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questions on op amp power dissipation – Part 1

Top questions on op amp power dissipation – Part 1

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Top questions on op amp power dissipation – Part 1

Thomas Kuehl

Jul 30 2014 11:30 AM

Comments 0

Two commonly asked questions when designing an operational amplifier into a
new application are:

What is its “typical” power dissipation?

What is its “maximum” power dissipation?

Most often these questions are asked in conjunction with other questions
regarding the device’s various thermal resistance characteristics. These are
part of a standard bank of questions used to gauge a device’s power-handling
capability and help disclose any potential long-term reliability concerns.

An amplifier’s data sheet may not list power dissipation information, but
usually it does provide the operating voltage range, and typical and maximum
operating currents. Answering the first question about “typical” power is
normally straightforward. It is a matter of applying the power formula,
PDQ = VS∙IQ,
where PDQ is the quiescent power, VS is the
supply voltage and IQ is the “typical,” quiescent operating
current.

Let’s use the CMOS OPA316 operational amplifier as an example and calculate its
“typical” power. Its voltage range and operating current are provided in the
data sheet as shown here:

The supply range is specified as +1.8 to +5.5 V, with a typical
IQ of 400 μA. Figure 1 shows a simple measurement circuit.
Assuming a nominal, 5 V supply voltage and applying
VS∙IQ, the “typical” power,
PDQ, is 2 mW. Easy enough!

Figure 1 OPA316 configured to determine quiescent power
dissipation

Maximum power is a different story because customers don’t often state the
operating conditions. Quite often it is left to the applications engineer to try
and surmise what the customer wants. Do they need the maximum power when the
amplifier is operating in a normal linear mode, or in some extreme
condition?

This will be the subject of Part 2 of this blog series. Our discussion will continue
soon on maximum power dissipation, but please subscribe to ensure you don’t miss
our next segment of this blog!

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$post.CommentCount)

operational
amplifier, op
amp, OPA316,
CMOS,
power
dissipation

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