DOUT LS issue with LED

Brendon 1 year ago in Master modules / MC4x updated by Chris Litwin 1 year ago 3


I have 4 LEDs each connected to a DOUT LS channel on an MC43.

The issue I have is they each turn on faintly even when the output is off.

Once the DOUT is on the light appears brighter.

The LEDS themselves are 12V LEDs like this one (though each is a different color):


I don't currently have a Current Limiting Resistor inline, would not having that cause this sort of behavior?

Or is there something else I am missing about operating LEDs off the DOUT channels?

The MC43 Digital out LS (Low side) have a leakage current. 

In the instruction book Appendix A, it just says < 200 uA. 

Image 3686

On the MC4x/XC4x Digital out LS, you can actually avoid this leakage by disabling DOUT output load detection. 

You find the prorperty to control this on the pin in the block diagram in IQANdesign. 

Image 3685


Are you able to stop the leakage current on any of the other outputs on an MC4x, XC4x, or MD4?


Thanks for your reply, and the solution.

I am using these pins:

C2:43 - OUT_39 - DOUT-AC (LS)

C2:63 - OUT_40 - DOUT-AD (LS)

C2:44 - OUT_41 - DOUT-AE (LS)

C2:64 - OUT_42 - DOUT-AF (LS)

In the MC4x instruction manual I was referencing the following, in the graphic it appears to include a resistor, and then under 'Function' in mentions a current limiting resister.  The info you've provided clears things up. I've disabled the DOUT open load detection.

Image 3687