ADUM3154: 3.75 kV, Dedicated Isolators for SPI Interfaces (with Control for up to 4 Slaves)

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ADUM3154: 3.75 kV, Dedicated Isolators for SPI Interfaces (with Control for up to 4 Slaves)

The ADuM3154 is a 3.75kV rms, 7-Channel, SPIsolator™ digital isolator optimized for a serial peripheral interface (SPI) that includes support for up to four slave devices. (5kV rms model available). Based on the Analog Devices, Inc., iCoupler® chip scale transformer technology, the low propagation delay and jitter in the CLK, MO/SI, MI/SO, and SS channels support SPI clock rates of up to 17 MHz.
The ADuM3154 isolator also provides a slave select multiplexing system that allows up to four slave devices to be serviced from one isolator. The slave select system propagates to the desired output with full propagation speed, allowing tight timing control. The isolated SS multiplexer is addressed through a 250 kbps low speed dual port with 2.5 μs of setup time.

APPLICATIONS

    • Industrial programmable logic controllers (PLCs)
    • Sensor Isolation

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Excellent product – with one catch

Overall, this product performed exactly as expected & needed for my project. However, I needed to isolate a set of ADC channels and DAC channels from each other, so I used 2 of these SPIsolators, giving me a total of 8 channels (using 2 master slave selects) split onto 2 seperate slave power rails. Individually, these chips work splendidly in giving me 4 channels per SS. However, when I multiplexed the chips on the master end by tying MOSI, MISO and SCLK to a single bus, I came to realize that the MISO line is driven by the chip even when SS is high. This is extremely frustrating since communication returned from one chip (MISO) is always subject to interference from the other chip. Even with the slave MISO lines tied low w/pulldown resistors, the master MISO line is driven and pulled low by the SPIsolator. I managed to get the system up and running with both chips by using resistors to force one chips MISO to reference the others as ground, but this is NOT ideal and I am unsure about its long-term viability.
This being said, if you need 4 isolated SPI channels, this chip is simply wonderful. Just expect trouble if you intend on multiplexing any further.

Reviewed by Willie on Analog Devices Product Page

 

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