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Original question:

UC1825B-SP: Application Guide for Designing Buck Converter

UC1825B-SP: UC1825B-SP - Duty cycle control through external methods

Garrett Barbour
Prodigy 20 points
Part Number: UC1825B-SP
Other Parts Discussed in Thread: UC1843B-SP,

Hello,

I am considering the UC1843B-SP for a non-synchronous buck application. The issue I am having trouble resolving is direct duty cycle control through external means. I have found an application note that describes methods of "voltage mode control"; however, I am trying to identify a method to use an external DAC for example. The goal is to input a voltage range into the control loop to directly impact the output voltage. If there are examples or application notes detailing this, that would be helpful.

Thank you

  • 0
    TI__Mastermind 26305 points

    Hey Garrett,

    I don't have any application notes detailing how to do this.

    I've had people in the past do this by directly controlling voltage at the COMP pin.

    The voltage at the COMP pin will change the output duty cycle directly.

    I however, don't have anything saying what voltages = what duty cycle, as the voltage at CS will also need to be taken into account.

    If you hold the CS pin to a specified voltage, you can test forcing the COMP pin of the device to find the corresponding voltages.

    Thanks,

    Daniel

  • 0 in reply to Daniel Hartung
    Prodigy 20 points

    Daniel,

    Thank you for the response. We will look into testing the above. Do you have a recommended alternative that is more inline with the TI's intended use case, that also meets my above criteria?

    Thank you,

    Garrett 

  • 0 in reply to Garrett Barbour
    TI__Mastermind 26305 points

    Hey Garrett,

    As long as you are looking at space grade controllers, my best suggestion is UC1825B-SP and UC1843B-SP.

    The radiation updated versions of these controllers are our latest controllers.

    I do not have a suggestion that will make using the DAC easier unfortuantely.

    Thanks,

    Daniel