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LM5146-Q1: Can Comp Pin Be Driven Directly?

Don Cutler
Prodigy 30 points
Part Number: LM5146-Q1
Other Parts Discussed in Thread: LM5146, LM5117-Q1

Hi,

Please see attached preliminary PDF schematic which shows one of two Buck Converters. 

I am trying to use two LM5146 as variable current sources using local output shunts to create the voltage feedback. The shunt output is fed back to an error amp with a variable reference to provide a variable setpoint. 

The question is can the LM5146 "comp" pin be driven directly to produce the signal to the PWM generator and bypass the internal error amp? If not, is there a more suitable chip? I was considering using another amplifier to provide offset and gain to drive the internal amplifier, but would rather not.

Thanks for the help.

Don

  • 0
    TI__Guru 65247 points

    Hi Don,

    Take a look at the LM5117-Q1 as this is more suitable for constant-current (CC) type loads. It has a convenient CM (current monitor) pin that facilitates CC mode configuration. Overdriving the COMP pin of the LM5146 is not really recommended.

    Regards,

    Tim

  • 0 in reply to Timothy Hegarty
    Prodigy 30 points

    Hi Tim

    Thanks for the quick response, although it wasn't the answer I was hoping for ;-)

    I'll look into the LM5117-Q1. However in the meantime, I have a PCBA in house and doing more development work with it for the short term until we update the board.

    Can you look into your crystal ball and tell me if I over drive the comp pin while looking at other issues, will it quickly kill the chip, or just degrade over time?

    I know this is an impossible question, but wondering if I can get some short term answers on the initial prototype.

    Thanks again for the help!

    Don

  • 0 in reply to Don Cutler
    TI__Guru 65247 points

    Don, it should be possible to overdrive COMP. The error amp has a drive capability of a few mA's.

    Another option is to inject on FB. Take a look at app note snva829.

    Tim