TPS566238: Webench

Hi Haseen,

Thank you very much for your reply.

Those are Vin=12V(Min, Max), Vout=3.3V, Iout=6A as I wrote at the first post.

But they just want to get the answers to Q1/Q2 at this moment.

Could you please give me the answers?

Thank you again and best regards,
Kazuya.

Hi Haseen,

Could you please give me the answers to Q1/Q2?

Your reply would be much appreciated.

Thank you very much and best regards,
Kazuya.

Hi Haseen,

Thank you very much for your support.

I run webench with Peak current mode and Current limit mode.
I attached these result.

As the result, IC Ipk of peak current mode is higher than IC Ipk of current limit mode.

Could you please tell me why? 

Thank you again and best regards,
Kazuya.

WBDesign(tps566238_Vin=10p8_13p2V_Vo3p3V_Io6A_currentlimit).pdfWBDesign(tps566238_Vin=10p8_13p2V_Vo3p3V_Io6A_peakcurrent).pdf

Hi Haseen,

Thank you very much for your support.

I know you are very busy.
But the customer want to get your answer as soon as possible.

Could you please give me your answer?

Thank you again and best regards,
Kazuya.

Hi Haseen,

Thank you very much for your supports.

Their conditions are Vin=12V+/-10%, Vo=3.3V, Io=6A.
Could you check what the inductor value is?

!s it better to not use the webench tool for TPS56638 at this moment?

Thank you again and best regards,
Kazuya.

Hi Haseen,

Thank you very much for your calculation.

Do you use any calculation tool for this inductor calculation.
If yes, could you please give me the tool?

If no, could you please calculate inductor value for the following conditions because they are concidering using TPS56638 for these.

1. 12V->3.3V/5.2A

2. 12V->5V/4.8A

3. 12V->1.1V/2.6A

4. 12V->1.8V/2.1A

5. 12V->5V 1A

Also how is the checking of TPS56638 webench operation?
Did you find any problem of the webench?

Thank you again and best regards,
Kazuya.

Hi Haseen,

Thank you very much for the tool sending.

But the customer wanted to get a calculation tool for inductor value calculation.
The cell of  "L" (Inductor) in the excel you sent me is input mode.

Do you have any calculation tool which can calculate inductor value for TPS56638?

If you don't have the tool, could you please give me the inductor value for the following conditions?

1. 12V->3.3V/5.2A

2. 12V->5V/4.8A

3. 12V->1.1V/2.6A

4. 12V->1.8V/2.1A

5. 12V->5V 1A

Also did you find any problem of TPS56638 webench?

Thank you again and best regards,
Kazuya.

Hi Haseen,

They have a question about the following your explain for inductor current in current limiting case.
"At full load peak inductor current is 6+(0.5*1.8)=6.9A where as peak inductor current during current limit is 7.8+(0.5*2.34)=8.97A"

They think the response speed of the current limit circuit is fast, so if the current limit value is 7.8A, I don't think the inductor current will exceed 7.8A.
So I think that the peak current of the inductor will be 7.8A, and Io = 7.8A-(2.34V/2) = 7.8-1.17 = 6.63A.

Is their thought not correct?

Thank you very much and best regards,
Kazuya.

Hi Haseen,

Could you please give me your reply because the customer wants to get your reply ASAP?

Thank you very much and best regards,
Kazuya. 

Hi Haseen,

Thank you very much for your reply.

The customer wants to know the followings same as the first question of this thread.
Q1.　What is difference between "Peak Current" and "Current Limit" of "Minimum Inductor Current Rating" in TPS56638 webench?

You explained us as the follow.
In general inductor current limit is more than inductor peak current.
For example the load current is 6A and assume 130% is current limit in the output i.e 7.8A.
Inductor peak-peak ripple current = 0.3*Load
At full load inductor peak-peak ripple current is 0.3*6 =1.8A and for Current limit =0.3*7.8=2.34A.
At full load peak inductor current is 6+(0.5*1.8)=6.9A where as peak inductor current during current limit is 7.8+(0.5*2.34)=8.97A

After that I run webench with Peak current mode and Current limit mode.
I attached these result.

