How to estimate dissipated heat

[logancane]

Hi everyone,

Is there a general method of estimating how much heat power an IC chip must dissipate for a given load? I don't want to use a temperature estimation because I know that the assumptions they make in the datasheets on convection flow and on ambient temperature are different to my situation.

My first thought was to find an equivalent series resistance and use (I)^2*R to work it out, but there seems to be no reference to an IC ESR for most chips.

If it helps, these are the chips in question, but really I'm looking for a method that I can use on most types of IC's (in the same way that you can bet most datasheets will have reference to thermal resistance).

https://www.ti.com/lit/ds/symlink/lm5117.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1621639942217&ref_url=https%253A%252F%252Fwww.digikey.co.nz%252F

https://www.ti.com/lit/ds/symlink/tps2663.pdf?HQS=dis-dk-null-digikeymode-dsf-pf-null-wwe&ts=1621639925302&ref_url=https%253A%252F%252Fwww.digikey.co.nz%252F

Any help would be much appreciated!


 

[amyk]

P = IV

Edit: nevermind, I see they are switching ICs. In which case the power dissipation will be proportional to the on resistance of the MOSFET.

[cortex_m0]

The LM5117 is a controller, so there is no way to calculate power dissipation without completing the design. The gate drive will make a significant difference, which depends on the MOSFET you select. It is possible to calculate and sum the losses, and many simulation tools will allow you to do so as well. I think TINA-TI is among them, although I rarely use it.

EDIT: Linear Technology App Note 140 goes into how to calculate this by hand for both linear regulators and SMPS. https://www.analog.com/media/en/technical-documentation/app-notes/an140.pdf

The TPS2663x does specify the Pass transistor resistance in several conditions on Page 8. The power dissipated in the chip, to a decent approximation is I**2 * Ron + VIN_SYS * IQ(on).