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STM32F401VDT6 microcontroller :- PWM channel misbehaves after ESD (Electro Static Discharge) testing


We have custom board, having STM32F401VDT6 microcontroller on it. We interfaced a tricolor LED to the Timer 1 PWM channels (CH1- Red, CH2-Green, CH3-Blue). Recently we have ESD test, after that when we stop channel 2 PWM and started CH3 PWM that time CH2's pin is continuously high. But when CH2 PWM is started then this pin behaves as expected (High-Low).

  1. What can be the reason for PWM channel to Pin High, even CH2 PWM is stopped?
  2. Is their any interlinks between the channels ?
  3. Does ESD affects the PWM peripheral of microcontroller?
Chief II

ESD affects everything it hits in a largely unpredictable ways...


> CH2's pin is continuously high

  1. Are you sure this is incorrect behavior? Show the TIM registers.
  2. Everything is linked to some degree.
  3. Of course, potentially.
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> when we stop channel 2 PWM and started CH3 PWM that time CH2's pin is continuously high

What is "stop channel 2 PWM" in terms of TIM (and perhaps GPIO) registers? Why is this behaviour unexpected?

If "stop channel 2 PWM" means effectively threestating the pin, ESD testing might've opened some leak path to VDD, e.g. shorted the transistor which switches on the internal pullup. There's probably also a higher current consumption when the pin is driven (PWM is on), but the difference may be low, depending on circumstances.


In general, when PWM section is broken due to ESD damage, how is it broken? (Short circuit or open circuit or continuous high etc.)