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TPS40057: Setting of phase compensation during sink operation

Kaji@PAN
Mastermind 7775 points
Part Number: TPS40057

Hi,

I am considering a sink circuit using TPS40057.
Operating condition = input 12 V ± 10%, output 2.5 V, output current -1 A (sink only)
Used as power supply for LCD Vcom.

The circuit constants are determined based on the calculation formula of the data sheet.
The phase compensation constant uses the attached Excel sheet.

I would like to ask one question about setting up an excel sheet.
There is "IOUT_max" in the item of the excel sheet.
In the case of sink only, should I input minus 1 A?
Should I enter plus 1A?

Best Regards,TPS40KType III Loop Stability kVenable_sluc263c-071312_test1_20171102.xls

  • 0
    TI__Mastermind 39980 points

    Hello,

    if you actually have a negative current then a negative current should be entered.  The current in a buck typically is positive, even at 0A load, you have a slight positive DC current flow to the output even though the FETs are sourcing and sinking currents though the buck inductor?  If a negative DC current flows, that means you are dumping energy into the input supply and the output voltage will typically fall.

    Hope this helps?

    David.

  • 0 in reply to David Baba
    Mastermind 7775 points

    Thank you for your reply.
    I am going to calculate with a negative 1A set.

    There are things I do not understand because of the advice.
    Have you pointed out that the following content is problematic only with sink operation?

    "If a negative DC current flows, that means you are dumping energy
     into the input supply and the output voltage will typically fall."

    Best Regards,

  • 0 in reply to Kaji@PAN
    TI__Mastermind 39980 points

    Very sorry, not sure what you mean?

    It may be easier is you take a measurement of the inductor current to help better describe your problem?

    Thanks in advance.

    David.

  • 0 in reply to David Baba
    Mastermind 7775 points
    I am going to purchase EVM and make measurements.
    However, is it not appropriate to only operate the sink in this device?
    Best Regards,