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TL594: Treatment of PWM signal to the Feedback pin

Shinichi Inoue
Guru 21861 points
Part Number: TL594


Dear Specialists,

My customer is considering  PWM signal to the Feedback pin and error amplifier does not use.

Could you please provide the reference design or circuit example.

I think it is necessary to convert the PWM signal to DC with a CR filter.

Also could you please let us know the pin configuration when the error amplifier is not used

I appreciate your great help in advance.

Best regards,

Shinichi

  • +1
    TI__Mastermind 33115 points

    Shinichi,

    If driving the FB pin directly, a DC signal representing the voltage error between the measured control signal (divided down output voltage) and voltage reference should be applied to FB. the unused amplifiers should be configured so that their output is driven LOW so that the amplifier outputs are off. Your question has been posed before and you can see the schematic configuration in this E2E thread. Similar situation applies if only one amplifier is used and one is to be disabled and this situation has also been addressed in this E2E thread. Thanks for connecting through E2E.

    Regards,

    Steve M

  • 0 in reply to Steven Mappus1
    Guru 21861 points

    HI Steven,

    Thank you for your reply.

    I'll share your answer with the customer.

    The customer has an additional question, could you please let us know.

    Is there any problem with inputting the PWM signal through the RC filter to the FB pin?

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi

  • +1 in reply to Shinichi Inoue
    TI__Mastermind 33115 points

    Shinichi,

    Electrically there is no problem to do this but if you are designing a closed loop power converter, the performance of the will not be good. The transient response and regulation will suffer when you add such a large RC time constant to the FB. 

    Regards,

    Steve M

  • 0 in reply to Steven Mappus1
    Guru 21861 points

    Hi Steve,

    Thank you for your reply.

    I shared this your answer with the customer.

    I appreciate your great help and cooperation.

    Best regards,

    Shinichi