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Damaged? 2.5V at PA4 in Reset state (STM32F446VET)

Question asked by Miro Mico on Jun 29, 2017
Latest reply on Jun 29, 2017 by waclawek.jan


Im trying to optimize LowPower current consumption of a custom board my hardware guys have made arround a 100pin LQFP STM32F446VET. Currently I fight to find the source of a faulty voltage at GPIO PA4 (Pin 29 with this housing). I desoldered the pin from the board that it is not connected to anything. The pin outputs a voltage of 2.5V after reset and in GPIO's reset state. When I configure the pin as a normal GPIO I can output a 0 (0 Volts). But as soon as I call HALs HAL_GPIO_DeInit() the 2.5 Volt output re-appears. When I measure the current from this 2.5 Volts to ground I see 240µA on my ampmeter. This is the equivalent of a 10 kOhm impendance. According to the datasheet this pin has alternate functions like DAC_OUT1 and USB_OTG_HS_SOF. But all GPIOx->AFR[] are set to 0. Same behavior on a second identical board.

Is it possible that I damaged the pin by a connected 8 Ohm @ 1 kHz loudspeaker (induced reverse or high voltage by the speakers high inductance)?

Any idea, what is going wrong with my device?