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UCC28070A: Programmable Peak Current Limit Threshold

Shinichi Yokota
Genius 9715 points
Part Number: UCC28070A

Hello,

UCC28070A's programmable peak current limit function (PKLMT) uses a signal voltage at CSA/CSB pins. Therefore, an output current when the peak current limit occurs may differ depending on the input voltage since a peak current that runs through a CT (i.e. external MOSFET) is not the same. For example, a signal voltage at CSA/CSB pins is different between the input voltage of 180 and 220 V, causing a different PKLMT threshold between them.

Is there a way to minimize the difference? Ideally, I want to have the same PKLMT threshold for the output current in the input voltage range from 180 to 220 V.

Best regards,
Shinichi Yokota

  • 0
    TI__Expert 6150 points

    Hello Shinichi,

    The PKLMT for the CSA and the CSB pins are independent from each other. So, if the PKLMT was reached for the CSA pin but not the CSB pin then only the GDA pin is affected. 

    Is your question asking if the PKLMT current threshold will be different with an input voltage of 180V vs. 220V? The PKLMT current threshold is determined by the resistor divider across Vref so the PKLMT current threshold should be the same for both input voltages.

    Regards,

    Jonathan Wong

  • 0 in reply to Jonathan Wong
    TI__Genius 9715 points

    Jonathan,

    Please let me rephrase my question.

    The PKLMT threshold is determined by external resistor divider in the circuit, and thus fixed. The peak current level is different depending on the input voltage even under the same output current condition. The peak current level at VIN = 220 V is lower than the one at VIN = 180 V. This means that the peak current limit at VIN = 220 V will occur at a higher output current level than at VIN = 180 V.

    My question is, is there a way for the PKLMT function to occur at the same output current level?

    Best regards,
    Shinichi Yokota

  • 0 in reply to Shinichi Yokota
    TI__Expert 6150 points

    Hello Shinichi,

    The PKLMT current is set for the worst possible case in the design. So, in a 180V to 220V system you will design for a PKLMT at 180V. The other components such as the inductors and MOSFETs should be designed with this PKLMT current in mind. This is common practice we have seen among customers. At higher voltages Kvff settings and multiplier reference current will itself be a power limit by adjusting internal gains.

    Regards,

    Jonathan Wong