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Hysteresis in analog watchdog STM32L052 operation when monitoring value are changed near thresholds.

ViktorD
Associate

Hi, everyone.

I had used analog watchdog in STM32L052 MCU to monitor supply voltage of device for determinate when it's value will be less then low threshold level (LT in ADC_TR). High threshold I tunned to maximum value (4095).If voltage is between thresholds and more than low threshold the analog watchdog isn't triggering interrupt as intended. But interesting behavior is observed when supply voltage is changed near low threshold. If voltage changed from maximum level to minimum and when its value are crossing down low threshold - analog watchdog interrupt is executed. Then I increase supply voltage and watch ADC data when analog watchdog interrupt is executing. In this mode I notised - interrupt from analog watchdog (AWD) is executing when ADC data value are little more than low threshold. For example, low threshold value is 2477. From maximum to minimum voltage change is triggered AWD interrupt at value 2472. Then ADC data value became 2524 - AWD interrupt is triggered. It's ceases when ADC value became more or equal 2608. If then change it to 2504 - AWD interrupt not triggered while it's not crossing down low threshold. It's phenomena of work called hysteresis and for this case it value is 130 (in scale data values ADC).

It's normal operational of analog watchdog (in reference manual it's behavior are not described)? Who observed similar behavior of analog watchdog STM32 MCU?

Thanks for all answers.

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