UCC28810: Design issues

Hi Mohitha,

Could you verify pin 4 if D17 is connected to primary ground? In the schematic, it looks to be floating.

Best Regards,
Ben Lough

Hi sir, 

Sorry for late reply. I verified the Pin 4 of D17 is connected to primary ground. However there is an issue that VDD pin without connection is 18V. But as soon as the IC is connected the voltage becomes 13V. And the output at the Gdrv pin is not triggering the external Power Mosfet. What is the voltage range that should be in GDRV pin? Current is less than or equal to 750mA(from datasheet). Please help. Thank you in advance.

Regards

Mohitha

Hi Mohitha,

Could you clarify "VDD pin without connection is 18V"? Are you saying when the VDD pin is left floating you are measuring 18V on the pin? If the device is sinking 750mA and there is no switching action the device might be damaged. If you replace the IC, do you the same behavior?

Best Regards,
Ben Lough

Hi sir,

I mean without connecting ic it is 18v ic but once I connect ic voltage drop occurs from 18v to 13v. I changed ic and checked.  Same issue persist.  Is it because of the circuit between gdrv pin and gate of external mosfet?  Is that part necessary or can we connect directly is gdrv to power mosfet.?

Hi Mohitha,

Could you check the voltage on the VSENSE pin? It should be 2.5V. If the pin is pulled to gnd, the controller will be disabled.

Could you also double check the connection of Q1 drain? It looks like it is connected directly to the rectified input voltage. It should be connected to T1 and the anode of D1.

Best Regards,
Ben Lough

0116.Schematic_ucc28810_Sheet-1_20190503174412.pdf

Hi sir,

I checked vsense pin. It was working fine. I modified the circuit as you said but the resistor R11 got burned. It was 2 watts resistor. Another time schottky diode D8 got burned.  Why is it happeningg? The circuit at the output given to EAOUT pin has any problems? should i give any protection?can you suggest some protection?Thank you in advance

Hi Mohitha,

Are you able to share a copy of your layout?

Best Regards,
Ben Lough

Hi sir,

I have attached a pdf file in the last post. Kindly find it.

Hi sir,  

Can you help me find the number of turns,  currents it support and core area of transformer T1 used in Pmp4862.  

Hi Mohitha,

I have asked the designer of PMP4862 for details on the transformer spec. I will send the datasheet to you once I have a copy.

Best Regards,
Ben Lough

Hi Mohitha,

After looking at your schematic again, I would suggest replacing D8 with a 0Ω resistor. D8 would prevent the controller from turning off the FET. Also please replace C15 with a short. This is to give you type II compensation. Please remove D10 as well.

Best Regards,
Ben Lough