UCC28722 WBENCH reference design disparity

HPB

Other Parts Discussed in Thread: UCC28722, UCC28720, UCC28700, UCC28700EVM-068, PMP8519

I'm trying to design a flyback AC-DC supply with an output of 3.3V upto 1A. I noticed some weird behavior. If I try to get a WEBENCH design from the UCC28722 product page on the TI website it says that minimum Vout is 5V. However, if I run WEBENCH from its own page I can design a 3.3V supply. Is the UCC28722 suitable for a 3.3V supply? If yes, would the attached reference design work? I'm simply asking since I'll need to get a custom transformer made for this (even for prototyping purposes) and if this controller is not suitable it would be wasted expense for me.

UCC28722_webench_design_3851011_38_603457300.pdf

over 7 years ago

0 Brian Johnson96 over 7 years ago

TI__Expert 3200 points

I will get an AE involved to help answer your questions.

0 Mike O' over 7 years ago in reply to Brian Johnson96

TI__Guru 66005 points

Hello,

The device was designed for USB applications which are design for a 5V output. This is because of the constant current, constant voltage operation that generates the VI curve presented in figure 17 of the data sheet. So when you operating at Iocc the output voltage can drop from 5V down to 2V before shutting off.

The UCC28722 PSR controller can achieve an output accuracy of +/-5% steady state but can exceed this during a large transient (>20%). However, since these controllers were design for battery applications with lots of capacitance this is generally not an issue. If I recall correctly 3.3V applications are more critical when it comes to load transients. The UCC28722 may not be the correct device for this application. However, you should be able to design to regulate a 3.3V output if you desire, it should be an adjustment of the transformer turns ratio.

Regards,

0 John Stevens over 7 years ago

TI__Expert 7395 points

HPB,
UCC28722 or UCC28720 can support 3.3V but it is not typical application so we chose not to support that yet in Webench. I would suggest using the mathcad or excel design tool on the UCC28722 product page to help design your supply and not the webench. This can be found here: www.ti.com/.../toolssoftware

Alternatively, you could leverage this reference design using UCC28700 providing 3.3V at 1.5A max: www.ti.com/.../PMP8519

Let know if that reference design is preferred and you can email me to try to get you a board to use or Gerber/PCB files.

Regards,
John

0 HPB over 7 years ago in reply to Mike O'

Expert 1350 points

Thank you. This helps.

0 HPB over 7 years ago in reply to John Stevens

Expert 1350 points

Thank you. This helps too. Could please you let me know the email through which I can get the Gerbers/PCB files?

0 John Stevens over 7 years ago in reply to HPB

TI__Expert 7395 points

Hrishikesh,
Mike will provide them to your gmail email address on file with your myTI account.
Regards,
John

0 Mike O' over 7 years ago in reply to John Stevens

TI__Guru 66005 points

PWR068A_gbrs.zip

0 Mike O' over 7 years ago in reply to Mike O'

TI__Guru 66005 points

I contacted the power design services team and reference design PMP8519 was a modified UCC28700EVM-068. I attached the Gerber files earlier for your reference.

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UCC28722 WBENCH reference design disparity