UCC27611: Problems turning on the GaN MOSFET

Alejandro Torres

Part Number: UCC27611

Hi.

I'm testing a PCB that acts like a braking resistor circuit (https://images.app.goo.gl/hzKZzQpF1cWaBLFaA). I'm using this low-side gate driver to switch the GaNFET EPC2215. I'm using a square signal waveform of 10kHz and 3.3V unipolar signal. But the output signal have a very strange waveform. I attach you the waveforms in the different pins:

Pin 1: VDD (12V)

Pin 3 (Non-inverting input):

Pin 6 (VREF):

Pin 5 (OUT):

As you can see, the switching at the output is wrong.

I'll attach you also the schematic capture of the driver and the MOSFET.

over 1 year ago

0 Rubas Khalid over 1 year ago

TI__Expert 6035 points

Hi Alejandro,

Looking at your schematic, I see that you do not have a bypass capacitor on the VREF pin. A bypass capacitor is required on that pin and placed as close as possible to the chip because the VREF pin supplies the charge for the current delivered by the OUTH pin. Whenever there's a current from OUTH, a corresponding pulse is delivered from VREF, so a bypass capacitor is required for decoupling purposes. Please let me know if more info is required.

Thanks,

Rubas

0 Alejandro Torres over 1 year ago

Prodigy 10 points

Hi Rubas.

Thanks for your fast answer.

As you said, the decoupling capacitor is placed but is not in the schematic. I've tested also with no gate resistor, and the results are the same.

0 Rubas Khalid over 1 year ago in reply to Alejandro Torres

TI__Expert 6035 points

Hi Alejandro,

What's the value of the capacitor? Can you also send a picture of the layout?

Thanks,

Rubas

0 Alejandro Torres over 1 year ago in reply to Rubas Khalid

Prodigy 10 points

Hi again.

The value of the capacitor is 100nF. It's not reflected in the schematic because it is added later.

I have attached the layout of this component.

0 Rubas Khalid over 1 year ago in reply to Alejandro Torres

TI__Expert 6035 points

I see that you have a different ground for the pad of the device. Try grounding everything to a common ground, and it should fix the problem. The bypass capacitor value is good, but you can experiment with 1uF as well. Make sure to place it as close as you can to the device.

Best,

Rubas

0 Alejandro Torres over 1 year ago

Prodigy 10 points

Hi again Rubas.

I've tried to connect at a nearer point to the grounds and it works well!

Thank you a lot.

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UCC27611: Problems turning on the GaN MOSFET