Analog Devices announced release of the AD859x family of low-cost, single-supply operational amplifiers, which offer the highest output (ý250 mA) and lowest shutdown (1 ýA) currents. The AD859x output current is more than three times that of the nearest competitive op amp, while the shutdown current is less than half that of the nearest competitor. High output currents directly drive many audio system outputs such as cellphone handsets, headphones or small speakers in desktop and portable PC's. Low shutdown current extends operating time in battery-powered systems.

The new single AD8591, dual AD8592 and quad AD8594 are fully specified for operation in 2.7-V to 5-V systems. Rail-to-Rail capabilities maximize the input- and output-signal range for accurate signal transmission in modem-data and telephony-signal applications. Even with a 5-V/ýS slew rate and 3-MHz gain-bandwidth product, the parts are stable with virtually any capacitive load, easily driving hundreds of nF with no fear of oscillation.

These amplifiers are particularly well suited for portable audio applications, such as cell phone handsets and headsets, PC audio, sound ports and sound cards. High output current is also great for line driving applications, such as modems, PBX, line cards, computer telephony, set top boxes and portable instruments.

For data acquisition system manufacturers looking for low-cost solutions, an inexpensive sample-and-hold circuit can be constructed with a single external capacitor by taking advantage of the high impedance output in shutdown mode. High output current quickly charges a wide range of capacitor values for fast acquisition time while low output leakage current over the full operating temperature range minimizes droop rate.

When should an op amp be called an audio amplifier these days? Or should we reserve the audio amplifier handle for things that produce amps instead of milli-amps? (That was an intended pun.) For applications where the listener is really not concerned about overall audio specifications this use of op amps is, I think, perfectly legitimate. These singles, duals and quads from Analog devices stand out for the extremely high drive level they achieve and will be quickly adopted in portable phones and PC audio equipment. The price is also right on the money for those applications.

It would be very difficult for a designer to get an audio circuit wrong with this part and I love the notion of using it as a low-cost sample-and-hold relying on the high-impedance of the output in shutdown -- which is, by the way, a rather nice number itself.