UCC2897A: Condition when CS pin triggers overcurrent event

Ryotaro Fukui

Part Number: UCC2897A

Hello team,

I received some questions about overcurrent event of UCC2897A.

For their feasibility study, they are trying to calculate the conditions when overcurrent event occurs, including variation.

Therefore, they want to know the following values and their variations:

(1) What is the CT voltage? (Typical & variation) (Needs for calculating ISLOPE)

(2) What is the CS pin current? (Typical & variation) (Also described as 5 x ISLOPE in DS)

(3-1) What is the Overcurrent detecting threshold of CS pin signal? (Typical & variation) (0.5V?)

(3-2) Minimum CS pin pulse width that would trigger the overcurrent event (Typical & temperature variation)

Detailed information is provided in the attached Excel file. Please check it and contact us if there are misunderstanding about device function or other information needed.

Best Regards,

Ryotaro Fukui

UCC2897A_inquiry_20210727.xlsx

over 4 years ago

0 Eric Reicher over 4 years ago

TI__Expert 7900 points

Hello Ryotaro,

I understand their questions on the UCC2897A. I don't have all the answers at this moment, but I will speak with '2897A expert early next week and provide responses on Tuesday, August 3rd.

Best regards,

Eric

0 Eric Reicher over 4 years ago

TI__Expert 7900 points

Hello again Ryotaro,

I spoke with a Senior Applications engineer and a Design engineer.

1) The CT voltage is typically 2V.

2) The CS pin current is typically 5.0 x Islope, as you know. A Design engineer told me current mirror matching for a CMOS process is usually within +/- 5% for a relatively low gain, like 5.0.

3-1) The CS Over Current threshold is on page 7 of the data sheet: Vcs = 0.43Vmin, 0.48Vtyp, 0.53Vmax.

3-2) I was told the propagation delay from CS threshold (Vcs) to OUT is typically 75ns.

Note: When choosing RF and CF, set the -3dB frequency to fsw/10 to remove small transients from the current sense waveform.

In case the customer has not seen them, here are links to Application Notes for designing with the UCC2897A. The first App. Note covers Slope Compensation, but equations 15 to 19 should be of use to them for calculating the over current threshold (Vcs).

https://www.ti.com/lit/an/slua837/slua837.pdf?ts=1627915396766&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FUCC2897A%253FkeyMatch%253DUCC2897A

https://www.ti.com/lit/an/slua535a/slua535a.pdf?ts=1627915771909&ref_url=https%253A%252F%252Fwww.ti.com%252Fproduct%252FUCC2897A%253FkeyMatch%253DUCC2897A

Regards,

Eric

0 Ryotaro Fukui over 4 years ago in reply to Eric Reicher

TI__Intellectual 2345 points

Hello Eric,

Thank you for your feedbacks. I appreciate your prompt response. There are a few points that I would like to farther confirm about your answer.

1) Is there any information on how much the CT voltage variation will be?

3) In the high temperature environment, the customer measured that the over-current protection state has been entered earlier than normal temperature. (Which means CS voltage pulse width got narrower)

Did the propagation delay become shorter than typical value due to the temperature increase? The purpose of this question is to verify that this high temperature behavior is normal.

Regards,

Ryotaro Fukui

0 Eric Reicher over 4 years ago in reply to Ryotaro Fukui

TI__Expert 7900 points

Test group has a question on #1: What is the exact part number/package?

2) Also, how much did the over-current protection change (before and after values) and what was the temperature increase?

Power management

Power management forum

UCC2897A: Condition when CS pin triggers overcurrent event