UCC21732QDWEVM-025: About using transformer T1, T2 and more...

Hi Yoonjin, 

Interesting - there should be no problem doing that and feed in the secondary side power via the test points. If you're not using VEE, however, tie it to COM. 

Can you measure the VCC, VDD, and VEE at the gate driver pins to make sure they are at the desired voltage? Also can you elaborate on the problem that the gate driver has? 

Thanks, 

Vivian

I unpopulated T1, T2 and U1, U2, U3 to feed in the secondary side power externally via the test points TP1, TP2, TP3. 

I am feeding TP4 (VCC=5V), TP6 (GND=0V), TP2 & TP3 (COM=VEE=0V), TP1(VDD=15V), and IN+(5V PWM J2:12) , IN-(J2:10 at 0V)

I measured the VCC, VDD and VEE and they were at the desired voltage.

The problem is that when I probe GATE pin, output waveform is just at ground signal. 

and also LED(RDY) doesn't illuminate while LED(FLT bar) is illuminating.

I also measured RDY pin, and it was 30mV (desired voltage = 1.8V right?)

+

It happened same on UCC21710 Evaluation board, and this time I didn't unpopulated anything.

I just give power to TP5 (5V) GND to J2:11 and measured VDD, VEE, COM on secondary side. 

and suddenly the LED(D11) become darker. and RDY pin doesn't output desired voltage again.

I want to know what my mistake is . thank you!

Hi YoonJin, 

Thank you for the additional information. Our expert is out of office today due to the US holiday and will get back to you in the next couple of days. 

Best regards,

Leslie

Hi YoonJin, 

I saw you posted another thread on a similar issue with the UCC21710 evaluation board. I recommend doing the same thing - measure the VCC and VDD with the oscilloscope first to make sure there's no excessive noise on these pins and we can diagnose from there. 

And to understand this better - the 21732 EVM would not power up at all, while the 21710 EVM powered up and worked normally for a period of time before the output was lost and RDY pin is pulled down? 

Thanks, 

Vivian

Thank you Vivian.

For 21732 EVM, I unpopulated T1, T2, U1, U2, U3 to use power supply on VDD, VEE, COM on secondary side.

For 21710 EVM, I didn't modify anything.

And these two are operating same.

First time, both two operated normally (output exist), but now outputs are lost and RDY pins are pulled down on 21710 and 21732 all.

Thanks,

Yoonjin.

+) I probed the both input signal(+)-GND(-) and output signal(+)-COM(-) using same oscilloscope at the same time to measure propagation delay. 

Could this have been a problem? I thought the ground in the oscilloscope was tied to each other channel. and I guressed it might have damaged the chip by tying GND and COM. I'm not sure but it seems that the pulled down RDY and output loss occured after measuring the prop. delay.

Hi YoonJin, 

Probing both sides simultaneously should not be a problem; we perform these type of tests frequently and the oscilloscope we use also has grounds tied to each other. 

Are the gate drivers damaged? Does it function normally after you power cycle the board? 

Thanks, 

Vivian

If the power cycle means the reset procedure for Power VCC and GND, no,the board would still not function normally when it is powered off and on again.

I guessed the gate drivers are damaged, because the RDY pins are pulled down with 5V VCC Power and current increased to 0.1A (displayed on VCC Power Supply).

If not because of the oscilloscope measurement, the other test I conducted at that stage was to measure the voltage between VDD, VEE, and COM of secondary side using a digital multimeter while giving VCC. Is there a situation that is supposed to be a problem here?