Hi team，
Some power IC datasheet will have the Thermal Derating Curve which will show how the output current/output power change when temperature rise.
For example，tps82140 has the following curve.
However, I can't find the curve in TPS7A88-Q1/TPS7A8101-Q datasheet. How can I know the Power Derating about these socket? Does any other Parameter or curve also describe Thermal Derating?
Thanks a lot !
Hi Amelie,
This curve can be derived for the TPS7A88-Q1 with the θja parameter specified in the datasheet. Note that this LDO is a dual output device, so for these calculations I will assume both individual LDOs are being used equally. The junction temperature is therefore calculated as:
Tj = Ta + θja * (2*Pd)
Tj = junction temperature
Ta = ambient temperature
θja = junction-to-ambient thermal resistance
Pd = power dissipation of one TPS7A88-Q1 pass FET
After rearranging this equation to make Iout the dependent variable and Ta the dependent variable:
Pd,max = (Tj,max - Ta) / (2*θja)
Iout,max = (Tj,max - Ta)/(2*(Vin - Vout)*θja)
For this example I will use the following conditions:
Vin = 3.3 V
Vout = 1.8 V
Tj,max = 125 C
θja = 39.8 C/W
The thermal derating curve is the maximum rated output current (1 A for the TPS7A88-Q1) or the Iout,max calculation above, whichever is smaller. You can use graphing software like Excel to plot the curve across the recommended operating temperature. I have also attached the spreadsheet in which these conditions can be changed to see the effects on the curve.
Thanks,
Gerard
