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Original question:

TPS40210-HT: TPS40210-HT COMP Pin

TPS40210-HT: TPS40210-HT COMP & FB Pin

Asier Portillo
Prodigy 90 points
Part Number: TPS40210-HT

Tool/software:

Hello team,

A few months ago I asked a question about the chip's COMP pin. Now I have several questions after taking my simulation to the lab and finding it's not working properly.

In the case of an isolated system, like mine, is the FB pin connected to ground? My system doesn't have an optocoupler for isolation; I use a transformer instead. In this case, should the FB pin also be grounded? And if so, how does the feedback signal get to regulate the duty cycle? Only from the COMP signal?

I used the Excel spreadsheet you sent me as a guide, but it's not entirely helpful because I don't use an optocoupler for isolation.

Thanks in advance,
Asier Portillo

  • 0
    TI__Mastermind 30160 points

    Hi Asier,

    Thanks for opening a new thread in e2e.

    If you use a transformer winding for the feedback, you do not need to ground the FB pin. You can connect the transformer rail with a voltage divider to FB and this will rail will be regulated. The actual output rail will then be regulated indirectly via the transformer coupling.

    You can still use the calculator for this case.
    Please set the feedback to "non-isolated" and consider the LOAD 1 winding as your auxiliary winding and LOAD 2 as your actual output winding.

    Here is a reference design of how the feedback circuit should look like:
    https://www.ti.com/tool/PMP30336

    Best regards,
    Niklas

  • 0 in reply to Niklas Schwarz
    Prodigy 90 points

    Hello Niklas,

    Ok, thanks you very much for the response. I will check it.

    Best regards,

    Asier

  • 0
    Prodigy 90 points

    Hello Niklas,

    I've been doing some testing.

    I isolate the flyback with a transformer, and then, using a voltage divider, I get the 700 mV needed for the chip's FB pin input. I've seen that the chip is properly powered, but I can't get the COMP pin to reach the minimum voltage for it to start sending the gate signal to the MOSFET (GDRV).

    Measuring the voltage on the COMP, I see it's 500 mV, and I can't get it to increase enough for the chip to start communicating.

    I've tried several configurations, but none of them work:
    - Connecting the COMP to the FB via a RC.
    - Leaving the COMP pin with a RC and connected to ground.
    - Using a transistor to initially power the COMP (forcing that output) from the BP pin.

    I look forward to your reply.
    Thanks again,
    Asier Portillo

  • 0 in reply to Asier Portillo
    TI__Mastermind 30160 points

    Hi Asier,

    Thanks for the update.
    Could you please provide me a schematic of your application?
    If you are not comfortable sharing this information on the open forum, feel free to use the private messaging feature.

    Best regards,
    Niklas