UCC5350: UCC5350 output not pulling close to VCC2

Ikenna Chukwuka

Part Number: UCC5350

Hello,

I need some help here and this is not the first time I am asking about this device. As shown in the diagram, I am supplying the VCC1 and IN+ with 5V and the VCC2 with 20V. VEE2 with -5V. Ignore the -3V.

When I probe the output, I am expecting the output to pull close to VCC2, but why am I getting 3.2V at VCC2 pin.5 and the output? I have looked at my circuit; there is no missing track or wrong connection, but I still do not understand why I am 3.2V.

Please advise on what to do here.

Regards,

over 2 years ago

0 Don Dapkus over 2 years ago

TI__Guru**** 189399 points

Hi, Ikenna,

Sorry you are having difficulty here.

What is the value of R2? What load are you driving?

Try shorting out R2 and disconnecting your load to see if you get 20V as expected, and let me know what you see.

Best regards,

Don

0 Ikenna Chukwuka over 2 years ago in reply to Don Dapkus

Prodigy 185 points

Hello Don,

For now, the value of R2 is 1 ohm, since I am not driving it with any load. It is meant to drive a SIC MOSFET for me, but I have to make sure I am getting the right voltage at the output before using it to drive my SIC Mosfet.

Even with R2 shorted out, it is now pulling VCC2 to 3.2V.

Regards,

0 Ikenna Chukwuka over 2 years ago in reply to Don Dapkus

Prodigy 185 points

I know that both input and output are isolated from each other. If I am probing the output, what do I probe the output in reference with? VEE2?

0 Don Dapkus over 2 years ago in reply to Ikenna Chukwuka

TI__Guru**** 189399 points

Hi, Ikenna,

Yes. Is that where you are probing with respect to?

Best regards,

Don

0 Ikenna Chukwuka over 2 years ago in reply to Don Dapkus

Prodigy 185 points

Hello Don,

So I short R2 and I can measure 20V at VCC2, but the issue is I am having now is that at the output I am getting 3.2V. If I measure the output with reference to PGND, I am getting 3.2V. Is there anywhere on the schematic I can measure the output (Pin.6) in reference to?

0 Ikenna Chukwuka over 2 years ago in reply to Ikenna Chukwuka

Prodigy 185 points

I should be able to see a 0V if I measure output (Pin.6) in relation to VCC2 (Pin.5), but my measurements show 20V and -20V.

0 Don Dapkus over 2 years ago in reply to Ikenna Chukwuka

TI__Guru**** 189399 points

Hi, Ikenna,

If the output isn't equal to VCC2 and VEE2, then you most likely have a short somewhere on your board.

Best regards,

Don

0 Ikenna Chukwuka over 2 years ago in reply to Don Dapkus

Prodigy 185 points

I am getting 20V at VCC2 and -3.5V at VEE2. I do not understand why still the output not pulling close to VCC2.

Regards,

0 Ikenna Chukwuka over 2 years ago in reply to Don Dapkus

Prodigy 185 points

I use reference TP5 with reference, which is derived from my isolator, to probe VCC2. I am getting 20V and if I probe it with reference to VEE2 I am getting -3.5V, but when I probe it with reference to the output it gives me -3.5V. It's like it is pulling down to VEE2.

I have checked the layout and there is nothing like a missing track or wrong connection, but I still do not understand why it is not going up enough to 20V but rather 3.5V.

Regards,

0 Don Dapkus over 2 years ago in reply to Ikenna Chukwuka

TI__Guru**** 189399 points

Hi, Ikenna,

Is your input signal within specification? This IC requires an input signal to be >0.7*VCC1 in order to recognize a high input condition.

If your input logic voltage is within specification, can you send a bit more of your schematic? I’d like to see how you have your power device connected to our driver

Best regards,

Don

0 Don Dapkus over 2 years ago in reply to Don Dapkus

TI__Guru**** 189399 points

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/967877/faq-ucc5310-logic-input-characteristics-of-ucc53xx-family

this is an FAQ that discusses the input logic thresholds.

Best regards,

Don

0 Ikenna Chukwuka over 2 years ago in reply to Don Dapkus

Prodigy 185 points

Hello Don,

Thanks, I have been able to resolve the issue.

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UCC5350: UCC5350 output not pulling close to VCC2