Two questions that are often asked when designing an operational amplifier into a new application are:
What is his "typical value" of power dissipation?
What is his "maximum" power dissipation?
In most cases, these issues are raised along with other issues related to the various thermal impedance characteristics of the device. These questions are part of the standard question bank used to measure the power handling capabilities of devices and help expose all possible long-term reliability issues.
An amplifier's data sheet may not list power dissipation information, but under normal circumstances, it does provide the operating voltage range, and the typical and maximum operating current. Normally, you can directly answer the first question about "typical" power values. Use the power formula, P DQ = V S ∙I Q , and that's it, where P DQ is the static power, V S is the supply voltage, and I Q is the "typical" static operating current.
We use the CMOS OPA316 operational amplifier as an example and calculate its "typical" power. The voltage range and operating current are provided in the data sheet below:
The voltage range is rated between +1.8 to +5.5V, and the typical value of I Q is 400μA. Figure 1 shows a simple measurement circuit. Assuming a nominal value of 5V power supply voltage, using V S ∙I Q , the "typical" power, P DQ , is 2mW. Simple enough!
1. FIG OPA316 configured to determine the static power dissipation
Since users do not often indicate the operating conditions, the maximum power situation is different. In most cases, it is left to application engineers to experiment and speculate on user needs. Do they require maximum power when the amplifier is operating in normal linear mode, or under certain extreme conditions?
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