In my costume electronic card I have a half-duplex, ~12Mbps, RS485/RS422 Transceivers, LTC2862-1 device with 3.3Vbus. Now I want to connect to another, external LTC2862-2 device with 5Vbus (with max baud rate of ~115200bps which is O.K for both devices).
My question is that: Is it possible to connect those two devices without enable any self-protection mechanism of ether devices- in order to maintain the max devices ratability? (3.3V Vbus device that interface with 5V Vbus device and high baud rate device that interface with limited baud rate device)
Both the LTC2862-1 and LTC2862-2 have a receiver up that receive data at up to 20Mbps. Your application should work without issue, the LTC2862-2 will be able to receive the 12Mbps data from the LTC2862-1, and transmit 115200bps data back.
Both the transmitter and receiver have a wide common mode range of +25V to -25V, so there will be no issue connecting a 3.3V device to a 5V device, once you have terminated the bus.
First, thank you for your quick response!
Just for me to be sure, you mentioned that there will be no issue when connecting a 3.3V device to a 5V device duo to the common move voltage range. Isn't it true to say that the main concern when connection those two devices with two different VCC's will be the differential voltage rather the common mode voltage?
Thanks for your query. While it's true that the 5V RS485 device will drive a higher differential voltage onto the bus than a 3.3V device, the LTC2862 receiver can handle the differential voltage from a device powered from either supply voltage. A 3.3V powered LTC2862 can still accept the differential output voltage from a 5V powered LTC2862, and vice versa. In the RS485 standard a maximum of 5V differential output voltage is permitted.
In the case where both transceivers are transmitting at the same time on the bus, the LTC2862 transmitter outputs are short circuit protected to limit the current and prevent device damage during this fault condition. This is as per the RS-485 standard.