EEVblog Electronics Community Forum
Electronics => Projects, Designs, and Technical Stuff => Topic started by: hobbyelectronics on August 25, 2024, 04:54:42 pm
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Hello,
Hopefully, this is a quick and easy question to answer.
I need to drive a stepper driver (Stepper Online CL42T-V4.1) with a ARM MCU based controller.
The DIR, ENABLE & PULSE inputs are optocoupled in the driver itself, and are 5V inputs (These do not work reliably at 3.3V, I tried it).
The data sheet states the input current (For each i/p) is 10 mA typical and 16mA Max.
I have a prototype circuit working using a SN74AHCT125 (8mA typical recommended o/p current, with 25mA Max continuous).
This was all I had to hand for testing, and looking at the data sheet is not really ideal, because if all stepper inputs (En, Dir, Pul) were at 16mA (worse case), this would not be supported the max current the 125 IC.
Anyway, my question really is what transceiver (or buffer) IC can I use which has a high enough output current.
I did find a single (SOT Package) single channel that fit perfectly, but I cannot remember the details. Most are 8mA or 12mA outputs.
Ideally, I would want a 1, 2 , or 4 channel device that can simply take my 3.3V MCU o/p and drive the opto input of the stepper driver at 5V (Max 16mA).
I Know I could use a MOSFET (x2 for non inverting) but an IC would be better for me in many respects. (Maybe Multiple BSS138's in a single package would work, but I am looking for a single IC)
Any thoughts or ideas about this or better still a part number of a suitable device (Not something like a a 244, but maybe a small footprint single of dual channel device).
Thanks
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74LVC1T45 (single) or ...2T45 (dual) bus transceivers. I would expect >24mA with about 0.5V drop @ 5V Vcc on the output side.
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Perfect.
That's exactly what I was looking for. Rated at 32mA so plenty of legroom.
Not sure why I couldn't find them when I was looking earlier today.
Thanks for your reply.
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you don't need two transistor per output, you can either do common gate/base for non inverting, or you can just use common source/emitter on the low side of the optocouplers
if the MCU can handle 5V in open collector mode you can also use that with 5V to the opto and driving with low side open collector directly from the MCU
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Hi.
I did consider using a transistor setup to control the LED on the opto input of the driver.
That's a good idea, but I do like the idea of using the IC to control the conversion from 3.3 to 5V and it gives me the option to swap out the drive for another make/model if required that may have a different input setup.
This way as long as its has a 5V i/p it should work.
Of course these are all excellent solutions, so thanks again for your replies.
Cheers
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Well if the 74AHCT125 works, then it should be fine.
Failing that, any 74ACT gate will do.
The 74ACT08/74HCT32 come to mind as they're non-inverting AND/OR gates.
https://www.onsemi.com/download/data-sheet/pdf/74act08-d.pdf (https://www.onsemi.com/download/data-sheet/pdf/74act08-d.pdf)
https://www.mouser.com/datasheet/2/149/74AC32-180325.pdf (https://www.mouser.com/datasheet/2/149/74AC32-180325.pdf)
If you need more channels, there's the 74ACT241.
https://www.ti.com/lit/ds/symlink/sn54act241.pdf (https://www.ti.com/lit/ds/symlink/sn54act241.pdf)
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Me only hobbyist, but:
I like to keep a dozen or so TI SN74LVC1T45DBV (https://www.ti.com/lit/ds/symlink/sn74lvc1t45.pdf) (4.06€ for ten at Mouser (https://mou.sr/3Xk71jg)) in SOT23-5 in stock, because it can source or sink 24mA, is fast, can do any voltage translation between 1.65V and 5.5V, and most importantly, is large enough for a hobbyist like myself to dead-bug: solder directly to wires and cover with heatshrink, even without a PCB.
A suitable adapter PCB is of course very easy to do at e.g. EasyEDA and order from JLCPCB/PCBWay/etc.
I've also used NXP NX138AK (https://assets.nexperia.com/documents/data-sheet/NX138AK.pdf)s (N-MOSFET) in SOT23-3 for open collector drive; it's very similar to BSS138, but faster (lower gate capacitance). This would require inverting the logic on the host, though. (I got a hundred of these from Mouser (https://mou.sr/3JeGj3O) for 5.30€, for logic type use cases, also dead-buggable.) In my experience, these are fast enough for most purposes, and the gate-source voltage can vary between +20V and -20V, which covers all my interfacing needs nicely. They conduct very well at about Vgs=2.5V, so are easy to use with 3.3V logic. I picked them when I first wanted to interface microcontrollers to standard 4-pin 12V PWM fans and tach signals. (25 kHz PWM, two tach pulses per revolution, open collector but with some pull-up requirements/suggestions.)
I also keep TI TXU0304 (https://www.ti.com/lit/gpn/txu0304) in TSSOP-14 in stock for SPI translation (0.79€ apiece at Mouser (https://mou.sr/3Mk8C25)), and it should work here too (the fourth, return signal, would be unused or free for you to use for other purposes), although its outputs are only rated at 12mA source/sink at 4.5V and higher (absolute maximum is 25mA continuous). For this, you'd need a TSSOP-14 adapter board or your own PCB, though, and I think three SOT23-5 (TI SN74LVC1T45DBVs) would make more sense anyways. The 0.65mm pitch is too dense for me to solder directly wires to, I definitely need a PCB for these.