UCC28742: No Driver Signal

Ying Huang2

Part Number: UCC28742

This is my schematic. I'd like to generate a 120 V dc output voltage and one around 10 V dc output voltage. With 110 AC, 50 Hz input, VDD pin of UC28742 has a Sawtooth Wave (lowest value around 8 V, highest value around 21 V, frequency around 23 kHz). However, the DRV pin of UC28742 has no output. Is anybody has an idea about this issue?

Thank you for your help.

Best regards,

Ying

over 6 years ago

0 Ying Huang2 over 6 years ago

Prodigy 50 points

Sorry, the frequency of the Sawtooth wave in VDD pin is around 23 Hz, not 23 kHz.

0 Hong Huang over 6 years ago in reply to Ying Huang2

TI__Guru 73595 points

When VDD reaches its threshold to turn on, about 21V, you should see DRV at least a pulse, and CS following to have same number of pulses. If you don't see any pulse on DRV, your circuit connections have something wrong, or some damages.

I suggest you get an EVM so help you to know how the IC works.

0 Ying Huang2 over 6 years ago in reply to Hong Huang

Prodigy 50 points

Thank you for your reply. I have a question about VDD. Based on my design, if the converter work properly, VDD should maintain at around 16 V dc, which is below VDD turn-on threshold but above VDD turn-off threshold. In this way, can my converter start-up to work?

0 Ying Huang2 over 6 years ago in reply to Hong Huang

Prodigy 50 points

0 Hong Huang over 6 years ago in reply to Ying Huang2

TI__Guru 73595 points

You have to see DRV shows pulse when VDD reaches its turn on threshold. If you don't see DRV pulse when VDD reaches its turn-on threshold, there are connection issues or something damaged, you won't see the converter to work.

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UCC28742: No Driver Signal