TLV755P: difference of thermal resistance between theta(j-a) and theta(j-c)

Shinichi Inoue

Guru 21701 points

Part Number: TLV755P

Dear Specialists,

My customer is considering TLV755P and has a question.

I would be grateful if you could advise.

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According to the datasheet P.4 6.4 Thermal Information,

RθJA of DRV(SON) package is 100.2°C/W and RθJC(top) is 108.5 °C/W.

I think Theta(j-a) is quite small and Theta(j-c) is too large.

Because Theta(j-a) is thermal resistance from junction to Ambient.

On the other hand RθJC(top) is junction to case(top), this is shorter.

Could you please let me know why.

Is the measurement method different?

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I appreciate your great help.

Best regards,

Shinichi

over 6 years ago

0 Ryan Eslinger over 6 years ago

TI__Guru 55940 points

Hi Shinichi,

The Thermal Information table is populated with metrics simulated on a JEDEC Hi-K board. The following Application Report discusses the thermal metrics and how they should be interpreted:

http://www.ti.com/lit/an/spra953c/spra953c.pdf

Please keep in mind that board layout will play a role in the thermal performance of a linear regulator. The following Application Report discusses the impact of board layout on LDO thermal performance:

http://www.ti.com/lit/an/slvae85/slvae85.pdf

Very Respectfully,

Ryan

0 Shinichi Inoue over 6 years ago in reply to Ryan Eslinger

Guru 21701 points

Hi Ryan,

Thank you for your reply.

The customer'd like to know why RθJC(top) 108.5 °C/W is larger than RθJA 100.2°C/W.

He thinks RθJC(top) should be smaller than RθJA.

I confirmed other device, regarding SON package, RθJC(top) is larger than RθJA.

I think this is quite normal for SON package, but I don't know the reason.

Could you please let me know why.

Due to the package structure?

Or measurement method has changed?

Or another?

I appreciate your great help.

Best regards,

Shinichi

0 Ryan Eslinger over 6 years ago in reply to Shinichi Inoue

TI__Guru 55940 points

Hi Shinichi,

The reason that the metrics are resulting in RθJC(top) being larger than RθJA is due to the material properties of the regulator and the measurement technique as described in the provided Application Report.

http://www.ti.com/lit/an/spra953c/spra953c.pdf

Very Respectfully,

Ryan

0 Shinichi Inoue over 6 years ago in reply to Ryan Eslinger

Guru 21701 points

Hi Ryan,

Thank you for your reply.

You mention about material properties, does this include mechanical structure?

I think the material is the same as the other packages, rather the difference is the mechanical structure.

Is it correct?

I appreciate your great help.

Best regards,

Shinichi

0 Shinichi Inoue over 6 years ago in reply to Shinichi Inoue

Guru 21701 points

Hi Ryan,

I've been considering this.

I could understand the reason measurement way changed.

I think measurement way of RθJC(top) is different from existing RθJC.

I appreciate your great help and cooperation.

Best regards,

Shinichi

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TLV755P: difference of thermal resistance between theta(j-a) and theta(j-c)