WEBENCH® Tools/DRV8825: TI PCB thermal simulation Tools : results seems very strange

thierry venet

Intellectual 465 points

Part Number: DRV8825

Tool/software: WEBENCH® Design Tools

Hello everybody,

When I try the PCB thermal calculator Tools from TI, the results seems very strange.

For example if I try with the motor driver DRV8825, I get this result (for 2.86W)

When I read the application note from TI, "calculating motor drivers power dissipation (SLVA504), we have this example :

In the note, we have 115.4°C for 2.86W power on a standard JEDEC PCB (I assume 2s2p PCB).

On the simulation Tools, for 2.86W, we have 144°C even for the largest PCB

Is there someone that can explain me the result ?

Best regards,

Thierry

over 5 years ago

0 thierry venet over 5 years ago

Intellectual 465 points

The screenshot are not visible in the post.

From the tool :

From the note :

0 Umayal Ramanathan over 5 years ago in reply to thierry venet

TI__Expert 5780 points

Hi Thierry,

We are looking for the right contact to address the query.Our experts will soon get back to you.

Thanks and Regards,

Umayal

0 Harman over 5 years ago in reply to Umayal Ramanathan

TI__Expert 7845 points

Thierry,

Sorry about the delay in our response. We are looking into the model & code to try to pinpoint the reason for inconsistencies that you pointed. This is taking some time, so we will follow up again by end of this week.

0 thierry venet over 5 years ago in reply to Harman

Intellectual 465 points

Hello Harman,

OK no problem, thanks for the feedback.

thierry

0 Harman over 5 years ago in reply to thierry venet

TI__Expert 7845 points

Thierry,
After looking into this a bit more and consulting with our thermal experts, here is what we found:

The PCB used in the thermal calculator is not the same as the JEDEC standard PCB (that you referenced in app note SLVA504), so the junction temperature estimates from the two may not match in many cases. For inline packages such as PWP, the thermal simulation data required for the tool’s interpolation calculations is generated using the PCB layout mentioned in Figure 9 on Page 9 of App Note SLUA566A: http://www.ti.com/lit/an/slua566a/slua566a.pdf. It is a single layer PCB with larger spreading copper planes on the top layer. In contrast, the JEDEC standard PCB is a 4 layer PCB with thermal vias beneath the exposed pad connected to one of the internal planes. Because the PCB represents a large portion of the junction to ambient thermal resistance, differences between the two PCB layouts can result in different predictions of junction temperature.

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WEBENCH® Tools/DRV8825: TI PCB thermal simulation Tools : results seems very strange