As the result, IC Ipk of peak current mode is higher than IC Ipk of current limit mode.

2664.WBDesign(tps566238_Vin=10p8_13p2V_Vo3p3V_Io6A_peakcurrent).pdf

0116.WBDesign(tps566238_Vin=10p8_13p2V_Vo3p3V_Io6A_currentlimit).pdf

Your reply after these question was that there is some discrepancy in our webench tool for this TPS56638 part and we are looking into this webench calculations.

Was there any problem in TPS56638 webench?  Or was any problem not find? 

Thank you again and best regards,
Kazuya.

Hi Haseen,

Thank you very much for your strong supports.

I understand that you are working with the Webench team to make corrections.
Could you please tell me the inductor value for the following customer conditions?

1. 12V->3.3V/5.2A
2. 12V->5V/4.8A
3. 12V->1.1V/2.6A
4. 12V->1.8V/2.1A
5. 12V->5V 1A

Or is there any tool that can calculate the inductor?
Do you have a revised version of the Excel file you sent me previously? I couldn't figure out how to use the previous version.

The customer want to know the following.

Q1.　What is difference between "Peak Current" and "Current Limit" of "Minimum Inductor Current Rating"?

You explained us as the follow.
In general inductor current limit is more than inductor peak current.
For example the load current is 6A and assume 130% is current limit in the output i.e 7.8A.
Inductor peak-peak ripple current = 0.3*Load
At full load inductor peak-peak ripple current is 0.3*6 =1.8A and for Current limit =0.3*7.8=2.34A.
At full load peak inductor current is 6+(0.5*1.8)=6.9A where as peak inductor current during current limit is 7.8+(0.5*2.34)=8.97A

Is this explanation correct?
If yes, I will explain this to the customer.

Thank you again and best regards,
Kazuya.

Haseen,

Thank you very much for your strong supports.

The customer wants to know the difference ASAP.
Could you give me your reply?

Thank you again and best regards,
Kazuya.

Hi Kazuya,

Yes the above explanation is correct with respect to Peak current and Current limit.

I will share you the excel with inductance calculation for below

1. 12V->3.3V/5.2A
2. 12V->5V/4.8A
3. 12V->1.1V/2.6A
4. 12V->1.8V/2.1A
5. 12V->5V 1A

Regards,

Haseen.

Hi Haseen,

Thank you very much for your strong supports.

I will inform this calculation result to the customer.

At this moment, they have an additional question as the below.
Could you please give me your reply?

Q.
At section 7.2.2.3 in TPS56638 datasheet, we can see the following description.

>During transient and short-circuit conditions, the inductor current can increase
>up to the current limit of the device. This means that choosing an inductor
>with a saturation current higher than the peak current under current limit condition is safe.

I think TPS56638 has valley current limit.
In case of TPS56638, how should I understand this description meaning?

Thank you again and best regards,
Kazuya.

Hi Haseen,

Thank you very much for your telling me the good application note.

Could I ask you the following question about Figure 2. Valley Current Limit Example Using Constant On-time Control
in the application note because I got question the customer?

Q.
TPS56638 has valley current limit. the maximum value of the current limit, IOLC(Max) is 8.9A.
They think that according to Figure 2, the peak current of inductor is inductor ripple current, Ip-p + 8.9A when IOLC is 8.9A.

For example, when Ip-p=2.7A(9A*0.3=2.7A), they think that the peak current of inductor would be 11.6A(8.9A+2.7A).

Is their thought correct?

Your reply would be much appreciated.

Thank you again and best regards,
Kazuya.

Hi Haseen,

Could you give me your reply?

Thank you and best regards,
Kazuya.