Ultra-low power industrial, octal, digital input translator

The MAX31914 translates and conditions the 24V digital output of sensors and switches used in industrial, process, and building automation to 5V CMOS-compatible signals required by microcontrollers. It provides the frontend interface circuit of a programmable logic controller (PLC) digital input module.

The signal voltage translation is performed in conjunction with input current limiting and lowpass filtering. Input current limiting allows a significant reduction in power consumed from the field-supply voltage, as compared to traditional discrete resistor-divider implementations. To achieve the lowest in-class power dissipation, the IC uses patent-pending circuit techniques to achieve further reduction of power dissipation beyond what is possible by input current limiting alone. This special low-power operating mode is automatically activated when on-chip lowpass filtering is selected.

Selectable on-chip lowpass filters allow flexible debouncing and filtering of sensor inputs based on the application. When no filtering is selected, the IC is capable of detecting pulses as short as 0.75μs at its field inputs.

All 8 input channels are translated to CMOS logic levels and presented in parallel on the eight output pins for direct or galvanically isolated interface with a controller ASIC or micro.

The on-chip 5V voltage regulator can be used to power external optocouplers, digital isolators, or other external 5V circuitry.

For low-cost applications, Maxim Integrated offers a pin compatible version of this device, the MAX31915, which does not include the current-switching circuitry included in the MAX31914.