TPS56C215: Why TPS56C215 thermal poor than TPS53515 when same condition

Jimmy Wang27

Prodigy 250 points

Part Number: TPS56C215
Other Parts Discussed in Thread: TPS53515

Hi team,

I used webench to run the thermal simulation and found some problem. I compare TPS56C215 and TPS53515 parameter.

whatever Rdson and thermal information TPS56C215 parameters were better than TPS53515.

So my question is why Tj poor than TPS53515?

Test condition

TPS56C215 TPS53515

Vin=12V

Vo=1.2V

Io=12A

FSW=400kHz

over 6 years ago

0 Edwin Zang over 6 years ago

TI__Expert 6425 points

Hi Jimmy,
Got it, I will try to find the reason and reply you later.
BRs,
Edwin.

0 Sam(MPAA) Zhang over 6 years ago

TI__Mastermind 19080 points

Hi Jimmy,

First of all, the parameters you got from datasheet are all right. I've verified the issue on Webench.

In Webench model, you may notice there is a parameter "Effective IC Junction-to-Ambient Thermal Resistance". This parameter can be used to evaluate the Tj on EVM operation. For this parameter, TPS56C215 is still better than TPS53515.

The problem here is, efficiency of TPS56C215 on Webench is lower than it should be, so the power dissipation is larger. You may refer to the Figure 13 on datasheet, the full loading efficiency is higher than Webench data - 82.88%.

Regards,

Hao

0 Jimmy Wang27 over 6 years ago in reply to Sam(MPAA) Zhang

Prodigy 250 points

Hi Sam,

Thank you for great support!

But I would like to know TPS56C215 could replace TPS53515 when same condition?

Because my customer has a cost issue when some project.

BTW, About thermal I think the package size TPS56C215 poor than TPS53515 and I can't find internal MOSFET another parameter.

(ex Qg, Parasitic parameter). So I think TPS56C215 switching loss may be larger.

0 Sam(MPAA) Zhang over 6 years ago in reply to Jimmy Wang27

TI__Mastermind 19080 points

Hi Jimmy,

According to the parameters, TPS56C215 should be better from thermal perspective.
Usually only Rdson is listed in the EC table. Other internal MOSFET parameters are not provided.
In the condition of high output current, conduction loss dominates the total power loss. Switching loss doesn't matters a lot. I've got a result in the test before, you may take it as reference.
12V to 1.1V, 400kHz, room temperature, case temp is 58C @10A, 68C@12A.

Regards,
Hao

0 Jimmy Wang27 over 6 years ago in reply to Sam(MPAA) Zhang

Prodigy 250 points

Hi Hao,

I understood conduction loss dominates the total power loss.
but why TPC56C215 PD higher than TPS53515 on Webench Model? (Note: Rdson almost same)

0 Sam(MPAA) Zhang over 6 years ago in reply to Jimmy Wang27

TI__Mastermind 19080 points

Hi Jimmy,

The PD comes from the efficiency data. You may notice that at your operating condition, the efficiency of TPS53515 and TPS56C215 at 12A is 86.8% and 82.9%, respectively. It doesn't make any sense. So I guess there might be something wrong with TPS56C215 Webench efficiency model.
I've some more credible bench test result for TPS56C215 efficiency. If you are interested, I can share the data to you. Please leave your email here. Thanks!

Regards,
Hao

0 Jimmy Wang27 over 6 years ago in reply to Sam(MPAA) Zhang

Prodigy 250 points

Hi Hao,

OK, Thanks
Email: Jimmy.wang@wtmec.com

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TPS56C215: Why TPS56C215 thermal poor than TPS53515 when same condition