UCC14341-Q1: Circuit design resistor selection calculating problem

Hi,

* How do I get the correct value of  RLIM_MAX_H, RLIM_MAX_L1 and  RLIM_MAX_L2?:

[Hong] Equation 11 and Equation 12.

* RDR circuit component selection:

[Hong] Basically RLIM, but you can also refer to Fig 9-3

* RLIM1 which equation to use:

[Hong] It should use equation in UCC14341 datasheet. I will ask the excel sheet designer to clarify.

* What does the ΔCOUT mean in these equations?

My guess is that it is the tolerance of the capacitor, but I can't get the same value as the calculator.

[Hong] Yes, the capacitor value tolerance. I can be different based on your capacitor selection. I will also ask to clarify through the excel designer

Hi,

* How do I get the correct value of  RLIM_MAX_H, RLIM_MAX_L1 and  RLIM_MAX_L2?:

[Hong] Equation 11 and Equation 12.

* RDR circuit component selection:

[Hong] Basically RLIM, but you can also refer to Fig 9-3

* RLIM1 which equation to use:

[Hong] It should use equation in UCC14341 datasheet. I will ask the excel sheet designer to clarify.

* What does the ΔCOUT mean in these equations?

My guess is that it is the tolerance of the capacitor, but I can't get the same value as the calculator.

[Hong] Yes, the capacitor value tolerance. I can be different based on your capacitor selection. I will also ask to clarify through the excel designer

[Hong] Can you provide your excel sheet to show which capacitor values different?

Here is my excel sheet.

I did manage to get RLIM_MAX_L1 and RLIM_MAX_L2 to be the same value as UCC1434x-Q1_Calculator_V8.xlsx.

But I can't get RLIM_MAX_H right.

And in the calculator there are 4 capacitor tolerance, max.Cout2, min.Cout2, max.Cout3, min.Cout3,

but in the RLIM_MAX_H and RLIM_MAX_L1 equation, Equation 10 and Equation 11, there's just ΔCOUT2 and ΔCOUT3, so I'm not sure which capacitor tolerance these are.

I want to know which capacitor tolerance each ΔCOUT is.

And in the RLIM1 equation, Equation 14, it says ΔCOUT3_POS, so I guess it is max.Cout3.

And since the RLIM1 value in the Calculator is not using the Equation 14 in the datasheet, I can't confirm if my calculation is right or wrong.

UCC14341-calculate.xlsx

Hi,

I will need to talk to the excel design sheet creator. To help this, can you point me to which rows (with row #) you have problems with the calculations.

For example, (assume row 89, Cout1 not right) 

I've marked the places I have problems with the calculations in red.

row 25, RLIM_MAX_H not right

row 38, RLIM1 not right

row 39, RLIM2 not right

UCC14341-calculate_1.xlsx

Hi,

I will reply to you after I talk to the excel sheet designer.

Hi,

It looks the excel file you provided is from your own creation instead of the one downloaded from ti.com. Can you provide the excel sheet from ti.com but with your design requirements filled in and then point out where the differences between your own excel sheet and the sheet from ti.com in terms of row #?

This way can help to locate where the differences existing between two different excel sheets to help resolve differences more to the point.

Here is my own excel sheet creation and the excel sheet I downloaded from ti.com with my design requirements filled in.

The numbers in my design requirements is just random numbers to check if my own excel calculation is correct, so these can be changed.

the differences existing between my excel vs excel sheet from ti.com is:

row 30 vs row 55,56,57, Max. RLIM is different when Max. RLIM = RLIM_MAX_H from the datasheet.

row 38 vs row 62, Max. RLIM1 is different.

row 39 vs row 65, Max. RLIM2 is different.

And I also notice that the power losses of resistors are wrong, so

row 32 vs row 59, power loss rating of RLIM is different.

row 45 vs row 63, power loss rating of RLIM1 is different.

row 46 vs row 65, power loss rating of RLIM2 is different.

Basically everything related to ΔCOUT from the datasheet are wrong. 

UCC14341-calculate_2.xlsx

UCC1434x-Q1_Calculator_V8.xlsx

Hi,

I will review to find where differences are from.

Hi,

Can you check your RLIM_MAX_L1, it looks not in line with the below equation.

Also RLIM_MAX_H looks not match:

Why not using the TI excel design sheet to make your design? 

About RLIM_MAX_L1, I changed the equation to make the result match the value from the TI excel design sheet,

I used the following equation, and I did get the same value as in the TI excel design sheet

(using design numbers I filled, the RLIM(MAX) in the TI excel design sheet is RLIM_MAX_L1)

but I have no idea how this equation worked.

And about RLIM_MAX_H, I just can't get the value right.

If I use the equations directly from the datasheet equations (assuming all ΔCOUT are Max. component tolerance), the values calculated seem to be ridiculous, and can't match the value from the TI excel design sheet.(in the following excel file, I fixed the RLIM_MAX_L1 and RLIM_MAX_H equation to match the datasheet)

UCC14341-calculate_3.xlsx

So there must be some problem in the datasheet equations or TI excel design sheet or even both.

Hong Huang said:

Why not using the TI excel design sheet to make your design?

Because it is locked, therefore I can't see the equation used or change the design sheet or extend it,

and it seems to be still bugged,

like I mentioned in the original question, RLIM1 calculation in the TI excel design sheet is not using the equation from the UCC14341-Q1 datasheet.

