Is Your Amplifier Disabled, or is it Merely Sleeping?


What’s the difference between, power-down, shutdown, standby, sleep mode or disable?

RAQ:  Issue 59


While all these functions may sound similar, they can have very different meanings depending on the specific amplifier and the manufacturer.

We use the terms power-down and shutdown to represent the state of an amplifier when the quiescent supply current is lowered from its normal operating level. The supply current is typically throttled back by reducing the current in the amplifier's internal bias circuitry. For example, an amplifier that draws milliamps of quiescent current in normal mode may draw only microamps or even nanoamps in power-down mode. The amplifier’s output voltage is undefined in both power-down and shutdown modes.

We use the term disable to represent the state of an amplifier whose quiescent supply current is reduced from the normal on state of the amplifier, but with the additional feature that the output goes to a high-impedance state when the device is put into disable mode. This extremely useful condition provides high input-to-output isolation, and enables outputs to be multiplexed by wire or'ing them together.

Read the data sheet carefully. For a simple power-down function, the specification table may contain a couple of lines that discuss the power parameters, or there may be a plot of normal vs. power-down supply current. There may also be a plot of the power-down current over temperature. For a disable function (high-impedance state), you can expect the same specification table references, but you may also find an output impedance vs. frequency plot–as the high output impedance is not constant over frequency–or a circuit example featuring the high-impedance capability of the device in a multiplexed application. Also be careful to note the power-down threshold voltages. Op amps do not have ground pins, so most power-down circuits are internally referenced to one of the supply rails. The switching levels may not be compatible with conventional logic signals and may thus require some type of level translation.

Not all manufacturers use the same naming convention; what one manufacturer calls disable another may call shutdown, so you should consult the manufacturer's data sheet for their definition of powerdown, shutdown, or disable.


John Ardizzoni

John Ardizzoni

John started at Analog Devices in 2002, as an Application Engineer in the High Speed Amplifier group. Prior to joining Analog Devices John worked for IBM, in RFIC applications and at M/A-COM for 20 years. John is also co-author of Analog Devices Rarely Asked Questions (RAQ's) column. John has over 30 years experience in the electronics industry, and has authored numerous articles and design ideas.