UCC28950 spreadsheet possible issue

Jeferson Staudt1

Prodigy 30 points

Other Parts Discussed in Thread: UCC28950

Hello there.

I'm designing a DC/DC converter using the UCC28950. The specifications os the power supply are:

Vin = 390Vdc (PFC)
Vout = 48V
Iout = 21A

I was using the the spreadsheet avaliable in the following link:
http://www.ti.com/litv/zip/sluc222b

But, I believe it has a little issue. In the tab called "Design Information" rolling the sheet down, after the graphic, the resistor called RDELEF must be defined more the once. It must bemn defined in the follwowing places:
"Setting AF and BE..."
"Setting Minimum on Time"
"Setup PWM..."
"Setup Slope Compensation"

If thats not an error which value I must consider?

over 12 years ago

0 Flavio Caduda over 12 years ago

Prodigy 120 points

Indeed, the R_DELEF variable is calculated multiple times on the spreadsheet.

Which one is to be considered when designing the converter? Or are we missing something?

0 Ed Walker over 12 years ago in reply to Flavio Caduda

Prodigy 5 points

The multiple uses of Rdelef is a copy/paste error in the spreadsheet.
Rdelef only applies to the Adelef delay setting for the EF outputs.
I can see that the EF delay is the first instance, then those cells were used for the following blocks without the R designator being changed.

Rtmin is used for setting minimum ON time.
RT is used to set the switching frequency.
Rsum is used for slope compensation.
In these 3 cases ignore the use of Rdelef and replace it with the resistor used for that function.

I will let the spreadsheet author know of the error.

0 Ed Walker over 12 years ago in reply to Ed Walker

Prodigy 5 points

The updated excel file SLUC222C.xls (rev C) should be up on the TI web very soon.

0 Mike O' over 12 years ago in reply to Ed Walker

TI__Guru* 85926 points

Here is the updated file if you are interested thanks for pointing out there were issues with it.

UCC28950 Excel Design Tool_SLUC222C.xls

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UCC28950 spreadsheet possible issue