Ultra-Low-Power 4-20mA Sensor Transmitter

The MAX12900 is an ultra-low-power, highly integrated 4-20mA sensor transmitter. The MAX12900 integrates ten building blocks in a small package: a wide input supply voltage LDO, two conditioner circuits for pulse-width modulated (PWM) inputs, two low-power, low-drift, general purpose operational amplifiers (op amp) one wide bandwidth, zero-offset drift operational amplifier; two diagnostic comparators, a power-up sequencer with power good output to allow for a smooth power-up, and a low-drift voltage reference.

The MAX12900 converts PWM data from a microcontroller into current over a 4-20mA loop with two, three, or four wire configurations.

The equivalent to an ultra-low-power, high-resolution, digital-to-analog converter is realized with the combination of two-PWM signals received from a microcontroller, the two conditioner circuits, and an active filter built with the integrated low-power op amp. The outputs of the two conditioner circuits provide a stable PWM amplitude over voltage supply and temperature variation. The wide bandwidth amplifier, in combination with a discrete transistor, converts a voltage input into a current output and allows HART and Foundation Fieldbus H1 signal modulation. The zero-offset operational amplifier and the low-drift voltage reference provide negligible error over wide temperature. The low-power operational amplifier and comparators provide building blocks for enhanced diagnostic features. Supply rail monitoring, output current readback, open circuit and failure detection are a few examples of diagnostic features. All these features, as well as ultra-low-power and high accuracy make the MAX12900 ideal for loop-powered smart sensor transmitters for industrial application.

The MAX12900 is available in 5mm x 5mm 32-pin TQFN package and operates over a wide industrial temperature range of -40°C to +125°C.

Applications

* Industrial Automation and Process Control * Loop-powered 4-20mA Current Transmitter * Remote Instrumentation * Smart Sensors

* Wide Input Supply Range: 4.0V to 36V

* Ultra-Low-Power Consumption: 170μA (typ)

* High Linearity: 0.01% (Max Error)

* High Resolution: Up to 16 Bit

* Low Drift Voltage Reference: 10ppm/°C max

* Wide Temperature Range: -40°C to +125°C

* Small Package: 5mm x 5mm x 0.8mm 32-pin TQFN