Tool/software:
Dear TI Support Team,
I am currently working with the UCC28740-Q1 in my application and have encountered an issue. I applied 24V to the VDD pin of the IC, but I observed that there is no PWM signal output.
Could you kindly help me confirm if there might be an issue with my circuit design, or if there are any additional factors I should check to resolve this problem?
Thanks!
Hello,
The UCC28740 on initial startup will give three sample pulses to check for over current, input under voltage and over voltage. If any of these faults are triggered switching will stop and require VDD to cycle between VDD(on), VDD(off) to VDD(on) to reset the fault.
In your case since you only applied VDD the device gave three gate driver pulses and shut down do to input under voltage. Becuase you have VDD stet to 24 V the chip will not reset.
The UCC28740 uses primary fault sensing. The following will bring you to an application note that discusses primary fault sensing and the issues with it and how to resolve them. I would read through this before conituing your design to avoid possible problems. In this application note section 4 describes the issue your seeing. In this case appling enough input voltage to your design will aviode the input under voltage fault.
https://www.ti.com/lit/pdf/sluaac5
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