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TPS54560: TPS54560QDDA: Feedback network Resistor Values

Narasimha LV
Prodigy 130 points
Part Number: TPS54560

Hello,

for DMS project we are using TPS54560 part for DC-DC converter to generate 4V.

As per datasheet "Due to the input current of the FB pin, the current flowing through the feedback network should be greater than 1 μA to maintain the output voltage accuracy. Choosing higher resistor values decreases quiescent current and improves efficiency at low output currents but may also introduce noise immunity problems".

Due to our WCCA analysis, we wanted to use 1K and 3.9K resistors for feedback network. please let us know anything will affect on performance or efficiency? Higher resistor means what would be the minimum resistor values we can choose?

Please advise.

Regards,

Narasimha LV

  • 0
    TI__Guru**** 191445 points

    For a typical 5 V output, 1 uA will result in 5,000,000 ohm series resistance (5 uW loss).  When I design with these parts I typically use resistance values based on 10 k ohm bottom resistor (datasheet example uses 10.2 k ohm lower, 53.6 k ohm upper for 392 uW loss ).  Assuming your design is for 1.00 V, not 3.92 V design would dissipate 204 uW.  I would not find that to be excessive.  You should not have issues with those values. 

  • 0 in reply to JohnTucker
    Prodigy 130 points
    Hi John,

    Thanks for the response.
    with 1K and 3.9K the output voltage is 3.9V typical in our case. will it impact in efficiency?

    Regards,
    Narasimha LV
  • 0 in reply to Narasimha LV
    TI__Guru**** 191445 points
    Well, I guessed wrong I calculated both possible output voltages and picked the one closest to a standard value. The new dissipation is 3.14 mW, about 10x what you would get from 10 k and 39 k. Probably a small portion of the total power losses.