GENERAL DESCRIPTION

The AD8601, AD8602, and AD8604 are single, dual, and quad rail-to-rail, input and output, single-supply amplifiers featuring very low offset voltage and wide signal bandwidth. These amplifiers use a new, patented trimming technique that achieves superior performance without laser trimming. All are fully specified to operate on a 3 V to 5 V single supply.The combination of low offsets, very low input bias currents, and high speed make these amplifiers useful in a wide variety of applications. Filters, integrators, diode amplifiers, shunt current sensors, and high impedance sensors all benefit from the combination of performance features. Audio and other ac applications benefit from the wide bandwidth and low distortion.For the most cost-sensitive applications, the D grades offer this ac performance with lower dc precision at a lower price point.Applications for these amplifiers include audio amplification for portable devices, portable phone headsets, bar code scanners, portable instruments, cellular PA controls, and multipole filters. The ability to swing rail-to-rail at both the input and output enables designers to buffer CMOS ADCs, DACs, ASICs, and other wide output swing devices in single-supply systems.The AD8601, AD8602, and AD8604 are specified over the extended industrial (−40°C to +125°C) temperature range. The AD8601, single, is available in a tiny, 5-lead SOT-23 package. See the Ordering Guide for automotive grades.

FEATURES

Low offset voltage: 500 µV maximum

Single-supply operation: 2.7 V to 5.5 V

Low supply current: 750 µA/Amplifier

Wide bandwidth: 8 MHz

Slew rate: 5 V/µs

Low distortion

No phase reversal

Low input currents

Unity-gain stable

Qualified for automotive applications

 

APPLICATIONS

Current sensing

Barcode scanners

PA controls

Battery-powered instrumentation

Multipole filters

Sensors

ASIC input or output amplifiers

Audio

 

THEORY OF OPERATION

The AD8601/AD8602/AD8604 family of amplifiers are rail-to-rail input and output, precision CMOS amplifiers that operate from 2.7 V to 5.0 V of the power supply voltage. These amplifiers use Analog Devices, Inc., DigiTrim technology to achieve a higher degree of precision than available from most CMOS amplifiers. DigiTrim technology is a method of trimming the offset voltage of the amplifier after it has been assembled. The advantage in postpackage trimming lies in the fact that it corrects any offset voltages due to the mechanical stresses of assembly. This technology is scalable and used with every package option, including the 5-lead SOT-23, providing lower offset voltages than previously achieved in these small packages.

The DigiTrim process is completed at the factory and does not add additional pins to the amplifier. All AD860x amplifiers are available in standard op amp pinouts, making DigiTrim completely transparent to the user. The AD860x can be used in any precision op amp application.

The input stage of the amplifier is a true rail-to-rail architecture, allowing the input common-mode voltage range of the op amp to extend to both positive and negative supply rails. The voltage swing of the output stage is also rail-to-rail and is achieved by using an NMOS and PMOS transistor pair connected in a common-source configuration. The maximum output voltage swing is proportional to the output current, and larger currents limit how close the output voltage can get to the supply rail, which is a characteristic of all rail-to-rail output amplifiers. With 1 mA of output current, the output voltage can reach within 20 mV of the positive rail and within 15 mV of the negative rail. At light loads of >100 kΩ, the output swings within ~1 mV of the supplies.The open-loop gain of the AD860x is 80 dB, typical, with a load of 2 kΩ. Because of the rail-to-rail output configuration, the gain of the output stage and the open-loop gain of the amplifier are dependent on the load resistance. Open-loop gain decreases with smaller load resistances. Again, this is a characteristic inherent to all rail-to-rail output amplifiers.