PIC17C752 MICROCHIP [Microchip Technology], PIC17C752 Datasheet - Page 28

• Manufacturer Part Number: PIC17C752
• Description: High-Performance 8-Bit CMOS EPROM Microcontrollers
• Manufacturer: MICROCHIP [Microchip Technology]

FIGURE 5-10: BROWN-OUT SITUATIONS
5.1.5
PIC17C75X devices have an on-chip Brown-out Reset
circuitry. This circuitry places the device into a reset
when the device voltage falls below a trip point (BV
This ensures that the device does not continue pro-
gram execution outside the valid operation range of the
device. Brown-out resets are typically used in AC line
applications or large battery applications where large
loads may be switched in (such as automotive).
A configuration bit, BODEN, can disable (if clear/pro-
grammed) or enable (if set) the Brown-out Reset cir-
cuitry. If V
parameter D005 in electrical specification section), for
greater than parameter D035, the brown-out situation
will reset the chip. A reset is not guaranteed to occur if
V
The chip will remain in Brown-out Reset until V
above BV
and will keep the chip in reset an additional 96 ms. If
V
running, the chip will go back into a Brown-out Reset
and the Power-up Timer will be initialized. Once V
rises above BV
96 ms time delay. Figure 5-10 shows typical Brown-out
situations.
In some applications the Brown-out reset trip point of
the device may not be at the desired level. Figure 5-8
and Figure 5-9 are two examples of external circuitry
that may be implemented. Each needs to be evaluated
to determine if they match the requirements of the
application.
DS30264A-page 28
DD
DD
Note:
falls below BV
drops below BV
BROWN-OUT RESET (BOR)
DD
Before using the on-chip brown-out for a
voltage
review the electrical specifications to
ensure that they meet your requirements.
DD
. The Power-up Timer will now be invoked
Internal
Internal
Internal
DD
Reset
Reset
Reset
falls below BV
V
V
V
, the Power-up Timer will execute a
DD
DD
DD
DD
supervisory
DD
for less than parameter D035.
while the Power-up Timer is
DD
function,
(Typically 4.0V,
DD
please
rises
DD
Preliminary
DD
).
< 96 ms
96 ms
FIGURE 5-8:
FIGURE 5-9:
96 ms
96 ms
This brown-out circuit is less expensive, albeit less
accurate. Transistor Q1 turns off when V
certain level such that:
This circuit will activate reset when V
(Vz + 0.7V) where Vz = Zener voltage.
33k
R1
R2
V
V
DD
DD
V
DD
EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 1
EXTERNAL BROWN-OUT
PROTECTION CIRCUIT 2
10k
•
40 k
40 k
R1 + R2
1997 Microchip Technology Inc.
R1
BV
BV
BV
BV
BV
BV
Q1
DD
DD
DD
DD
DD
DD
Max.
Min.
Max.
Min.
Max.
Min.
MCLR
= 0.7V
V
MCLR
V
PIC17CXXX
PIC17CXXX
DD
DD
DD
goes below
DD
is below a