The theraml analysis in IC design

[chang830]

Hi,
The circuit I am designing need to have hgh drive capability. In layout, I put the driver transistors compact to inprove the matching charateristics. But I found the thermal intensity is high to 200W/cm^2 for the area of compact driver transistors.

I have the concern the heat will brings the reliabilty for my IC.

Any guideline on the restriction for the heat on chip?

Thanks

 

[Vamsi Mocherla]

Try and put a temperature detection loop for the circuit so that I can operate in the lower current mode when the temperature exceeds a certain value.

Layout wise, you can actually try and spread the transistor to different corners of the chip. But this will cause a routing overhead and also a substantial IR drop if thick metal is not used.

Externally please put the provision for a heat sink for the place where the drivers are.

Added after 7 minutes:

By the way, are you sure about the numbers because 200W/cm^2 is hot bulb numbers.......

 

[chang830]

By the way, are you sure about the numbers because 200W/cm^2 is hot bulb numbers.......

Hi Vamsi,
Thanks for the reply.It is very helpful to me.

As for the 200W/cm^2 power density, that's waht I am being confused in present.

My 1st question is what is the uplimit for power density for convetional silicon chip?

Second, how to compute the power density in design phase? I used the current throught the transistor divided by the area the transistor occupying, which leads high up to surprisingly 200W/cm^2. Any wrong with it?

Thanks in advance for the help!

 

[Vamsi Mocherla]

Dear Chang,

Typical Modern microprocessors take about 45 -65 W/cm^2 in today's technologies. Refer to Intel's Power group which has all the facts on their websites. Another good reference is **broken link removed**
That was the reason why I said that your circuit is a hot bulb.

May be you must have computed by the equation power density = V*I/area of the transistor., where V is the power supply voltage and I the rms current. You should also try to factor in the duty cycle of switching in case of a switch or the 2*Vdsat of the the device, if it is operating in saturation.

I am sure that your pass transistors or power transistors in a voltage regulator will have higher power densities. Hence they are laid out at the periphery of the chip to alleviate thermal issues and IR drops.

I hope this helps

 

[qutang]

I think larger pass element will be fine.