Overview

Description

This is a reference design of a system that incorporates 4 pieces of RX23E-A with channel-to-channel isolation and measures temperature and voltage synchronously. This is ideal for applications, such as analog input module with multiple analog inputs, temperature controller, recorder, and data acquisition.

This is a reference design combining high precision AFE mounted MCU 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 quantity. This allows high precision measurement, high speed response, and 4ch 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. 4ch synchronous measurement can be realized within 1msec. These specifications appear to be adequate for the system that processes signal changing relatively slowly, such as temperature and pressure.   

Communication between 4 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 comparing to 4-wire SPI communication which uses chip select.

To isolate communication, CMOS output photocoupler RV1S9260A and 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 output of RX23E-A is High or Hi-z. As a result, 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.

Features

  1. High precision AFE mounted MCU RX23E-A on the edge side.
    • RX23E-A performs distributed processing, such as digital filter processing and conversion of physical quantity.
    • Distributed processing can reduce the load of host MCU.
  2. 4ch with channel-to-channel isolation enables measurement of temperature and voltage.
    • Enable 4ch synchronous measurement within 1msec
    • Measurement result acquisition cycle 10msec
    • High speed response, step response 70msec
  3. Adopt 3-wire serial communication for communication with host MCU RX72M.
    • Enable reduction in the number of isolators compared to 4-wire SPI communication using chip select.
  4. Isolated power supply is configured with a synchronous buck regulator ISL85410.
    • Using isolation transformer with 1 input 2 output can realize 2ch of isolated power supply.

Components

  • Application note
  • Circuit diagram (included in application note)
  • BOM (included in application note)
  • Gerber file
  • RX23E-A sample program
  • RX72M sample program

Applications

Design & Development

Sample Code

Related Boards & Kits

Boards & Kits