TPS75801 Heat Sink Area

Hi Go,

It means the area taken up by the copper ground plane in figure 27. If your copper ground plane is 1 inch by 1 inch and you have no air flow your RthetaJA is about 35C/W, so if your maximum ambient temperature is 55C you can dissipate 2W of power over the device (and the LDO's junction temperature will be approximately 125C).

Regards,
David

Hi, David

Thank you for your comment.

Regarding your comment, It might be 1cm by 1cm copper ground plane for 2W dissipate capability

under the condition , no air flow ,ambient temperature is 55C?

Thanks

Go

Hi Go,

Nice catch on the units - it is 1cm by 1cm. Under the conditions above the maximum ambient temperature is 55C as there is a large rise in junction temperature. I would advise trying to stay quite a bit under this limit as high temperatures (125C) are known to decrease the lifespan of the IC.

Regards,

David

Hi, David

Thank you for your comment.

please let me know about Figure27 in TPS75801 D/S in a little more details.

1. Is the area indicated in red also copper plane? if yes, what is the area of it?

  (Please see the attached file)

2.Are the area indicated in green also thermal vias? 

   It doesn't seem to connect to Copper Solder Pad on top side, is it right?

  (Please see the attached file)

Thanks

Go

Hi Go,

(1) Area in red is also copper plane, but that plane typically includes signal traces and other components so the area is not stated. The general rule is more copper area directly beneath the device the better.

(2) They are also thermal vias and they are connected to the copper plane around the solder pad, but they do have soldermask over them.

Regards,
David

Hi, David

As for your answer (2), I suppose it's like the attached file, is it correct?

and does the area of the copper plane on the top layer stated?

Thanks

Go 

Hi Go,

That is correct and the area is not specified - you want as much of a top copper square as possible while still maintaining good design practices for DFM. As rules and guidelines vary depending on your PCB house we do not specify a top area.

Regards,
David