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UCC21225A: output has no change

Given Ding
Genius 10165 points
Part Number: UCC21225A

Hi Team,

Here is a question from customer. 

When there is PWM on INA/INB, OUTA and OUTB keep high and no change. 

In customer's application,

pin4 is connected to 3.3V, pin7 is floating.  Is it OK?  pin4 and pin7 are connected internally, so it seems OK. 

DISABLE is connected to GND, DT is floating,  is it OK? From datasheet, it seems OK. 

VDDA is 120V, VSSA is 110V, VDDB is 12V, VSSB is GND.   

Please kindly add your comments on possible reasons. Thanks. 

BRs

Given

  • 0
    TI__Guru**** 189401 points

    Hi, Given,

    Sorry you guys are having problems here.

    While pin 4 and 7 are internally connected, we do require them to be connected externally as well.

    Your disable connection is fine, and we also recommend adding a 2.2 nF or larger capacitor to the DT pin to ground as a noise filter.

    The above are all best practices, and I don't believe any of them are the root cause of your problem. I am especially perplexed by your statement that the outputs are always high.

    Please send me the schematic and any other information you have via email. I will close this thread and follow-up with you via email.