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Overload Errors when PWMOuts are Off

8 years ago in Master modules / MC3 • updated by 8 years ago • 4

We have just updated from IQAN 3.19 to IQAN 4.06.

We are now seeing over load errors on several solenoids being controlled with PWM out signals.

The overloads only occur when the outputs are off. When they are on (90% Duty cycle) the errors go away.

I believe I remember reading something about circuit failure detection being active even when outputs are off as part of an IQAN 4 update.

Any recommendations on how this could be resolved?

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8 years ago

The output error detection differs between different IQAN modules.

All modules have some protection for overload situations like short to ground on the output, but It is not all modules that have diagnostics reporting of this error, and not all modules have detection in the off state.

IQAN-MC3 is a module that can detect SCG of the highside when the PWM out is off. But it has had this since the module was introduced in 2.50, and there is very little reason to use an MC3 output as open PWM instead of COUT.

What type of module is this happening on? The IQAN-XC10? It has PWM outputs with various diagnostic reporting of faults when the output is on, but should not be reporting this when the module is off.

One possibility is that the overload occurred when the output was on. The output remains in the error status until it has had a zero command and then gets activated again.

But this does not really match the symptom you are describing, that you had to get to 90% duty cycle before the error went away.

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8 years ago

thank you for the quick response.

We are using an MC3 module in fact. I am not sure why we are using PWM instead of Cout but we made this change a while ago.

We tracked the issue down to some faulty circuitry in a passive junction board, so problem is resolved now.

It definitely only happened when the function was off and went away when the function was on... I still find this curious but the problem is resolved now so no worries.

thanks again!

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8 years ago

Good to hear that you already solved it, and thank you, the information that the module with the PWM out channel was an IQAN-MC3, that explains it to me.

What believe happened is that you had the PWMRET pins shorted to ground.

The method used for detecting faults on IQAN-MC3 outputs when the outputs channels are off but enabled is that the high-side switch is on, while the low side is off. This is the way it has worked from the start in version 2.50.

With IQAN-MC3 COUT, when the output is off, a CRET SCG leads to an activation of the coil for <100 ms, and then shutdown of the output using both highside and lowside.

With IQAN-MC3 COUT, when the CRET SCG occurs with the output is already on, this leads to an increase in current for <100 ms, and then shutdown of the output using both highside and lowside.

See the IQAN-MC3 manul appendix B for details on COUT (and DOUT) failure modes.

Reactivation is restricted by the COUT restart behavior.

For the open PWM configuration, there is no such list, only the much more limited Appendix A information about diagnostics in different modes.

On an IQAN-MC3 PWM out, the current measurement is not used. Because of this, the error detection is not complete, and this is the main reason for not allowing the open control PWM in safety functions.

With IQAN-MC3 PWM out, when the output is off, a short to ground on the PWMRET leads to an activation of the coil for <100 ms, and then shutdown of the output via the highside switch.

With IQAN-MC3 PWM out, when the output is on, a short to ground on the PWMRET cause an increase in current, as PWM:ing on the return pin has no effect. Because there is no current measurement in this open control mode, this is not detected.

I think it is very unusual to configure the MC3 proportional outputs as open control PWM instead of COUT. The only reason to do so in an IQAN-MC3 is to avoid some of the COUT error detection, e.g. if there is a need to drive a current below the COUT controllable range.

Please be aware that the open control PWM out channel cannot be used in safety functions. IQANdesign will mark it as an error if you place the PWM out channel in a function group marked as safety related.