Kevin Kramb

PWM kills RTC oscillator

Discussion created by Kevin Kramb on Apr 19, 2012
Latest reply on May 10, 2012 by FridgeFreezer

I have a custom MCF52258 board design.  It has an oscillator circuit with a 32.768 KHz crystal that drives the internal RTC.  The oscillator and the RTC work normally until I turn on a particular PWM output. When the PWM output is enabled the oscillator circuit stops oscillating and therefore the RTC stops counting seconds.  The PWM is operating in the range of 5 - 50 KHz with a 50% duty cycle.  This problem occurs with PWM2 and does not occur with PWM4 or PWM6.  The microcontroller is the 144 pin LQFP.  On this package PWM2 (pin 12) is right next to the RTC_EXTAL pin (13).

 

Do you have any suggestions for how to fix this problem?  Right now my best idea is to revise the board to use a different PWM channel. :smileysad:

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