RX23E-A Channel-to-Channel Isolated Analog Input Module Reference Design

This is a reference design of a system that incorporates four pieces of RX23E-A with channel-to-channel isolation and measures temperature and voltage synchronously. This is ideal for applications, such as an analog input module with multiple analog inputs, a temperature controller, a recorder, and data acquisition.

This is a reference design combining high precision analog front-end (AFE) mounted MCUs RX23E-A and RX72M. RX23E-A performs not only A/D conversion but also distributed processing, such as digital filter processing and conversion of physical quantities. This allows high-precision measurement, high-speed response, and 4-channel synchronous measurement, which have not been realized by the existing discrete ADC before. In addition, the processing load of the host MCU RX72M is reduced so that RX72M focuses on processing that can be performed only by the host.

The cycle of measurement result acquisition is 10msec, and the step response time is 70msec. 4-channel synchronous measurement can be realized within 1msec. These specifications appear to be adequate for the system that processes the signal changing relatively slowly, such as temperature and pressure.   

Communication between four pieces of RX23E-A and RX72M is performed by a single-channel 3-wire serial communication, and individual communications with the specified unit address and the broadcast communication are performed. This can reduce isolators compared to 4-wire SPI communication, which uses a chip select.

To isolate communication, the CMOS output photocoupler RV1S9260A and the open collector output type photocoupler PS9124 are used. RV1S9260A is used for SCK and MOSI. PS9124 is used for MISO. The open collector output type photocoupler PS9124 is Hi-Z when the output of RX23E-A is High or Hi-Z. As a result, the MISO communication line is not occupied and available for bus communication.

The isolated power supply is configured with a synchronous buck regulator ISL85410 and an isolation transformer with 1 input 2 output.  In this configuration, 2 channels of isolated power supply are provided with a single power supply IC and a transformer.