IC heat disipation calculations

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Hi All,

I am looking for heat disipation theory and calculations.

I have a dc-dc NCP3063 switching regulator in a SOIC pakage and I am =
trying to get a handle on the heat disipation calc's becuase I suspect =
it is over heating and shutting down.
data sheet here =
http://www.onsemi.com/PowerSolutions/product.do?id3D%NCP3063PG

SOIC-8     Thermal Resistance Junction-to-Air  R04%JA 180   B0%C/W

24v in     12V out  Bucket design



Any pointers would be appreciated

Joe






Re: IC heat disipation calculations
On Thu, 6 Sep 2007 00:06:36 +1000, "Joe G \(Home\)"

Quoted text here. Click to load it
get a handle on the heat disipation calc's becuase I suspect it is over heating
and shutting down.
Quoted text here. Click to load it

Some chip makers (National, Texas, Linear) have good downloadable app
notes on heat sinking.


D from BC

Re: IC heat disipation calculations
On Thu, 6 Sep 2007 00:06:36 +1000, "Joe G \(Home\)"

Quoted text here. Click to load it
get a handle on the heat disipation calc's becuase I suspect it is over heating
and shutting down.
Quoted text here. Click to load it

How hot does the top of the package get? Does freeze spray fix the
shutdown?

Glue a heatsink to the package and see if that helps.

What's your output current?

What is "Bucket design"?

John


Re: IC heat disipation calculations
Quoted text here. Click to load it
s over heating and shutting down.
Quoted text here. Click to load it

I don't understand the question.  The package has a 18020%
degree C temperature rise above ambient for each watt it20%
dissipates.  Board layout can alter this a bit, since the20%
copper traces are the main path for heat to escape the chip.

By Bucket design, I assume you mean buck converter.

What output current is this chip supplying?

Is the chip being heated by proximity to the output diode?

Re: IC heat disipation calculations
On Thu, 6 Sep 2007 00:06:36 +1000, "Joe G \(Home\)"

Quoted text here. Click to load it
get a handle on the heat disipation calc's becuase I suspect it is over heating
and shutting down.
Quoted text here. Click to load it

Something along the lines of:

Pd~= (Vin * Icc) +  (VSWCE(DROP) * Iswitch(avg) * ton/(ton + toff))

Should come close (although it ignores losses during the darlington
switching, so actual losses are going to be higher).
VSWCE(DROP) is 1.3V max., 1.0V typical. Icc is 7mA max.

The SOIC package is not very good for power dissipation.

Best regards,
Spehro Pefhany
--
"it's the network..."                          "The Journey is the reward"
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