Need Help!- Running TWO Gecko 251's from one out put

[Mr.Chips]

I would like to know if it is OK to run two Gecko 251’s from one output of a Candcnc MTA 100 controller. Please see drawing.

Thanks
Hager

[bharbour]

It is hard to tell. From looking at CandCNC's docs, they don't show an output current capability for the step and direction signals. The only way to connect the Geckos is by paralleling the step and direction signals from the two drives because the step and direction signals share a common +V. Probably will have to email the folks at CandCNC and ask about the output drive on the ports. The Geckos each want about 6mA for step and direction as I remember, so you will need at least 12mA of current sinking capability. Double that would be nice for some margin.

Good Luck,
Bob

[dan_the_welder]

Originally Posted by bharbour It is hard to tell. From looking at CandCNC's docs, they don't show an output current capability for the step and direction signals. The only way to connect the Geckos is by paralleling the step and direction signals from the two drives because the step and direction signals share a common +V. Probably will have to email the folks at CandCNC and ask about the output drive on the ports. The Geckos each want about 6mA for step and direction as I remember, so you will need at least 12mA of current sinking capability. Double that would be nice for some margin. Good Luck, Bob

Hi,
I have been doing this for a while and it works fine. Look up the data sheet for the optos on the the CandCNC board. Check the current rating and if the numbers work, you are in.

I seem to remember that it was close in my application, Centent CNO143 drivers, but I went for it since I figured worst case I would have to replace the optos.

Again, I am doing this and it works great.

Dan

[Mr.Chips]

Originally Posted by bharbour It is hard to tell. From looking at CandCNC's docs, they don't show an output current capability for the step and direction signals. The only way to connect the Geckos is by paralleling the step and direction signals from the two drives because the step and direction signals share a common +V. Probably will have to email the folks at CandCNC and ask about the output drive on the ports. The Geckos each want about 6mA for step and direction as I remember, so you will need at least 12mA of current sinking capability. Double that would be nice for some margin. Good Luck, Bob

Thanks Bob,

Does anyone know if the Candcnc MTA 100 has at least 12mA of current sinking capability. Or what the number is?

Thanks
Hager

[dan_the_welder]

Mr. Chips,

Look at the opto on your board and look up the manufacturer's data sheet.

The info you seek is there.

Dan

[Mr.Chips]

I circled the componet in the photo, it is labeled "78C232K-HCT541"

I found this information for the HCT541 (TI) But i do not see a "current sinking" Hmmmmm What to do??? Am I looking in the right place? I am electronic challanged, LOL

Thanks
Hager

Photo of board below.

Product Information
Features

’HC540, CD74HCT540 . . . . . . Inverting
’HC541, ’HCT541. . . . . . . . .Non-Inverting
Buffered Inputs
Three-State Outputs
Bus Line Driving Capability
Typical Propagation Delay = 9ns at VCC = 5V, CL = 15pF, TA = 25°C
Fanout (Over Temperature Range)
Standard Outputs. . . . . . . . . . . . . . . 10 LSTTL Loads
Bus Driver Outputs . . . . . . . . . . . . . 15 LSTTL Loads
Wide Operating Temperature Range . . . –55°C to 125°C
Balanced Propagation Delay and Transition Times
Significant Power Reduction Compared to LSTTL Logic ICs
HC Types
2V to 6V Operation
High Noise Immunity: NIL = 30%, NIH = 30% of VCC at VCC = 5V
HCT Types
4.5V to 5.5V Operation
Direct LSTTL Input Logic Compatibility, VIL = 0.8V (Max), VIH = 2V (Min)
CMOS Input Compatibility, Il ≤ 1µA at VOL, VOH

[dan_the_welder]

Hi,

So that chip is not an opto isolator. It is a line driver buffer which helps to maintain clean signals over longer cable runs.

The actual optos are on the UBOB.

I am at the edge of my skill/understanding on this, but I believe that the line driver buffer chip will "insulate" the opto from current overload and should be robust enough for your application.

But I am just guessing now!

I use a Mini-IO and all I had to do was look up the current dissipation of the opto chip and compare it to the needs of the drivers.

Their design architecture has changed with the UBOB and MTA100

[Mr.Chips]

OK I found them on the UBOB, here is the spec sheet "http://media.digikey.com/pdf/Data%20Sheets/Lite-On%20PDFs/LTV-8x6.pdf" still did not see a "current sinking". Would it be called another term?

The id is: LTV846

Thanks
Hager

[Mr.Chips]

Thank you all for your help and suggestions.

I called Candcnc and asked them what was the "current sinking capability" and they said it is 50 ma. And they said that the Gecko 251 only requires 2-3 ma.

So the idea of running two Gecho 251's off of one MTA 100 output is fine, there is a large safety margin.

I am pretty gun shy after smoking three Xylotes driver cards, which was totally my fault for not understanding the proper way to connect them up.

SO the diagram shown below is correct and safe to do because it is hooked up in parallel.

Thanks

Hager