Isolated RS422 chip selection

Question

I want to select an isolated full-duplex RS422 chip with a working rate of greater than or equal to 10 Mbps. I have looked at the ADM2561E/ADM2563E/ADM2565E/ADM2567E series of chips. I would like to know whether external power supply is required, or whether VISOIN and VISOOUT can be connected to ground through capacitors or ferrite beads? Since my front-end interface board only has two IO signals for me, can I connect the DE, /RE and other pins to a fixed level according to the application? However, will there be a risk of overheating when the chip is not communicating? 
 Can ADM2561E/ADM2563E/ADM2565E/ADM2567E realize RS422 function like ADM3252EABCZ, that is, realize RS232 communication with only TX and RX two IO signals? 
 Thank you.

ericb · Accepted Answer

It sounds like you are implementing a point to point RS-422 network with two nodes, each of which will have a Tx and Rx port. In this case, you would want to tie DE high and /RE low so that both of their ports are always active. Since DE and /RE are fixed, you only need I/O pins for the TxD and RxD signals. 
 I don't expect that the transceiver will overheat when not communicating; however, bringing DE low when not transmitting will reduce the power consumption. Note that when DE goes low, the output driver circuit will go high impedance and so you'll want to make sure that there is something to bias the bus so that the receiver maintains the proper state. 
 The ADM2561E and ADM2565E are half-duplex transceivers and their Tx and Rx ports are connected together for a single bus. The ADM2563E is a full duplex transceiver with separate Rx and Tx ports and so could be used for data rates up to 500kbps. Since your application needs at least 10Mbps, you would want to use the ADM2567E. 
 Depending on your isolation voltage requirements, you may also want to consider either the ADM2582E or ADM2682E.)

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Isolated RS422 chip selection