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UC1843B-SP: Slope Compensation

Part Number: UC1843B-SP

Hello,

I will be using UC1843B-SP in current-mode control for an inverting buck-boost. Can you provide guidance on how to calculate the appropriate value for Rramp for slope compensation?

Thank you,

Fernando

  • Hey Fernando,

    The minimum slope to add will be equal to the negative slope of the inductor current.
    Simply calculate that and use it in place for Sc in equations 46-51 in the datasheet.

    Thanks,
    Daniel

  • Hi Daniel,

    Since I will be using this controller in a inverting buck-boost topology, the inductor down-slope will be (Vout*R[current sense resistor])/Inductance. I let the Nps = 1 as a transformer is not being used. Am I on the right track?

    Thank you,

    Fernando

  • Hey Fernando,

    You are on the right track, but I do question how you have implemented the current sensing.
    Since the UC1843B-SP's current sense is referenced to ground and an IBB senses the high side current, there must be some circuitry you are using for that sensing.

    Most current sensing methods have some gain to them, so make sure that is being taken into account.

    Thanks,
    Daniel