Maia 發表於 January 22, 2021
When the voltage of the built-in low-voltage reset circuit is different from the application specifications, an external triode low-voltage reset circuit can be used
It can provide low voltage reset function and is suitable for strong interference environment.
The low voltage reset function is determined by the voltage division of R1 and R2, or by the voltage of the Zener diode.
When using R1 and R2 to divide the voltage, the low voltage reset point is about (R1+R2)/(2×R1), and the resistance value of R3 must be greater than R2/30.
When using a Zener diode, its low voltage reset point is about VZ+0.5V, R1 is used to set the operating point VZ, and the resistance value of R3 is preferably greater than 100kΩ.
The position of the transistor Q1 on the PCB is very important. Generally, the shortest wiring between the collector (C) and emitter (E) of Q1 and the RES and VDD pins of the MCU is required.
Lance 發表於 January 22, 2021
This can be done, assuming that the resistance of all resistors is 10k,
VDD linearly rises from 0V to 5V within 100ms. Please draw the #RES waveform according to the above drawing.
Seeing the #RES waveform should be able to understand the principle
Ronan 發表於 January 22, 2021
My understanding is that it is mainly used to detect VDD. When VDD is lower than a certain value (how many two resistances are determined), RES outputs a low level and usually a high level. Generally connected with the RESET of the low-voltage reset microcontroller.
