UCC28780: Negative value of OPP Resistor Excel Design Calculator

Mo Mo

Prodigy 130 points

Part Number: UCC28780

Hello TI team,

I'm designing a power supply using the Excel Design Calculator. Vin = 115V;400Hz. Vout=32V; 35W.

I fixed an OPP of 180%.

Is it normal that i have a negative value of recommended OPP resistor (-24115Ohms) ?

Thank you in advance.

Best.

over 3 years ago

0 Jaden Ning over 3 years ago

TI__Expert 7080 points

Hi MoMo,

It's abnormal that you got a negative value of OPP resistor , can you attached your calculator file so we can help to review it ?

Thanks.

0 Mo Mo over 3 years ago in reply to Jaden Ning

Prodigy 130 points

Copie de calculs CCCB.XLSX

Hi Jaden,

Attached the calculator file.

Thanks.

0 Jaden Ning over 3 years ago in reply to Mo Mo

TI__Expert 7080 points

Hi MoMo,

I have reviewed your calculator, the actual current sense resistor you inputted is higher than recommended , that is results in a negative OPP resistor .

Thanks.

0 Mo Mo over 3 years ago in reply to Jaden Ning

Prodigy 130 points

Hello Jaden,

Thank you for your answer.

Nevertheless, for another calculator (7W - 30V output), I still have a negative OPP resistor eventhough my current sense resistor is very close to the recommended one.

Please find attached the calculator.

calculs SIB_maj_MF.XLSX

0 Jaden Ning over 3 years ago in reply to Mo Mo

TI__Expert 7080 points

Hi Mo Mo,

The latest calculator version on TI.com is SLUC664C , while you are using is SLUC664B version. Could you please try to use the latest version.

BTW, it's not recommend to chose ACF for a 7W design. it will not brings you too much benefits for a such low power level design. while you have to spent much cost and effort on debug it.

Thanks.

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UCC28780: Negative value of OPP Resistor Excel Design Calculator