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PMP22899: How to set the over current limit.

sathish kumar
Prodigy 20 points
Part Number: PMP22899
Other Parts Discussed in Thread: TL2842B

Hi,

How to set the current in PMP22899, 

Please share the design data of the same.

We are designing a DC-DC Converter for 120W, 12V 10A Output.

Regards,

Sathishkumar 

  • 0
    TI__Expert 6250 points

    Hi Sathishkumar, 

    I have reached out to the designer John, he will get back to you soon on a more detailed answer.

    The basic concept is that R5 (0.62 ohms) is used as the current sense resistor, so that get compared to the CS threshold and sets the peak current.

    On a side note, a non sync buck for 10A output is not the best choice. Have you considered an alternative topology?

    Thanks

    Robert 

  • 0
    TI__Intellectual 1380 points

    Hi Sathishkumar, 

    Robert is correct, the resistance R5 can be adjusted to change the current limit for this design. The datasheet for TL2842B mentions that the over-current threshold is roughly 1 V on the ISENSE pin. In my original design I was expecting 1.5 A peak, so a 0.62 Ohm resistor would have a current limit slightly above my maximum loading condition.

    For your design 10 A would be a lot for a non-synchronous buck to handle. This design operates in CCM with a duty cycle between 14-20% across the line input. Since you are conducting across the free-wheeling rectifier for more time a synchronous switch would be a preferred method if you stick with the buck topology.

    Alternatively, I would recommend changing to a LLC half-bridge topology. PMP9739 is a design that creates a 24 Vdc output from a 120 Vac input that is capable of 10 A loading. All of the design files are available for reference on the design page as well as a detailed test report. Let me know if you have any questions about this approach.

    Thanks,

    John