Option to disable MC4x DOUT Open Load detect

J C. Crow 4 years ago in IQANdesign updated by Gustav Widén (System support) 1 year ago 9

I am using several DOUT channels on and MC43 and XC44 to drive LED lights. When we crank the engine or run the electric hydraulic pump, I get open load errors on these channels.  I already have undercurrent detection turned off on these outputs.  I am using IQAN Design This is a 12 V system. The LED light is a Grote BZ101-5, 16 W total power.  The channels are set up as a Digital Out HS. The pins used are MC43 C1-46, C1-48 and XC44 C2:49 and C2-50.

I have installed a 120 ohm pull down resistor in parallel with these lights to prevent the error.  This is a costly and undesirable way to fix this issue.  I am requesting an that the open load detection be software configurable to prevent these errors from occurring. 

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With the undercurrent detection disabled, it must be the off-state open load detection that trigger the open load detection.

But then a 120 ohm resistor seems way to low. That will pull enough current to exceed the on state undercurrent detection threshold. 

To add a load that effectively disables the off-state open load detection, resistor value as high as 17 kOhm should be fine, reducing unnecessary power loss. 

See Digital out HS Diagnostic info in Appendix A: 

IQAN-MC4x instruction book Appendix A

Still, an external resistor adds unnecessary wiring. If you want to I can change the topic to a feature request for a disabling option? 

(a feature for disabling open load would't eliminate the 2 mA leakage that comes as an effect of the off-state open load detect, but that leakage is more of an issue for smaller LED:s) 

The fault only occurs with the output in the off condition. I am not sure what it is with these LED lights that the module sees these as an open load when cranking. The 120 ohm resistor was selected because they are readily available in a ruggedized form. Deutsch connectors are available with 120 ohm resistors built in. The leakage current at 12 V is about 100 mA, which is not insignificant, but does not exceed the power rating of the resistor or the output. I almost had this fixed with a software tweek by disabling the outputs when cranking the auxiliary engine. Unfortunately, I still get the error when cranking the chassis engine. I don't have visibility of the chassis engine cranking condition, so I can't disable the lights when this occurs.  I even tried disabling the output after the open load fault occurs, but the on screen message does not go away.

I would much rather not have to install these resistors. If you can change this to a feature request, that would be great. That's really what I was hoping for as the ideal solution. 

Ok, I see. 

I edited the title and changed topic to feature request.


Could it not help to disable the function group when LED is off or voltage is <12V?


I tested disabling the output based on system voltage and that seems to have resolved the issue. Thank you for the suggestion. 


Would it eventully be possible to disable those error on PWM output as well !&!? We just need a PWM signal and get a lot of trouble with an 1kohm resistor. Sounds like we are forced to put inductive load or really low impedance load to avoid some critical error ! 


PWM out HS will get this option too, but not PWM out HS+LS (as discussed in this post about PWM out HS+LS). 

That is great news Gustav.

While we are on the topic of load detection, would it be possible via a status channel to see the approximate current or voltage on a PWM output?

This would be very helpful when driving small motors and valves detect what is happening.

A property to disable reporting of open load detect was was added in IQANdesign 6.07, see Release notes - IQANdesign 6 

Property to disable C4x DOUT/PWM out HS open load detection

Note that this does not change the leakage current on outputs.