MAX809 ON, MAX809 Datasheet - Page 4

• Manufacturer Part Number: MAX809
• Description: 3-Pin Microprocessor Reset Monitors
• Manufacturer: ON

V CC Transient Rejection
reset timing during power–up, power–down, and
brownout/sag conditions, and rejects negative–going
transients (glitches) on the power supply line. Figure 1
shows the maximum transient duration vs. maximum
negative excursion (overdrive) for glitch rejection. Any
combination of duration and overdrive which lies under the
curve will not generate a reset signal. Combinations above
the curve are detected as a brownout or power–down.
Transient immunity can be improved by adding a capacitor
in close proximity to the V
RESET Signal Integrity During Power–Down
Below this voltage the output becomes an ”open circuit” and
does not sink current. This means CMOS logic inputs to the
systems are completely shutdown well above this voltage.
However, in situations where RESET must be maintained
valid to V
from RESET to ground to discharge stray capacitances and
Figure 1. Maximum Transient Duration vs. Overdrive
P will be floating at an undetermined voltage. Most digital
The MAX809/810 provides accurate V
The MAX809 RESET output is valid to V
400
320
240
160
CC
90
0
V CC
1
= 0V, a pull–down resistor must be connected
RESET COMPARATOR OVERDRIVE,
for Glitch Rejection at 25 C
T A = +25 C
MAX8xxR/S/T
10
(V TH – V CC (mV)
MAX8xxL/M/J
Duration
CC
pin of the MAX809/810.
100
Overdrive
V TH
CC
APPLICATIONS INFORMATION
monitoring and
1000
CC
MAX809, MAX810
= 1.0V.
http://onsemi.com
4
hold the output low (Figure 2). This resistor value, though
not critical, should be chosen such that it does not
appreciably load RESET under normal operation (100k
will be suitable for most applications). Similarly, a pull–up
resistor to V
high RESET for V
Processors With Bidirectional I/O Pins
bi–directional reset pins. Depending on the current drive
capability of the processor pin, an indeterminate logic level
may result if there is a logic conflict. This can be avoided
by adding a 4.7k
MAX809/810 (Figure 3). If there are other components in
the system which require a reset signal, they should be
buffered so as not to load the reset line. If the other
components are required to follow the reset I/O of the P, the
buffer should be connected as shown with the solid line.
Some
V CC
Figure 3. Interfacing to Bidirectional Reset I/O
Figure 2. Ensuring RESET Valid to V CC = 0 V
MAX809
V CC
GND
RESET
CC
P’s (such as Motorola 68HC11) have
is required for the MAX810 to ensure a valid
W
CC
MAX809
resistor in series with the output of the
47 k
V CC
V CC
GND
below 1.0V.
RESET
RESET
BUFFER
GND
V CC
m
P
BUFFERED RESET
TO OTHER SYSTEM
COMPONENTS
R1
100 k
W