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UC2525A: Shutdown Levels Understanding

SIDDHESH KALA
Prodigy 40 points
Part Number: UC2525A

Tool/software:

I want to understand the Shutdown capability of the IC UC2525A. When does the IC go into shutdown mode, at what voltage levels? and are there any other circumstances that can trigger a false shutdown.

  • 0
    TI__Intellectual 790 points

    Hi Siddhesh,

    When shutdown pin is held high above the threshold, the PWM latch is reset and both OUTPUT A and OTPUTB turn off. If it is held high for a long time, it forces the soft-start capacitor to discharge.

    The threshold range is 0.6 V to 1 V.

    Any noise signal can trigger shutdown. Hence, using a strong RC filter near the SHUTDOWN pin is recommended.

     Please let me know if you have further questions. if you feel that I answered your question, please click on the "this resolved my issue button".

    Thank you.

    Best,

    Adhvaidh

  • 0 in reply to Adhvaidh Aravind
    Prodigy 40 points

    Everything is now clear, but can you also explain this:
    The compensation and soft start pins are also able to shutdown the IC, could you explain that as well?

  • +1 in reply to SIDDHESH KALA
    TI__Intellectual 790 points

    Soft start pin is a capacitor node driven internally. The voltage at this pin is the voltage across the capacitor. Initially, the capacitor is charged by the internal current source. Only when the shutdown pin is set, the internal transistor turns on, and the soft start capacitor will discharge through the transistor, and the voltage eventually goes down to zero. This discharge is not quick as the voltage across capacitor cannot change instantaneously (unlike shutdown pin). 

    Now, answering your question: when COMPENSATION and SOFTSTART pins are set to zero, it does not truly shut down the IC. Only the duty ratio goes to zero. Whereas, the shutdown pin truly shuts down the IC (PWM will not generate output, regardless of voltage at COMPENSATION pin). Please let me know if you further questions.

    Best,

    Adhvaidh