ST STM32F4 Series

DocID026304 Rev 3 15/44
AN4488 Power supplies
43
Figure 8. NRST circuitry timings example
(not to scale, only for STM32F411xx and STM32F446xx)
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.
Example for STM1061N16:
– Voltage regulator 1.8 V +/- 5% mean V
DD
min1.71 V
– Supervisor specified at 1.60 V +/- 2% with an hysteresis of 5% mean
- rising trip max = 1.71 V (1.60 V + 2% + 5%)
- falling trip min = 1.57 V (1.60 V - 2%).
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