I've designed the DRV103 in a circuit like the aplication Circuit Figure 16. Remotely Opreated Solenoid Valve or Relay,in the datasheet DRV103 (SBVS029A-June 2001).Also the recommended 100pF capacitor parallel with Rpwm is used. The oscillator frequency is is adjust by a 200k resistor (Rfreq),and the duty cycle is adjust with a 133k resistor (Rpwm).
Now I have problems with the EMI, and espacially with the electromagnetic field immunity test for EN61000-4-3.It seems that the frequency and the duty cycle is not stable.
Please let me know if the problem is known, and what can I do to get rid of this fault.
Many thanks for your efforts.
I'm sorry you are having difficulty using the DRV103. I have some questions to help diagnose the situation:
Have looked at waveforms with an oscilloscope? Does the basic frequency look stable on the oscilloscope? You refer to unstable frequency and duty cycle. Can you quantify what you are experiencing? Do you see an unstable waveform as shown in the top of figure 6?
RF interference can be caused by layout issues. Connections to the load should be made with twisted pair. The +Vs side of the twisted pair should be connected close the the DRV103 and its bypass capacitor. It is often better to locate the flyback diode close to the DRV103, not at the solenoid. The selection of the flyback diode can make a difference in RFI. Some slower diode types can create RF noise as they turn off. A fast-recovery type should be used.
thanks for your help. in the PDF Screenshots you can see the waveform in differnt situations.
Figure 1: This is the waveform with no disturbance.
Figure 2-5 shows the waveform, when the conducted disturbance is activated.in this case the circuit is acted with the conducted disturbance of 5V(80%AM(1kHz)) at the 24V supply-line .The frequenz where the fault appear's, is between 100MHz-300MHz.The disturbance is coupled by a injection Clamp to the 24V supply-line.
We choose the test of conducted disturbance by EN61000-4-6 for the pre compliance test for the electromagnetic field immunity test by EN61000-4-3.We must test with 10V/m by EN61000-4-6. this should be equal 8-10V by conducted disturbance withthe injection clamp, because we have seen, that the disturbance is coupled by the lines to the unit.
The only way I found to protect the DRV103 against this disturbance is a extern Filter in the 24V supply line, but this is not practicabe.Do you know a protective circuit at the DRV103 which solve the Problem too?
I think the problem is not causes by the flyback diode, because we have the same problems, when we have a normal resistor as load.
Thanks for the additional information. I'm not surprised that 5V of 100MHz to 300MHz on the supply voltage of the DRV103 causes problems with its operation. This level of high frequency voltage would be very disruptive to internal circuitry.
You are assuming that the radiated RF field has a fixed relationship to the conducted level on the 24V power line. I think the solution must be to change this expected relationship. This could come from a various measures:
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