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Universal line driver for differential and single ended usage?

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Manx:
I need a line driver that could be used for both differential and single ended operation. All I can find are RS485 compatible drivers, that are not good for single ended operation, and RS422 drivers that would be OK concerning voltage levels, but their current is limited to 20 mA, and I'd like to have at least 50 mA.

I'm thinking of simply using two single ended line drivers, non-inverting and inverting. This would probably be the cheapest and would save me from spending further days looking for a suitable IC. However, I don't know how bad it would be if I do it in such way.

Output from my device will go into servo motor drivers. Normally it will be just driving a led, but I'm wondering what would happen if the servo motor driver had a "proper" differential receiver; how bad my non-standard approach be in that case. Also, I'm wondering what using two ICs as a substitute for a differential driver would do to EMI.

T3sl4co1l:
What's wrong about RS-422/485 drivers for single-ended operation?  Just leave one channel open. :)

Could also wire together a few logic buffers in parallel, or use a small gate driver.  Neither of these are slew-rate controlled for EMI, of course (preferably, the signal should be carried in coax).

What do you mean driving an LED?  Like an optoisolator?  Or just for indication?  How many?  How fast?  Is this just low frequency PWM for RC servos?  Do you really need much current drive?

What distance, and what kind of cabling?  Do you need a common ground or no?

Tim

Manx:
RS485 gives too big output low voltage. On the other hand RS422 gives only 20 mA.

Yes, I mean driving one led in an optoisolator. One microsecond rising/falling edge should be enough, I think, although I don't mind having it faster. It's for industrial servo drivers. I think 50 mA would give me some headroom just in case. One servo driver I checked takes 20 mA on an input; I don't want to be at the limit.

Distance max 2 meters. Need for a common ground will depend on the servo driver. I want to provide an universal output.

SiliconWizard:
Uh huh, not too sure about what the problem is exactly either.

As an obvious side note, you could just have two separate output drivers, one differential, the other not (and possibly with higher current for the single-ended one if I got it correctly), both fed by the same digital input signal? They could go to separate connectors as well, as using a single connector for both modes could be confusing for the end-user.

Except if your design is ultra cost-constrained, really... I wouldn't bother doing it another way. Especially if you intend on driving standard RS-485 receivers, which may be what you're implying with "proper differential receiver". Better use standard drivers so they are conforming.

Just a thought, we don't know squat about your application, so...


Manx:
It's for a motion controller.

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