UCC28911: issue of PMP10676

Hely Zhang

Intellectual 1160 points

Part Number: UCC28911
Other Parts Discussed in Thread: PMP10767

Looks like pin map of UCC28911 is wrong on schematic of PMP10676, pin 6 should be VDD while pin 5 should be VS, right?

Thanks

Hely

over 3 years ago

0 Mike O' over 3 years ago

TI__Guru* 86286 points

Hello,

Could you send me a link to this reference design? I cannot find it on TI.com

Regards,

Mike

0 Hely Zhang over 3 years ago in reply to Mike O'

TI__Intellectual 1160 points

Hi, Mike

Sorry , it's PMP10767. here it is:

https://www.ti.com/tool/PMP10767?keyMatch=&tisearch=search-everything&usecase=refdesign

Thanks

Hely

0 Mike O' over 3 years ago in reply to Hely Zhang

TI__Guru* 86286 points

Hello,

Thanks for letting us know. I will contact the designer so they can fixt it.

Regards,

0 Hely Zhang over 3 years ago in reply to Mike O'

TI__Intellectual 1160 points

Hi, Mike

Pls also let me know who is the designer, so i can ask some questions to him/her.

Thanks

Hely

0 Hely Zhang over 3 years ago in reply to Mike O'

TI__Intellectual 1160 points

Hi, Mike

Pls also let me know who is the designer, so i can ask some questions to him/her.

Thanks

Hely

0 Mike O' over 3 years ago in reply to Hely Zhang

TI__Guru* 86286 points

Hello Zhang,

The designer name is Sean and I have assigned the post to him so he can answer your questions directly.

Regards,

0 Hely Zhang over 3 years ago in reply to Mike O'

TI__Intellectual 1160 points

Thanks Mike, I will contact him.

0 Hely Zhang over 3 years ago in reply to Mike O'

TI__Intellectual 1160 points

Hi, Sean and Mike,

I am now designing a 15V/300mA high voltage buck with UCC28911, same topology as PMP10767, now it can only output 145mA at less than 80VDC input voltage, if I increase input voltage to >80VDC, then output voltage will drop, and keep dropping as I increasing input voltage.

For example, output will drop to 13VDC at 100ohm load resistor if input voltage is 100VDC.

BTW, i am using a 280uH inductor, not 1mH, inductor current is linear, not saturated, checked.

See below schematic and VS pin voltage(on R32) on channel 2( channel one is voltage on freewheel diode D23), VS is only 3.5V when output is 13VDC, so why UCC28911 does not increase switching frequency to push out more power to keep output voltage constant?

Thanks

Hely

AUX power supply

VS(R32) waveform at 13V output

0 Sheng-yang Yu1 over 3 years ago in reply to Hely Zhang

TI__Expert 4830 points

Zhang,

Due to PSR control law limitation, using UCC28911 in buck topology you can only achieve ~0.13A maximum output current.

I have a note in the following link showing the design flow I use when I design HV buck with UCC2891x or UCC2871x PSR controller.

https://txn.box.com/s/jfenkegexiaqislh3y9qu4zww30yyit2

If you want to have higher output current, you will need to use UCC287xx PSR controllers which allows higher peak current with external current sense resistor.

Regards,

Sheng-Yang Yu

0 Hely Zhang over 3 years ago in reply to Sheng-yang Yu1

TI__Intellectual 1160 points

Hi, Sheng-Yang

130mA is really low. but UCC287xx need external MOSFET, we don't want such external MOSFET solution for a high voltage buck supply.

Thanks

Hely

Power management

Power management forum

UCC28911: issue of PMP10676