SN8F2250B Series
USB 2.0 Full-Speed 8-Bit Micro-Controller
3.6.2 Diode & RC Reset Circuit
VDD
R1
47K ohm
DIODE
R2
RST
VSS
MCU
100 ohm
C1
0.1uF
VCC
GND
This is the better reset circuit. The R1 and C1 circuit operation is like the simply reset circuit to make a power on signal.
The reset circuit has a simply protection against unusual power. The diode offers a power positive path to conduct
higher power to VDD. It is can make reset pin voltage level to synchronize with VDD voltage. The structure can
improve slight brown out reset condition.
Note: The R2 100 ohm resistor of “Simply reset circuit” and “Diode & RC reset circuit” is necessary to
limit any current flowing into reset pin from external capacitor C in the event of reset pin
breakdown due to Electrostatic Discharge (ESD) or Electrical Over-stress (EOS).
3.6.3 Zener Diode Reset Circuit
VDD
R1
33K ohm
E
C
R2
10K ohm
B
Q1
RST
MCU
Vz
R3
40K ohm
VSS
VCC
GND
The zener diode reset circuit is a simple low voltage detector and can improve brown out reset condition
completely. Use zener voltage to be the active level. When VDD voltage level is above “Vz + 0.7V”, the C terminal of
the PNP transistor outputs high voltage and MCU operates normally. When VDD is below “Vz + 0.7V”, the C terminal of
the PNP transistor outputs low voltage and MCU is in reset mode. Decide the reset detect voltage by zener
specification. Select the right zener voltage to conform the application.
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