UCC28220: SLOPE compensation and equation 9

Noriyuki Takahashi

Part Number: UCC28220

Tool/software:

Hi team,

Q1. It seems that the slope compensation is 25 according to the P.4, but it seems the value is 16.6 accroding to Figure 20 as below. How should they understand this difference?

Q2. This is similar question with below link.

https://e2e.ti.com/support/power-management-group/power-management/f/power-management-forum/540719/ucc28220-uvlo-ovlo-hysteresis-design-questions

As the figure below, the 1.26V and R4 doesn't have any affect on the circuit. And it is not clear to get equation (9). Could you clarify this confusion?

Regards,

Noriyuki Takahashi

7 months ago

0 Hong Huang 7 months ago

TI__Guru 73265 points

Hi,

Q1:

Please refer to the below for why. The Fig 20 shows a MathCAD directly copy while the below shows how 16.6 is obtained so it means that the number "25" is correct.

200-W Interleaved Forward Converter Design Review Using TI's UCC28221 PWM Contro

The circuit you provided is not equivalent to the device intends to do. IHYS is produced to produce a voltage specified by 1.26V x (R1/R4). It is not a parallel circuit like you show.

The diagram is to help to understand the HYS current instead of real and physical circuit inside.

0 Noriyuki Takahashi 6 months ago in reply to Hong Huang

TI__Genius 10950 points

Hi Hong,

Hong Huang said:
Please refer to the below for why. The Fig 20 shows a MathCAD directly copy while the below shows how 16.6 is obtained so it means that the number "25" is correct.

They understood that 25 is correct, not 16.6, but they don't know why youm mentioned about MathCAD here, and why it gets 16.6 when you copy it from the MathCAD. Could you explain this agian to avoid misunderstanding?

Regarding Q2, could you draw the circuit so that they can understand how to get the IHYS = 1.26V x (R1/R4)?

It is confusing, becasue it is not sure what information are correct or not.

Regards,

Noriyuki Takahashi

+1 Hong Huang 6 months ago in reply to Noriyuki Takahashi

TI__Guru 73265 points

Hi,

Q1,

Please refer to the below article. MathCAD word is on that figure caption so that figure is from a design example described by the below article section 2.10.

https://www.ti.com/lit/an/slua312/slua312.pdf?ts=1738600482493&ref_url=https%253A%252F%252Fwww.ti.com%252Ftool%252FUCC28221-CALC&_ticdt=MTczODkzMjE1MnxsaXRhZGMzMTc2Nzk3ODJmMWQ3YWQxYjFmfEdBMS4xLjE3Mzc5ODI3MTUuMTczNzk4MjcwNXxudWxsfG51bGx8R1MxLjEuMTczODkzMDg5MC4yNi4xLjE3Mzg5MzIxNTIuMC4wLjB8bnVsbHxudWxsfG51bGw

Q2,

No, the datasheet does not disclose this but just tells you a hysteretic voltage is introduced as 1.26x R1/R4 so just follow the equations for your design.

How it is achieved inside is not published then the associated detail is TI confidential.

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UCC28220: SLOPE compensation and equation 9