AD694ARZ

The AD694ARZ is one member of the AD9381 series.The AD694 is a monolithic current transmitter that accepts high level signal inputs to drive a standard 420 mA current loop for the control of valves, actuators, and other devices commonly used in process control.The input signal is buffered by an input amplifier that can be used to scale the input signal or buffer the output from a current mode DAC. Precalibrated input spans of 0 V to 2 V and 0 V to 10 V are selected by simple pin strapping; other spans may be programmed with external resistor.

Features of the AD694ARZ are:(1)420 mA, 020 mA output ranges; (2)precalibrated input ranges:0 V to 2 V, 0 V to 10 V; (3)precision voltage reference programmable to 2.000 V or 10.000 V; (4)single or dual supply operation; (5)wide power supply range: +4.5 V to +36 V; (6)wide output compliance; (7)input buffer amplifier; (8)open-loop alarm; (9)optional external pass transistor to reduce self-heating errors; (10)0.002% typ nonlinearity.Active laser trimming of the AD694's thin film resistors results in high levels of accuracy without the need for additional adjustments and calibration. An external pass transistor may be used with the AD694 to off-load power dissipation, extending the temperature range of operation.

The absolute maximum ratings of the AD694ARZ can be summarized as:(1)junction temperature range:300;(2)storage temperature range:-65 to 150;(3)case temperature:150;(4)supply voltage:36V;(5)input voltage:-0.3 to 36V;(6)alarm voltage:36V.The AD694 can operate as a stand-alone 420 mA converter with no additional active components. However, provisions have been made to connect IOUT to the base of an external NPN pass transistor as shown in Figure 4.This permits a majority of the power dissipation to be moved off-chip to enhance performance and extend the temperature range of operation. Note that the positive output voltage compliance is reduced by approximately 0.7 V, the VBE of the pass device. A 50 resistor should be added in series with the pass transistor collector, when the AD694 is operated with dual supplies, as shown in Figure 4.This will not reduce the voltage compliance of the output stage.