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Problems with ADC and PWM in Kinetis KE06Z

Question asked by Leonardo Moreno on Aug 29, 2016
Latest reply on Aug 30, 2016 by Leonardo Moreno

Hi, I'm introducing myself to the Kinetis family and so far it has proven to be great por my application.


Just as a note, I don't have a Deep knowledge around the operating fundamentals of this kind of boards. So still working with interrupts and timer units is a bit confusing.


However, I'm currently having a problem while Reading temperature through the ADC while having an PWM output in other pins.


So what I'm doing is Reading the temperatura of 2 external thermistors through the ADC. With that I haven't had any problem and also the signal has almost no noise (after being filtered with an RC circuit and using an OPAMP).


I'm Reading the temperature continously using the Measure(TRUE) and GetValue() methods.


At the same time I'm controlling an external IBT-2 H-Bridge using two pins with PWM (both pins share the same Timer Unit).


I'm not having any problems in the signal when I have a duty cycle in any of the PWM's of zero or full (0 or 65535 with function SetRatio16() ). However when I send a signal of 20,000, 30,000, 40,000 or anything near this values, the ADC signal turns incredibly noisy.


The H-Bridge is controlling a Peltier Cell at 14 V and máximum current demand of about 5 Amps (It's rated for Max 26 V and 43 Amps and PWM of 25 KHz)


My pwm period is 750 us so that's around 1 KHz.


It has to do with the H-bridge, since if I send a PWM of any value while reading the temperature while disconnecting the external power source that feeds the Peltier Cell, no noise arises.


I've been battling with this for some time now.


Has anyone have had this kind of problem?


Thank you.