WEBENCH® Tools/TPS40304: If TPS40304 external component will also change after we change key component?

Chen Bogey8

Mastermind 9990 points

Part Number: TPS40304
Other Parts Discussed in Thread: CSD16340Q3, CSD16323Q3, CSD17573Q5B

Tool/software: WEBENCH® Design Tools

Hi Sir

I use TPS40304 to run Vin 12V and Vout 1.2A/Iout 25A.

initial run out high side MOS(M1) is CSD16340Q3 and Rs is 3.32Kohm.

and i change high side MOS to CSD16323Q3, the Rs is still 3.32Kohm.

I use DataSheet 7.3.5, the calculate Rs should be around 8K. May we know which is correct?

as below are some parameter that i use. the Rs is for adj OCP. so i am want sure what is correct.

CSD16323Q3 = 4.4mOhm (Vgs=4.5V)

Ip-p = 25A * 0.3 = 7.5A

Bogey

over 6 years ago

0 Mahantesh Chanagoudar over 6 years ago

TI__Intellectual 1045 points

Hi Bogey,

We are looking into this. Will get back to you soon.

Best Regards,
Mahantesh

0 Mathew Jacob1 over 6 years ago

TI__Expert 5900 points

Bogey,

Your calculations are correct. By the way the calculations use the low side FET Rdson and not the high side.

Regards,

Mathew

0 Chen Bogey8 over 6 years ago in reply to Mathew Jacob1

Mastermind 9990 points

Hi Mathew
From datasheet 8.2.1.2.10 , it is show high side MOS FET, i have confuse~.
by the way if customer want to up to iout= 30A, can i use webench to run 25A first. and just modify OCP risistor. is it enough that inductor use 0.47uH/37A and low side MOS paraller more one CSD17573Q5B? is there other point i have no notice?
Bogey

0 Mathew Jacob1 over 6 years ago in reply to Chen Bogey8

TI__Expert 5900 points

Bogey,

From datasheet 8.2.1.2.10, these equations refer to Figure 14 where Q1 is the sync fet or bottom fet. However I can see its not consistent in datasheet and some other figures have Q1 as top fet.

Anyway the equation refers to Q1 and Fig 14.

Yes it would be better to use low side parallel fets to keep the heat dissipation spread however it also depends on max ambient temp of application etc.

Regards,

Mathew

0 Mahantesh Chanagoudar over 6 years ago in reply to Mathew Jacob1

TI__Intellectual 1045 points

Bogey,

With an existing Webench infrastructure, for a case like this when you chose alternate component in the schematic , WEBENCH won't do re-design and only the OpVals parameters will change. For that reason, "Rs" value is not getting updated.

Best Regards,
Mahantesh

0 Robbie Tomaszewski over 6 years ago in reply to Mahantesh Chanagoudar

Prodigy 80 points

When will this problem be fixed in WEBENCH? Being able to change a component like the bulk capacitor on the output of SMPS and then running an accurate transient simulation is important to the design of VDDQ power.

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WEBENCH® Tools/TPS40304: If TPS40304 external component will also change after we change key component?