TPS65911: Inductor and Rtrip of VDDctrl

Dice-K

Part Number: TPS65911
Other Parts Discussed in Thread: CSD87330Q3D, 66AK2G12

Hi support team,
This is a confirmation about VDDctrl parts selection.
I would like to confirm how to calculate the inductor and Rtrip.

What design requirements led to these recommendations?

What values did you use in the above formula?

VOUT = 1V
VIN = 5V?
fSW = 340kHz?
IOUTmax = 2.9A?
KIND = 0.3?
ITRIP = 10μA
RDS(on) = 17mΩ?

The low-side RDS(on) of the recommended FET CSD87330Q3D is about 5mΩ, so the calculations do not match.

Regards,

Dice-K

over 1 year ago

0 Daniel W over 1 year ago

TI__Genius 13216 points

Hi Dice-K,

Bandwidth has been limited today. Please expect a response tomorrow.

Thanks,

Daniel W

+1 Daniel W over 1 year ago in reply to Daniel W

TI__Genius 13216 points

Hi Dice-K,

The first equation is based on the design process outlined in this document

The second equation is explained by the following description of Rtrip from the datasheet.

The equation can be evaluated using the following values using the nominal component values from the datasheet and Rds(on) you have provided.

Rds(on): 5mΩ
Iout(max): 10A
Itrip: 10μA
Rtrip: 40kΩ

0 Dice-K 11 months ago in reply to Daniel W

Mastermind 6390 points

Hi Daniel,
Thank you for your reply.

If Iout(max) = 10A, the equation for calculating "L" does not match.

According to the document below, the required current for the CVDD pin of the 66AK2G12 is "2735.79mA".

https://www.ti.com/jp/lit/an/sprace1/sprace1.pdf

(Ii is about 2.9A if you give it a margin.)

Are the following ideas correct?
・Iout(max) for L selection calculation is 2.9A, which is close to reality.
・Iout(max) for Rtrip selection calculation is 10A with a large margin.

Best regards,
Dice-K

0 Phil Yi40 11 months ago in reply to Dice-K

TI__Mastermind 33820 points

Hi Dice-K,

Daniel is on vacation; I'm trying to provide answers today; but found I need more time to study and give you update tomorrow.

Thanks!

Phil

0 Dice-K 11 months ago in reply to Phil Yi40

Mastermind 6390 points

Hi Daniel and Phil,

I would like an answer as to whether the following thoughts are correct.
・2.9A is for inductor selection.
・10A is for current limit setting

Best regards,
Dice-K

0 Megan Singer 11 months ago in reply to Dice-K

TI__Expert 4380 points

Hi Dice-K,

I apologize for the delay. Both Phil and Daniel are out of office at the moment. Phil is returning to the office on Tuesday, May 30. Please expect a delay in their responses.

Regards,
Megan

+1 Phil Yi40 11 months ago in reply to Megan Singer

TI__Mastermind 33820 points

Hi Dice-K,

I'm still on my vacation but just got chance to check the e2e and found this is kind of urgent which has lasted more than 1 week. I'm trying to provide my feedback here: If 2.9A is selected as max inductor current; 10A is too much for the current limit setting; 4A to 5A should be enough.

Thanks!

Phil

0 Dice-K 11 months ago in reply to Phil Yi40

Mastermind 6390 points

Hi Phil,
Thank you for your reply.

After all, is it correct to make "IOUTmax" in equation (3) larger than the actual output current?

Dice-K

+1 Phil Yi40 11 months ago in reply to Dice-K

TI__Mastermind 33820 points

Hi Dice-K,

Yes; but no need to make it too much; 2x should be good enough.

Thanks!

Phil

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TPS65911: Inductor and Rtrip of VDDctrl