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Safety COUTs as DOUTs

Kevin 3 weeks ago in Master modules / MC4x updated by Gustav Widén (System support) 2 weeks ago 1

We have a project that requires control of multiple cylinders, each cylinder is connected to a double acting valve, 2 separate coils, one for each cylinder movement (in/out). These outputs must be safety in our application.

Reading the instruction manual for the DOUTs on MC43FS, it states we must use only one DOUT HS and one DOUT LS per output when its being used in a safety application, so the controller can switch the valve off by either side in event of a fault. Therefore I have concluded we can only have 5 DOUT safety per MC43FS. Or in other words, 2.5 cylinder valve controls.

Can I instead use COUT, and therefore each cylinder function can be driven by a complete COUT A? For example, i can technically connect 10 cylinders, in/out, i.e. 20 valves? I would have to ensure the current does not exceed the limitations of the groups, but does having the shared COUT + affect the safety aspect of a COUT? There is a note saying all COUTs are safety, and nothing about sharing pins like there is under DOUT so I guess I can overcome my issue of limited DOUTs for safety?


I guess if there was a function other than driving a component in a direction it would not be possible, as you can only drive a COUT in either + or - direction, i.e. not both if you has different valves to energise, which could be at the same time.


Also it explicitly states no diodes on a coil connected to COUT (I guess for regulation), does this still apply if I'm using COUTs digitally, ramping from 0-100% and 100-0%? Would the collapsing digital coil cause damage to the COUT driver?

A bidirectional COUT can be used for driving a pair of coils on an on-off directional valve. 


One thing you need to think of is setting the commanded current to a level that is physically possible to drive. 

(not the datasheet value on coil current, those numbers are usually at room temperature). If you set commanded current too high, you will be seeing saturation warnings and open load if it is way too high. 


As for diodes, the IQAN COUT has an internal diode in the circuit that handles the switching transient for the PWM. You are right that the main reason for recommending against an external diode on a COUT is that the external diode messes with the current regulation. You won't damage the COUT with an external diode. 

But do consider the stopping performance on the function.