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UCC28881: Regulation performance at light load for 5V output

Oba
Genius 17335 points
Part Number: UCC28881

Hello,

My customer is interested in UCC28881 and have a question.
According to Figure 17 on the datasheet(SLUSC36B), the output voltage increase at the light load and this graph shows 12V output case.
They would like to know 5V output case. Do you have the same graph for 5V output case?

And 9.2.1.2.7 explains this no-load regulation performance highly depends on the time constant configuration.
Do you have any data about how much regulation performance can be realized at 5V output case?

They want to connect a LDO to this UCC28881 output and they have to know the max input voltage of this LDO.

Regards,
Oba

  • 0
    TI__Expert 7080 points

    Hi Oba,

    The light load /no load regulation not only impacted by time constant on FB pin, but also by Pre-load resistor and if any Zener on output side.

    Datasheet also mentioned that the time constant also will influence heavier load regulation . so trade off should be made between light load and heavy load . that is a  system level balance design spec.  my recommendation is tested it based on experiments. but you can refer to Figure 17 for roughly estimate the regulation at 5V.

    Thanks.

  • 0 in reply to Jaden Ning
    TI__Genius 17335 points

    Hello,

    Thank you very much for your reply.
    I tried to understand the reason of increasing VOUT voltage at the light load by Pspice simulation, but I couldn't understand.
    Do you have any document or something to explain it?

    Regards,
    Oba

  • 0 in reply to Oba
    TI__Expert 7080 points

    Hi Oba,

    Sorry that I don't find any document to explain it.

    UCC28881 operates at on/off control. PWM on/off decided by FB pin voltage . at light load . the high side buck converter operates with a fixed minimum switching frequency , while there is little load to discharge the voltage on output capacitor . that is why Vout increasing at light load.

    Thanks.