UCC28064A: TSET resistor selection guide lines

balasubramani r

Part Number: UCC28064A
Other Parts Discussed in Thread: UCC256301

Hi ,

Im working on power supply design with UCC28064A IC with UCC256301. Iam Planning to use 40KHz as my minimum frequency considering inductor size. But using the formula available in datasheet i couldnt get the expected values. It is completely different.

My KBO=61.9

Ton Max-18uS

Vmin=85VAC

Using this formula i could get the expected value. Whether this formula is correct or not? Can anyone help me out with this query.

What shall be the Tset value?

over 5 years ago

0 Hong Huang over 5 years ago

TI__Guru 60485 points

It sounds you cannot get Tset from the formula in the datasheet, but then you listed two formulas and you said you could get the expected value.
--- Can you clarify which formulas in the dataseeht you cannot use it to get the expected values, and what are your expected values?

The you were asking " Whether this formula is correct or not?" do you mean the two formulas you listed?

If you want to get Tset quickly and not stuck here, can you use the excel spread sheet for you design? www.ti.com/.../sluc645

If you want to check and review the datasheet and your design calculation, please provide your calculation details, and point out where you think something not correct or out of your expectation so we can help to review?

0 balasubramani r over 5 years ago in reply to Hong Huang

Expert 1170 points

Hi Hong,

As per excel sheet the expected value is 75 to 80Kohms. But with the datasheet formula it is coming more than 100Mohms . Im sure my calculator doing right.

For design calculation i have given required data in the previous post.

For

Kth_min= 0.36

Ktl_min=3

Please advise what im missing

0 Hong Huang over 5 years ago in reply to balasubramani r

TI__Guru 60485 points

Please provide your calculation detail how your obtained 100Mohms. Your message has to be show all your calculation detail so we can check where we can find something different.

0 Hong Huang over 5 years ago in reply to Hong Huang

TI__Guru 60485 points

How did you obtain 100M? Where did you make different if comparing yours to the below?

I need to show your detail like the below so we can help to find where something is different.

0 balasubramani r over 5 years ago in reply to Hong Huang

Expert 1170 points

Hi Hong,

The values in the formula is correct but ,

Kindly note it.Ton_max is 18uS. ie 18x10^-6

Then this 10^-6in the denominator will go to numerator i guess and this 85.1k will become 85.1x10³x10⁶

This whole value becomes more than 85Mohms .

Correct me if im wrong .

0 Hong Huang over 5 years ago in reply to balasubramani r

TI__Guru 60485 points

Based on the datasheet, KTH_MIN = 0.36 us/V. So us in 18us is cancelled out by us in 0.36us/V.

0 balasubramani r over 5 years ago in reply to Hong Huang

Expert 1170 points

Hi Hong,

Thanks for your interest .. Now I got clear view where i missed things.

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UCC28064A: TSET resistor selection guide lines