UCC28631: DRV signal does not appear

Hi Leandro,

Thanks for your interest in UCC28631. Does the VDD pin reach ~14.75V? If yes, do you see any exploratory pulses? Do you see VDD settle to a DC voltage or does it oscillate?

Best Regards,
Ben Lough

Hello Ben,

The Vdd reachs 14,7V once and then keep oscilating between 8 and 11V approximately.

I see no exploratory pulses.

Best regards,

Leandro

Hi Leandro,

It sounds like the controller is entering a latched fault mode. Could you probe the SD pin and check for pulses at startup?

Best Regards,
Ben Lough

Hello Ben,

The SD pin shows pulses indeed.

Hi Leandro,

Thank you for the waveform. 23 pulses indicates the controller is detecting a CS pin fault. Could you check to see if the CS pin is either open or shorted to gnd?

Best Regards,
Ben Lough

Hello Ben,

My CS pin is not grounded nor open. It's like the schematics:

Leandro,

The controller itself is detecting a fault with the CS pin. Could you check if the CS pin is soldered down incorrectly?

Best Regards,
Ben Lough

Hello Ben,

There was a soldering fault, it worked but I was limiting the current because I had 3 MOSFETS burned. When I took off the resistor, my MOSFET burned again, the mosfet and the series resistor on the gate of mosfet. Could it be the switching frequency?

Best regards

Hi Leandro,

This controller uses a mix of peak current mode control and frequency modulation so the current sense resistor is needed. When the resistor was installed, could you tell me what you were observing? It's possible you were seeing the exploratory pulses and perhaps the controller is sensing line UV. Can you tell me the behavior of VDD with the resistor installed?

Best Regards,
Ben Lough

Hello Ben,

Actually the resistor I said earlier was a resistor on the AC power, to limit the maximum current on the whole circuit. Without load, the circuit worked with this AC current limitator. When I took it off, the MOSFET burned.

When it was working, the VDD was like that:

I have also the curves on DRV pin:

Best regards

Hi Leandro,

I would recommend using a NTC to limit the current inrush. The first image you showed is the controller detecting the AC line is below the AC-ON threshold. If you see this, try raising the input voltage to see if the converter starts up.

Best Regards,
Ben Lough

Hello Ben,

I am using a EE40 Core, I am using this table to calculate the component's values, could you check if it's right for me?

excel table: https://wetransfer.com/downloads/841a9ab42a1d22cae1c4a146ac44990a20180824132203/a23fedea986e9fb56e8f5bb1431daccb20180824132203/d5124b

Best regards

Hi Leandro,

I'm not able to open the file but I would recommend using the UCC2863x calculator to determine your component values. You can find the calculator at the bottom of this page: www.ti.com/.../toolssoftware

Best Regards,
Ben Lough

Hello Ben,

Again I started the circuit with a current limit. The UCC28631 started, the VDD rised and stabilized on 10~11V. I checked the DRV signal, there was a 1,7V amplitude signal with aproximately 1KHz. On th SD pin there was this signal:

The DRV signal could not activate the MOSFET, so there was no 12VDC output. What could it be this low amplitude DRV signal?

Best regards

Hi Leandro,

DRV derives its power from VDD. If the gate is only being driven to 1.7V max, the controller may have been damaged. Please try replacing the IC and see if this behavior persists.

Best Regards,
Ben Lough

Hi Leandro,

Were you able to replace the IC and retest?

Best Regards,
Ben Lough