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Original question:

UCC28070: About Cuurent Sense

UCC28070: About Current Sense Resistor.

Martin Chien
Expert 3590 points
Part Number: UCC28070

Hello Team,

My customer intend to use current sense resistor instead of CT.

1. Should customer place Rsense at HV FET source pin to gnd, is that correct?

2. In order to reduce power losses, low Ohmic Rsense is preferred to use, thus lower scale input to CSA/CSB is expected and PKLIM pin would be set at lower level such as 1V or 0.5V, can they do that? is there any potential risk of setting lower PKLIM and CSA/CSB such as 0.5V~1V rather than 3V~3.5V?

Thanks,

Martin

  • 0
    TI__Mastermind 34465 points

    1401.Sch.PDFHello Martin,

    Some customers have designed in the UCC28070 with a resistive current sensing method.

    The resistor is placed on the source lead of the FETs and a high speed OPAMP is used to amplify the signal.

    Attached is a schematic that shows how the UCC28070 EVM is modified for resistive current sensing

    The OPAMP is required to amplify the low voltage sensed signal. Without the OPAMP it will be very difficult to accurately sense the FET current in the presence of switching noise and this will lead to poor performance of the pfc. 

    Regards

    John

  • 0 in reply to John Griffin1
    TI__Expert 3590 points
    Hello John,
    Is it possible to add external RC filter to reduce switching noise? have you ever try that? how's the performance looks like? OPAMP needs more space and cost is not preferred.
    Thanks,
    Martin
  • 0 in reply to Martin Chien
    TI__Mastermind 34465 points
    Hello Martin,
    This question has been answered in another post so I will close out this thread.
    Please open a new thread if you need further help.
    Regards
    John