And it even states "Place close to UCC1414x-Q1." in E70 while this is the design sheet for UCC1434x-Q1.

Hi,

There are reasons why the equations only use min values. I will ask the datasheet to find out. I do no think you can arbitrary to use max values to substitute the min values.

So if you follow the equations as they show, do you get the same results, right?

I will also find why E70 says that.

When you say ridiculous results, do you mea only from your excel sheet or from TI sheet as well?

I don't get the same result as the TI excel design sheet if I follow the datasheet equations,

this is why I need to try change the equation in the first place.

The equation above is the only way I can get the same result as the TI excel design sheet, and I think it is what the TI excel design sheet used.

I find out that, in the TI excel design sheet,

RLIM_MAX_L1 is only related to Max. component tolerance of COUT2 (C26) and Min. component tolerance of COUT3 (C29),

RLIM_MAX_H is only related to Min. component tolerance of COUT2 (C27) and Max. component tolerance of COUT3 (C28),

by filling C26~C29 with random numbers, 

so I used this to calculate, since the datasheet does not mention which(max or min) tolerance ΔCOUT are.

Hong Huang said:

When you say ridiculous results, do you mea only from your excel sheet or from TI sheet as well?

Only from my excel sheet.

Hi,

So can you please update your own excel sheet to use the same equations from the datasheet so you can get the same results as TI excel, then send your updated excel sheet to me for a look?

I am not understanding why sometimes you get the same results sometimes not. So please follow the datasheet equations accurately although you do not understand why the equations are presented like these in the datasheet which I can help to find next. On you side, you need to follow the datasheet equations accurately to update your own excel sheet then send to me.

Why do you need to use unlocked TI excel sheet? Why not just use the TI excel sheet results to make your design?

The problem is that the equations from the datasheet is unclear (2 ΔCOUT in the datasheet equation, but 4 capacitor tolerances in the TI excel sheet) so can't exactly follow the datasheet equations.

Hong Huang said:

use the same equations from the datasheet so you can get the same results as TI excel

Another problem is that the results from the datasheet equations do not match the TI excel,

I cannot use the same equations from the datasheet to get the same results as TI excel.

Hong Huang said:

Why not just use the TI excel sheet results to make your design?

Because the TI excel sheet is not following the datasheet equations, the results are different,

and especially, like I mentioned in TI excel, RLIM1 calculation (C61) is not using the equation from the UCC14341 datasheet.

so I don't know which result to use for my design.

Here is my updated excel using the datasheet equations, (assuming all ΔCOUT are Min. component tolerance because:

Hong Huang said:

equations only use min values

),

UCC14341-calculate_4.xlsx

the results are still not right.

Hi,

Please indicate which rows (by their row #) you do not know how to fill in.

I compared the equations between the TI excel sheet and the UCC14341 datasheet on your interested equations, they are identical. Please list which rows you think they do not use the same equations from UCC14341 datasheet.

I would focus on TI excel sheet and help to clarify the rows where you think something not good. I will not review your excel sheet unless really necessary as we believe TI excel sheet is correct - but if you see something in concern or not clear how to fill in, then we can help to work out.

I calculated RLIM_MAX_L1 and RLIM1 using equation (11) and equation (14) from the datasheet and the values I filled in the TI excel.

RLIM_MAX_L1 calculation:

RLIM_MAX_L1 = 4265.5 , but in TI excel it is 2236.2 (in row 55)

RLIM1 calculation:

RLIM1 = 13156.5 , but in TI excel it is 9321.3 (in row 61)

So I think at least for these two equations they are not identical.

I think, for RLIM_MAX_L1 calculation, the equation (14) in the datasheet is wrong.

for RLIM1 calculation, the equation used in TI excel is wrong.

Hong Huang said:

Please list which rows you think they do not use the same equations from UCC14341 datasheet.

Row 55, 59, 61, 63, 64, 66

Hi,

I will have a look and reply to you. This may need a few days to go through these details and also may need to talk to the sheet creator..

Hi,

Row 55 is for the RLIM1 without DLIM and RLIM2

Row 61 is for the RLIM1 with DLIM and RLIM2

So the results are not directly from the equations without considering the RDR options.

I have confirmed with the TI excel sheet designers, please use the TI excel sheet for your design. If you feel some rows not clear to you, please ask then we will help you to move on.  

So for RLIM_MAX_L1,  I should use 2236.2 (C55) in the TI excel sheet to choose the resistor, not the calculated 4265.5 using datasheet equation?

And if I'm using RDR option, for RLIM1, I should use 9321.3 (C61) in the TI excel sheet to choose the resistor, not the calculated 13156.5 using datasheet equation?

So you mean, for the circuit design, TI excel is right, the equations in the datasheet is wrong or not complete, don't use the equations in the datasheet.

I should just use the TI excel, am I right?

Hi,

The datasheet equations are correct when you use them in correct ways.

We suggest you use the TI excel design sheet which considers when these equations are used correctly,

You would need to read through the datasheet to use these equations in the same ways the excel sheet does.

But if you feel something unreasonable on the excel sheet or you think you do not agree or why you can ask.

For design purpose we suggest to use the TI excel sheet to move on.

So for Cin I choose 20 // 0.1 µF from the TI excel

not 10 + 0.1 µF from the datasheet?

I think there is no calculation involved here, but the value is still different so,

should just pick the TI excel one?