Maxim Integrated MAX12900 Sensor Transmitter AFE
Maxim’s MAX12900 Sensor Transmitter Analog Front-End is an ultra-low-power, highly integrated 4-20 mA sensor transmitter for industrial applications. The MAX12900 is smaller, more accurate, and consumes less power than alternative solutions. It can work with any sensor transmitter but is designed for smart sensors with an integrated MCU providing a linear analog or PWM output. This input from the MCU is then converted into a current output for a 4-20 mA loop.
To do this accurately and efficiently, the MAX12900 integrates 10 building blocks including an LDO with a 4-36 V input, two PWM input conditioners, two low-power low-drift general purpose op-amps, one wide bandwidth zero-offset op-amp, two comparators, a low-drift voltage reference, and a power-up sequencer. These blocks can be connected in many ways to optimize the functionality and performance of the MAX12900 to the target application, and the IC consumes just 170 µA, which is 50% less than a traditional solution.
The blocks are used to form the equivalent of a 16-bit, high linearity digital-to-analog converter. The voltage reference has a max drift of 10 ppm/°C, which is 3.5 times better than competing solutions, and the IC can operate over a wide industrial temperature range.
One common implementation is to use 8-bit PWMs for coarse and fine adjustment of the output current. These PWMs are reshaped by the conditioners to provide a stable amplitude, and the outputs of the conditioners are summed and connected to one of the general purpose op-amps, which is configured as an active filter. This is equivalent to a 16-bit DAC. The filtered output is then fed to a wideband op-amp, which drives an external transistor to generate the loop current.
The MAX12900 is packaged in a 5 x 5 x 0.8 mm 32-pin TQFN for a solution size that is up to 50% smaller than alternative implementations. It supports 2-, 3-, and 4-wire configurations of the 4-20 mA loop, and offers diagnostic capabilities including supply rail monitoring, output current readback, open circuit detection, and failure detection.
For more details on Maxim’s MAX12900 and its evaluation board, visit Mouser.com.
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