Which line driver should one use for XY2-100 and XY3-100?
Raylayse recommends in this manual to use
as a line **driver.**Note that each UA9638CD contains two separate driver circuits while you need five drivers (CLK, SYNC, X, Y & Z), so you need to use three UA9638CD chips to be able to drive a XY2-100 interface.
In general, any RS422 or RS485driver (with RS485 drivers being operated in fixed transmit mode with the driver being disabled) will do the job. However there are certain considerations:
- The driver must be able to operate at 15 MBaud / 15 MHz input speed. Some (although few) RS485/RS422 drivers are slew rate limited, i.e. they cannot drive any signal faster than X kBaud/MBaud. I recommend not to use a driver that is slew rate limited. Most RS485/RS422 drivers are able to drive 15 MBaud and this is fine for XY2-100.
- The driver should be able to withstand ESD surges, as usual in industrial equipment
- Only ever use drivers with internal short circuit protection. Almost all line drivers do that anyway, but it’s really important in guaranteeing the robustness of your equipment
- When using multiple separate driver chips, always use only one type of driver chip, as the receiver could experience skew between the different signals which might lead to bad received data. Never ever use different types of driver chips.
- In general, drivers driven by 5V instead of 3.3V (or even 1.8V) provide a higher current into a given resistance, leading to high signal to noise ratios, plus they are quite expensive. Use 3.3V or 1.8V RS485/RS422 drivers only if not possible otherwise, but always check if the logic level of the MCU driving the line driver fits the input logic level of the line driver.
My opinion is that you should go with the following specs for most products:
- Use three dual RS422 drivers with 15 MBaud speed capability
- Use drivers with 5V supply with 3.3V compatible logic level
- Use only drivers with at least ±8kV ESD (HBM), preferred ±15kV, and internal short circuit protection. These are reasonably robust.
My recommendation of finding a suitable receiver is to first search on the manufacturer’s websites because they provide more appropriate filters for this usecase:
- Texas Instruments
- ST Microelectronics
- Maxim Integrated
- Intersil
(it’s usually best to google for e.g. Texas Instruments RS422 to get directly to the correct page) and then check on Octopart etc if the part has sufficient stock quantities (at least 1k).
and, if searching on the manufacturer’s sites doesn’t yield any suitable result, search on DigiKey, Mouser and Farnell for other (typically smaller) manufacturers or different models that you might have missed.
In my case, I identified the Maxim MAX22508E as an excellent choice, since it supports high datarates up to 50 Mbps (leading to slightly more EMI but also possibly better signal integrity since the eye patterns is more open when using a much faster transceiver, leading to more accuracy in detecting the timing of the flank, leading to lower error rates). While it is somewhat expensive (2.50€/pc at small qtys), this is fine for many laser applications.