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UCC21225A: UCC21225 is not synchronous with input signal from DSP

Ernest Yong
Intellectual 1510 points
Part Number: UCC21225A

Hi Team,

When my customer tried to power up with output load, it shows that the output signal of UCC21225 is not synchronous with input-signal DSP.

Please see this reference below:

I hope to hear from you soon, thank you.

  • 0
    TI__Intellectual 1795 points

    Hi Ernest,

    Sorry to hear that your customer is having trouble. From looking at your schematic I believe the issue may be with deadtime pin. It needs to be tied to  the Rdt resistor which determines the deadtime and between 500 Ohms and 500K Ohms. There are more specific schematic guides in the datasheet starting from page 25. Datasheet - https://www.ti.com/product/UCC21225A.

    Please let me know if you are still having issues.

    Regards,

    Akshat Murali

  • 0 in reply to Akshat Murali
    TI__Intellectual 1510 points

    Hi Akshat,

    Thanks for sharing. I went through the data sheet and it stated that DT pin can be opened or place a resistor. It is recommended to place a 2.2nF parallel ceramic capacitor with DT pin (which is what my customer did).

    May I check with you how is putting a 2.2nF capacitor different from open? 

    Thanks.

  • +1 in reply to Ernest Yong
    TI__Intellectual 1795 points

    Hi Ernest,

    The DT resistor vale determines the dead time though this formula - tDT(ns)=10×RDT(kΩ). If you are using deadtime you must connect it to the resistor and if the DT value is large, the 2.2nF capacitor is placed in parallel for noise immunity. 

    If dead time is not required and overlapping the outputs is allowed, DT should be connected to VCCI to disable the dead time feature. Connecting the pin straight to capacitor (like it was done in the schematic previously) makes it act as it is floating and external noise can couple into the pin aand affect the behavior of the output. Hope this answers your question!

    Regards,

    Akshat Murali