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LMP8646: How determine the bandwidth?

dao hop
Prodigy 160 points
Part Number: LMP8646
Other Parts Discussed in Thread: LM5143

Hi all,

I'm using LMP8646 in my design.

The parameters:

- Rsense: 5mR

- ILIM = 100A

- Vfb = 0.6V, Rg = 5.97k.

I meet some troube when calculate Cg. I don't know how to determine the bandwidth.

Could you help me and expain mor about this?

Regards

  • 0
    TI__Mastermind 26525 points

    Hello Dao, 

    The Cg will be application and converter you are using.  This bandwidth limits the feedback path to your converter from the limiter.  This is something you may need to change in your application.  If the application is similar to the example then I would start off with a similar bandwidth.  There are 2 examples in the datasheet.  The speed of your current limit is and stability with your converter are the main factors in picking the bandwidth.  Normally the bandwidth will be much lower than your switching frequency as you can see in the examples in the datasheet.

    Regards,

    Javier

  • 0 in reply to Javier Contreras4
    Prodigy 160 points

    Hello Javier,

    I'm using LMP8646 with LM5143: Vout = 11V, I = 100A.

    Could you give more advice to me?

  • 0 in reply to dao hop
    TI__Mastermind 26525 points

    Hello Dao,

    Like a said you need more information and testing in your application.  What is your switching frequency?  I would start with something like 1kHz but make sure you can move up and down with experiments for your application.  The whole application matters in your load, inductor, and FETs in your system.  This will be something you should confirm works in your application with everything as it would be in normal operation.

    As you can see all the applications mentioned in the datasheet had the bandwidth adjusted to find the correct bandwidth for each.  Place footprints on your PCB to be able to adjust the values of Rg and Cg.

    Regards,