Author Topic: Ground with Output Pin  (Read 5606 times)

Offline CShultz

  • PLUS+1 Developer
  • ***
  • Posts: 25
  • Karma: +0/-0
    • TST Hydraulics
Ground with Output Pin
« on: September 06, 2014, 10:28:49 PM »
I was reviewing the Output Configurations document (520L0922) and it discusses some FMEA considerations in regards to bringing the ground back into the micro controller through an output pin, instead of grounding the load externally.  Does not mention any particular instruction/requirement for configuring an output pin as a ground pin.  Say I was running a uni-directional PWM coil, could I bring my ground back into an output?  Would I have to choose a particular pinconfig (sinking?)

Offline Marbek_Elektronik

  • PLUS+1 Guru
  • *****
  • Posts: 315
  • Karma: +7/-0
    • Marbek Elektronik
Re: Ground with Output Pin
« Reply #1 on: September 07, 2014, 09:03:13 AM »
Please connect the ground of controller and ground of coil as near as possible to the controller: create a star point.
so if the ground is loss, the output also have no ground.

It is better for EMV to make no current loops:
The current flows from the controller to the coil and comes BACK to the controller.
Do not connect the ground of the coil  to the ground of the machine near the coil.
Please go with this ground back to the star point , near the controller.
Marbek Elektronik, Dipl.-Ing. Bernd Konrad
Dienstleistung, Entwicklung, Herstellung

Offline CShultz

  • PLUS+1 Developer
  • ***
  • Posts: 25
  • Karma: +0/-0
    • TST Hydraulics
Re: Ground with Output Pin
« Reply #2 on: September 07, 2014, 12:23:24 PM »
Thank you for your prompt reply.  That does not really answer my question however.  According to the documentation I provide in my example,  it says you can connect the ground of a load to an unused output pin.  This way,  if your controller loses ground, so does the load and it creates an open circuit.  I understand this will absorb/use an output pin, but if I have some extra outputs.. Can I use them to return the negative side of the load back to the controller.  I understand grounding near the controller is almost the same thing.. However, say the ground pin was ripped out from the Deutsch connector.. Your load would still have a path to ground if grounded externally.  No matter how close to the controller you are.  I'm asking about the capability of the MC.. Not necessarily what is common practice.  Based on the literature,  it sounds like it is almost recommend to do this for critical functions.  I appreciate your input on the matter.

Offline Jakob

  • PLUS+1 Expert
  • ****
  • Posts: 95
  • Karma: +2/-0
Re: Ground with Output Pin
« Reply #3 on: September 08, 2014, 08:48:02 AM »
Yes you can.
On the multifunctional outputs you can use the pinconfig, and set it to 2 = Digital Output, Sinking Output.
Otherwise you can also use the push/pull setup (0 = Digital Output, Push/Pull Output).

But I would recommend going with the star point ground connection as close as possible to the controller, that Marbek mentioned.
Because drawing too much current through the controller ground might cause a few issues.

I only use the push/pull setup for controlling an electric actuator, which needs to move both ways.

Offline BRIan

  • PLUS+1 Expert
  • ****
  • Posts: 51
  • Karma: +2/-0
Re: Ground with Output Pin
« Reply #4 on: September 09, 2014, 05:35:28 AM »
Jakob, Do you mean like a H bridge? Config = 7

Offline CShultz

  • PLUS+1 Developer
  • ***
  • Posts: 25
  • Karma: +0/-0
    • TST Hydraulics
Re: Ground with Output Pin
« Reply #5 on: September 09, 2014, 05:51:56 AM »
I was thinking something similar to an H bridge but as I am not familiar with them I didn't want to confuse myself/make matters worse.  I am working on a propel application so the more I can protect unintentional movement the better.


Offline FluidPowerTom

  • PLUS+1 Guru
  • *****
  • Posts: 265
  • Karma: +20/-0
Re: Ground with Output Pin
« Reply #6 on: September 10, 2014, 06:42:03 PM »
I think you only want to select config 7 (HBridge) or config 8 if you're doing bidirectional control (2 coils for extend/retract type function) and want to ground through the controller.  If you're just wanting to ground a single coil (not part of a bidirectional control) through the controller then go with either config Jakob has mentioned there.

That said, whether or not this is better from a FMEA standpoint seems to me to be tenuous or at best system specific.  If you're using good wiring practice and a common ground then wiring your coil ground back through the controller wouldn't seem to matter.  The only benefit I could see is that you only need one cable for your device - from the MC to the coil - instead of also having to go from the coil to your common ground.  Another cable is another potential failure I guess...

« Last Edit: September 10, 2014, 06:47:19 PM by FluidPowerTom »
Mechanical Engineer
Hydra-Power Systems - Distributor - Pacific Northwest

Offline oiltronic

  • PLUS+1 Guru
  • *****
  • Posts: 169
  • Karma: +14/-0
Re: Ground with Output Pin
« Reply #7 on: September 16, 2014, 08:01:09 AM »
Say I was running a uni-directional PWM coil, could I bring my ground back into an output?
Yes, one that allows sinking.
  Would I have to choose a particular pinconfig (sinking?)
Yes, sinking.  The positive coil line would go to a sourcing output and the negative coil line would go to a sinking output.  The sinking output should be left on while the function is active at any PWM level.  You could turn off the sinking output when the function is to be turned completely off.  Be sure to have a flyback diode across the coil.