
PIC16F627A/628A/648A
DS40044G-page 108
2009 Microchip Technology Inc.
FIGURE 14-11:
EXTERNAL POWER-ON
RESET CIRCUIT (FOR
SLOW VDD POWER-UP)
FIGURE 14-12:
EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 1
FIGURE 14-13:
EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 2
Note
1:
External Power-on Reset circuit is required
only if VDD power-up slope is too slow. The
diode D helps discharge the capacitor
quickly when VDD powers down.
2:
R < 40 k
Ω is recommended to make sure
that voltage drop across R does not violate
the device’s electrical specification.
3:
R1 = 100
Ω to 1 kΩ will limit any current
flowing into MCLR from external capacitor
C in the event of MCLR/VPP pin break-
down due to Electrostatic Discharge (ESD)
or Electrical Overstress (EOS).
C
R1
R
D
VDD
MCLR
PIC16F627A/628A/648A
VDD
Note
1:
This circuit will activate Reset when VDD
goes below (Vz + 0.7V) where Vz = Zener
voltage.
2:
Internal Brown-out Reset circuitry should
be disabled when using this circuit.
VDD
33k
10k
40k
VDD
MCLR
PIC16F627A/628A/648A
x
R1
R1 + R2
= 0.7 V
VDD
R2
40k
VDD
MCLR
PIC16F627A/628A/648A
R1
Q1
Note
1:
This brown-out circuit is less expensive,
albeit less accurate. Transistor Q1 turns off
when VDD is below a certain level such that:
2:
Internal Brown-out Reset should be
disabled when using this circuit.
3:
Resistors should be adjusted for the
characteristics of the transistor.
VDD x
R1
R1 + R2
= 0.7 V