Junction Temperature

Find junction temperature of the Texas Instruments OPA2134P4 op-amp chip when powered-on but not driving a load ($V_{out}A,B = 0). (10 bonus points) Assume power supply voltages of +/-15 V, ambient temperature TA = 30°C, and the system has reached thermal equilibrium with no heat sink attached. This particular model has two amplifiers on the chip and uses an 8-pin DIP package. First find the total power supplied to the entire packaged unit. Clearly state the origin of your numbers, and your calculation procedure. Failure to do so is an invitation to receive less points.

Answer

In the data sheet in the Power Supply specifications we have

Operating Voltage =+/-15 V (differential voltage)

Quiescent current per amplifier (by definition current drawn by the amplifier when it is not amplifying and with no load) I = 4 mA

(These are the typical values. )

Thus the power consumed per amplifier with no load is $P=U*I =(15+15)*0.004 =0.12 W$

Power for 2 amplifiers is $P =2*0.12 =0.24 W$

The thermal resistance for 8 pin-DIP package (from data sheet)

R =100 (deg Celsius/ W)

By definition $R = \Delta(T)/P$ so the temperature difference between the ambient and the junction is

$\Delta(T) = P*R =0.24*100 =24 deg.C$

For an ambient temperature of let $30 deg.C$ ($86 F$) the temperature of the junction will be

Tj =24+30 =54 degree Celsius