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TPS5410: About Vout tolerance between feedback resistors

Michael Jeong1
Expert 2630 points
Part Number: TPS5410

Hello Expert,

Our customer has a symptom that there is Vout drift issue between feedback resistors.

Below is my questions.

Could you please reply to my each question?

1. When I checked recommended Rfbt resistor on the data sheet and WEBENCH, it is 10kohm.

    If I use Rfbt 1kohm and Rfbb 323ohm, Is there no problem?

    (This your comment is very important to our customer)

    Our customer Vout set is 5V and Vin 24V.

    So they want to use Rfbt 1kohm and Rfbb 323ohm.

    Also, when I simulated w/ WEBENCH at above resistor values, there is no error.

    Reason why is the below my 2'nd question.

2. In condition of Rfbt 9.1kohm and Rfbb 2.94kohm, we measured that it is from 4.98V to 5.1V.

    In condition of Rfbt 1kohm and Rfbb 323ohm, we measured that it is from 4.98V to 5.02V.

    What's the reason to make this difference?

    They use this Vout to reference voltage of DAC.

    So, In condition of Rfbt 9.1kohm and Rfbb 2.94kohm, there is issue which is to increase tolerance of DAC

 3. What's min/max the output voltage accuracy of this device from Tj -40 to Tj 125?

     I want to know whether it is spec. in or not In condition of Rfbt 9.1kohm and Rfbb 2.94kohm.

 4. It is schematic of our customer.

     When I checked, there is no problem.

     Could you please double check?

     

    

Thanks and Best regards,

Michael

  • 0
    TI__Guru 73235 points

    Hello

    I don't see any issue with the schematic.

    With the 9.1k resistor your total error spread is only 2.4%.

    With the 1k resistor you total error spread is only 0.8%

    These are both much less than the ensured specification of 4% for the reference alone.

    Keep in mind that the ensured specification is for the reference voltage only; not the output voltage.

    The block diagram of the TPS5410 shows some internal impedance connected to the VSNS input.

    This is probably causing some small current to flow in the feedback resistors, causing the small error difference.

    The second line in the EC table for the reference voltage is valid for -40C to 125C.

    Unless the customer is OK with at least a 4% total error in output voltage, they will not be able to use a voltage 

    regulator as a precision reference for a DAC.

    Thanks

  • 0 in reply to Frank De Stasi
    Expert 2630 points

    Hi Frank,

    Thanks for your quick response.

    Anyway, is there OK to use Rfbt 1kohm and Rfbb 323ohm?

    How come the tolerance is 4%?

    It is 1.96%

    BR,

    Michael

  • 0 in reply to Michael Jeong1
    TI__Guru 73235 points

    Hello

    Yes it is OK with 1k.

    It is +/1 2% or a total of 4%.

    Thanks