Datasheet

PIC16F627A/628A/648A
DS40044G-page 108 © 2009 Microchip Technology Inc.
FIGURE 14-11: EXTERNAL POWER-ON
RESET CIRCUIT (FOR
SLOW V
DD 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 V
DD power-up slope is too slow. The
diode D helps discharge the capacitor
quickly when V
DD powers down.
2: R < 40 kΩ is recommended to make sure
that voltage drop across R does not violate
the device’s electrical specification.
3: R1 = 100Ω 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
V
DD
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
V
DD
MCLR
PIC16F627A/628A/648A
x
R1
R1 + R2
= 0.7 V
VDD
R2
40k
V
DD
MCLR
PIC16F627A/628A/648A
R1
Q1
Note 1: This brown-out circuit is less expensive,
albeit less accurate. Transistor Q1 turns off
when V
DD 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