TPS54JB20: Junction Temperature Calculation

Evan Wang

Genius 9330 points

Part Number: TPS54JB20

Hi All,

We have a question about how to calculate the junction temperature of TPS54JB20.

As we know the IC have multiple thermal metric parameter in the D/S.

If we want to calculate the TJ based on the power loss we got from WEBENCH simulation.

Which parameter would you recommend to use?

RθJA ? ΨJT?......

BRs,

Thank you.

over 4 years ago

0 David_Daniels over 4 years ago

TI__Mastermind 23580 points

The easiest is RthetaJA and to use equation 1 https://www.ti.com/lit/an/spra953c/spra953c.pdf#page=2

0 Evan Wang over 4 years ago in reply to David_Daniels

TI__Genius 9330 points

Hi David,

1. The reason I ask about the thermal metric is because we use the WEBENCH and find the power loss will be around 4.9W under below condition:

https://webench.ti.com/power-designer/switching-regulator/customize/3?VinMin=12&VinMax=12&O1V=5.052&O1I=7.2&base_pn=TPS54JB20&AppType=None&Flavor=None&op_TA=60&origin=pf_panel&lang_chosen=en-US&optfactor=3&Topology=Buck&flavor=None&VoltageOption=None

Vin: 12V

Vo: 5.052

Io: TDC 7.2A / Peak 15A

Lo: 0.75uH

Fs: 800kHz

Then if we use RthetaJA based on 60oC TA, the TJ will be too high.

49oC/W * 4.9W + 60oC = 300oC....

So I was wondering how to calculate the right TJ based on the thermal metric.

2. I would like to check with you that we saw two RthetaJA in the DS, which one should we use? 49 or 24.1?

+1 Dingmin Xu over 4 years ago in reply to Evan Wang

Intellectual 490 points

Hi,

The RthetaJA will be different between different board and layout, you can add a heatsink to reduce it or remove copper layer to increase it. The one in D/S is a reference value.

Thanks!

0 Evan Wang over 4 years ago in reply to Dingmin Xu

TI__Genius 9330 points

Hi Dingmin,

So would you recommend to verify the performance based on the real testing result?

I think it would be hard for customer to have a estimation in advance.

+1 Dingmin Xu over 4 years ago in reply to Evan Wang

Intellectual 490 points

Hi,

I think that will be a option, even after the estimation, the real testing is normally not omissible.

Please make sure the worst case has been considered and having enough margin. Luckily, many TI device contain thermal shutdown feature to prevent thermal damage.

Thanks!

0 David_Daniels over 4 years ago in reply to Evan Wang

TI__Mastermind 23580 points

The 4.9W seems high. Yesterday, I asked my team to look at the pdiss for the 800kHz compared to the 600kHz, 1000kHz setting. Try the 600kHz setting.

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TPS54JB20: Junction Temperature Calculation