MLT isolated SPI Module

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Web site:

http://www.maleetronic.com/boardsprojects/mlt-iso-spi-module/

Project Summary:

A small breakout board based on the LTC 6820.

Full Project:

The isolated SPI Board is a small pcb module based on Linear’s LTC6820. The iso SPI module is designed for applications, where SPI signals need to be transferred over longer distances than usually. Especially when there is a noisy environment. It is based on Linear’s LTC6820. The board is designed as two layer stack-up, with GND plane on the bottom side of the PCB, and signals and components on the top layer. Signals and power are supplied over standard 100 mil (2.54mm) pitch IDC header.

The LTC6820 provides bidirectional SPI communications between two isolated devices through a single twisted-pair connection. Each LTC6820 encodes logic states into signals that are transmitted across an isolation barrier to another LTC6820. The receiving LTC6820 decodes the transmission and drives the slave bus to the appropriate logic states. The isolation barrier can be bridged by a simple pulse transformer to achieve hundreds of volts of isolation.
The LTC6820 drives differential signals using matched source and sink currents, eliminating the requirement for a transformer center tap and reducing EMI. Precision
window comparators in the receiver detect the differential signals. The drive currents and the comparator thresholds are set by a simple external resistor divider, allowing the system to be optimized for required cable lengths and desired signal-to-noise performance.

Board Features:

• 1 Mbps Isolated SPI Data Communication at 10m
• 0.5 Mbps Isolated SPI Data Communication 100m
• Galvanic Isolation Barrier using standard transformer (1500V)
• Board can act as Master or Slave selectable via on board jumpers
• On-board power supply 3.3V LDO or user supply voltage level for digital signals
• On-board SPI mode select
• Dimension: 40 mm x 30 mm (1.575″ x 1.185″)

Circuit diagram: