me know if you have further questions.

    Richard Elmquist

  • 0 in reply to Richard Elmquist
    Prodigy 50 points

    Richard,

    Input voltage is 15V from an external power supply. Load is the TPS74401 BIAS inputs shown in the previously attached picture.

    Thanks,

    Jose

  • 0 in reply to Joe Ten
    TI__Mastermind 45250 points

    Jose,

    The TPS74401’s show input voltages of 3.3V and 1.8V. The output of the REG103 was specified to be 5.3V.

    Are the inputs to the TPS74401’s 5.3V? What are the output loads associated with each these supplies? Are each of the TPS7440’s supplied by one of the REG103’s?

    Also let me know more about the 15V supply. What is its current rating and does it supply just this circuit?

    Please let me know if you have any additional questions.

    Richard Elmquist

  • 0 in reply to Richard Elmquist
    Prodigy 50 points

    Richard,

    The output of the REG103 (5.3V) is the input of the TPS74401’s BIAS input. As you mention, the Vin input are 3.3V and 1.8V respectevily. Each REG103 supplies the BIAS input of three TPS74401. Load of TPS74401 supplies are standard ICs (ADC, DAC, FPGA,...).

    For testing, we are trying 15V from a laboratory DC suppl, supplying only this circuit. 

    Summarising, we are using REG103 to feed BIAS input of TPS74401. Is this is a correct approach?

    Thanks and regards,

    Jose

  • 0 in reply to Joe Ten
    TI__Mastermind 45250 points

    Jose,

    There should be no issue in using the REG103 to supply the bias voltage to the TPS74401. The TPS74401 specs the maximum current draw on each of the bias pins to be 4mA so the maximum current would be 12mA.This is well below the maximum current level of the REG103.

    Are the TPS74401's working properly when you see this issue with the REG103? Do each of the REG103's work properly if not connected to the BIAS pin of the TPS74401? Do they work properly if the TPS74401's are not enabled?

    It seems to me that there must be a short somewhere is the circuit that is bleeding current causing the output voltage from the REG103 to be pulled down.

    Please let me know if you have any further questions.

    Richard Elmquist

     

  • 0 in reply to Richard Elmquist
    Prodigy 50 points

    Richard,

    I think you are write. One of the TPS was broken, causing a short-like effect.

    Thanks for the support and regards,

    Jose

  • 0 in reply to Joe Ten
    TI__Mastermind 45250 points

    Jose,

    I am glad that I could help and that you were able to isolate and fix the issue!

    Richard Elmquist