Part Details for ADR02 by Analog Devices Inc

The circuit features the AD8420, an instrumentation amplifier based on an indirect current feedback architecture. Because of this architecture, the AD8420 has excellent input and output characteristics. Unlike conventional instrumentation amplifiers, the AD8420 can easily amplify signals at or even slightly below ground without requiring dual supplies. The AD8420 has rail-to-rail output voltage swing that is completely independent of the input common-mode voltage. This exempts the AD8420 from the restrictions caused by interaction between the common-mode input and output voltage associated with most conventional instrumentation amplifier architectures. The flexible input and output characteristics, together with micropower consumption (80 μA maximum for 0 V input) and wide supply range, make the AD8420 ideal for flexible low power industrial applications.

The design provides a complete solution for the 4 mA-to-20 mA transmitter for pressure sensor measurements. The circuit has three critical stages: the sensor excitation drive, the sensor output amplifier, and the voltage to current converter.

For industrial control modules, standard analog output voltage and current ranges include ±5 V, ±10 V, 0 V to +5 V, 0 V to +10 V, +4 mA to +20 mA, and 0 mA to +20 mA. The AD5755-1 provides all of these ranges in a high precision, fully integrated, low cost, single-chip solution. A 20% overrange feature is also available for the voltage output ranges. Each DAC channel has a gain (M) and offset (C) register, which allow trimming the gain and offset errors of the entire signal chain.

The design provides a complete solution for the 4 mA-to-20 mA transmitter for pressure sensor measurements where the supply for the entire circuit is provided by the loop. The circuit has three critical stages: the sensor excitation drive, sensor output amplifier, and the voltage to current converter.