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LM5022: LM5022 OCP curve

Lewis Cheng (TDK)
Prodigy 80 points
Part Number: LM5022
Other Parts Discussed in Thread: LMP8646

Hi,

I have a question about LM5022 IC OCP curve.

The following graph is my current design sample OCP curve.

The problem is OCP occurred and the Vo drop but at the critical point Io is too big . 

So, how do i adjust the OCP curve slope?

I appreciate your great help in advance.

Best regards,

  • 0
    TI__Mastermind 21720 points
    Hi Lewis,

    The LM5022 limits the peak inductor current not the output current. The curve you are showing is the expected current limiting behavior. To get the accurate output current limiting you will need to sense the output current and then use that to pull COMP down or increase the FB pin when the output current is too large. This can be done with a current sense amplifier, current sense resistor and an error amplifier. The LMP8646 is also another option that combines all these functions.

    -Garrett
  • 0 in reply to Garrett Roecker
    Prodigy 80 points

    Hi Garrett,

    Thank you for your prompt reply,

    Current design is an isolated flyback converter , so the FB pin is grounding , it's useless.

    And i already try to sense the Comp pin to limit output current , but the OCP curve is directly pull to zero and hiccup.

    Our customer request OCP curve is Vo drop and recovery , do you have any idea about this ?

    OCP SPEC request

    Lewis,

  • 0 in reply to Lewis Cheng (TDK)
    TI__Guru* 78200 points
    You can use the scheme to directly monitor the output current to attack the isolated feedback signal on the secondary side.