AN4488 Rev 7 15/50
AN4488 Reset and power supply supervisor
49
Figure 6. NRST circuitry timings example (not to scale, only for STM32F410xx,
STM32F411xx, STM32F412xx, STM32F413xx, STM32F423xx, STM32F446xx,
STM32F469xx and STM32F479xx)
Selection of NRST voltage supervisor
Voltage supervisor should have the following characteristics
• Reset output active-low open-drain (output driving low when voltage is below trip
point).
– Supervisor trip point including tolerances and hysteresis should fit the expected
V
DD
range.
Notice that supervisor spec usually specify trip point for falling supply, so
hysteresis should be added to check the power on phase.
3.2 Power supply supervisor
3.2.1 PDR_ON circuitry example
Note: This example doesn’t apply to STM32F410xx, STM32F411xx, STM32F412xx,
STM32F413xx, STM32F423xx, STM32F446xx, STM32F469xx and STM32F479xx, where
PDR_ON can be connected to VSS to permanently disable internal reset circuitry (external
voltage supervisor required on NRST pin). Thanks to backward compatibility, circuitry built
for other STM32F4xxxx products will work for STM32F410xx, STM32F411xx,
STM32F412xx, STM32F413xx, STM32F423xx, STM32F446xx, STM32F469xx and
STM32F479xx.
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