TPS40200: Calculate Psw and Pcross

Yuto Sakai

Part Number: TPS40200

I calculated equation 10 and 12,but the calculated result is not match.
Could you let me know the value of the parameter you used on equation 10 and 12?

Best Regards,

Yuto Sakai

over 8 years ago

0 JohnTucker over 8 years ago

TI__Guru**** 191445 points

For EQ 10, You need to first calculate EQ 11. What did you use for RG, and VTH?
For EQ 12, it looks like they used Vin nom = 12 V instead of Vin max. With Vin = 12 V, Pcross = 2 mW approximately.

0 JohnTucker over 8 years ago in reply to JohnTucker

TI__Guru**** 191445 points

I looked into EQ 10 also. It is impossible to verify as I do not know what values the original author used for some of the variables. I will flag this issue in Support Analyzer and close this thread.

0 Yuto Sakai over 8 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

As in Fifure 31 ,I use FDC654P.

But, I don't know which value of RG and VTH to refer to datasheet of FDC654P.

Could you tell me about these values?

Best Regards,

Yuto Sakai

0 JohnTucker over 8 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

They are not in the datasheet. I did not write it, so i do not know what values the original authors used. Researching this, Vth might be 1.6 V or 1.9 V. Rg might be 4.7 ohm. This may or may not be what the author used in the datasheet equation.

0 Yuto Sakai over 8 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

Thank you for your reply.

I continue to calculate EQ10 and EQ12 of the datasheet , but my calculation does not match.

Q1,

I used Vth=1.9V and Rg=4.7ohm when I calculate EQ10,but the calculation did not match.

According to the datasheet of FDC654P,RGEN is 6ohm on page 3.

(FDC654P's datasheet URL:https://www.fairchildsemi.co.jp/datasheets/FD/FDC654P.pdf)

That's why I think that Rg is RGEN.

And I think that Vth is 8V(DRV pin typical output).

As a result of calculation(Rg=6ohm,Vth=8V), Psw became 9.5mW.

Is this correct?

Q2,

Could you confirm with the person in charge if you do not know this answer?

Best Regards,

Yuto Sakai

0 JohnTucker over 8 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

The gate threshold voltage should be 1.6 V or 1.9 V, depending on which datasheet you look at (I checked a couple equivalent parts as well). I see RG values of 4.7 or 6 ohm. It is impossible to know what the original author used. Also, I so not know what value was used for Ipk. The equations appear to correct, so I would not worry that your calculation does not match the datasheet result.

0 Yuto Sakai over 8 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

I would like to know the detail of the calculation since our custormer will not use TPS40200.
Could you tell me the person in charge?

Best Regards,
Yuto Sakai

0 JohnTucker over 8 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

I have assigned this thread to the applications manager for that product family. As TPS40200 was assigned to them recently, they will not know the answer. The datasheet was written over 10 years ago, so it is unlikely anyone would remember. I'll load these equations into Mathcad, and see if I can juggle the input to match the results.

0 Yuto Sakai over 8 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

Thank you for your kind support.
I'm looking forward to hearing from you.

Best Regards,
Yuto Sakai

0 JohnTucker over 8 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

I built an excel spreadsheet. I can make Eq 11 work by using 8 V for Vgate. I can make eq 12 work by using Vin nom = 12 V instead of Vin max = 16 V. I get something near 6.2 mV for Eq 10. I cannot see any way to get 10 mW, but I do notice the turn on and turn off times are exceptionally fast. If you use tr and tf instead of Tchon and Tchoff, you get a much more reasonable 8.55 mW.

0 Yuto Sakai over 8 years ago in reply to JohnTucker

Mastermind 6100 points

Hi John-san,

Thank you for your reply.

I’m wondering if it would be possible to give me the excel spreadsheet?

Best Regards,

Yuto Sakai

0 JohnTucker over 8 years ago in reply to Yuto Sakai

TI__Guru**** 191445 points

Sure, just give me your email.

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TPS40200: Calculate Psw and Pcross