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

[ABhan.1]

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?

[Piranha]

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

[TDK]

> 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.

[waclawek.jan]

> 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.

JW

[ABhan.1]

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