MAX821 Maxim, MAX821 Datasheet - Page 6

• Manufacturer Part Number: MAX821
• Description: 4-Pin P Voltage Monitors with Pin-Selectable Power-On Reset Timeout Delay
• Manufacturer: Maxim

When V
no longer sinks current—it becomes an open circuit.
Therefore, high-impedance CMOS logic inputs con-
nected to the RESET output can drift to undetermined
voltages. This presents no problem in most applica-
tions, since most P and other circuitry is inoperative
with V
RESET output must be valid down to 0V, adding a pull-
down resistor to the RESET pin will cause any stray
leakage currents to flow to ground, holding RESET low
(Figure 2a). R1’s value is not critical; 100k
enough not to load RESET, and small enough to pull
RESET to ground.
A 100k
for the MAX822 if RESET is required to remain valid for
V
µPs with bidirectional reset pins (such as the Motorola
68HC11 series) can contend with the MAX821 reset
output. For example, if the MAX821 RESET output is
asserted high and the µP wants to pull it low, indetermi-
nate logic levels may result. To correct such cases,
connect a 4.7k
output and the µP reset I/O (Figure 3). Buffer the reset
output to other system components.
TRANSISTOR COUNT: 492
4-Pin µP Voltage Monitors with Pin-Selectable
Power-On Reset Timeout Delay
6
___________________Chip Information
CC
_______________________________________________________________________________________
< 1V (Figure 2b).
CC
CC
below 1V. However, in applications where the
pull-up resistor to V
falls below 1V, the MAX821 RESET output
Ensuring a Valid RESET Output
resistor between the MAX821 RESET
Bidirectional Reset Pins
Interfacing to µPs with
CC
Down to V
is also recommended
CC
is large
= 0V
Figure 2. RESET/ RESET Valid to V
Figure 3. Interfacing to µPs with Bidirectional Reset I/O
a)
MAX821
GND
V
CC
MAX821
RESET
GND
V
V
CC
CC
RESET
4.7k
R1
RESET
CC
BUFFER
GND
b)
V
CC
P
= Ground Circuit
MAX822
GND
V
V
CC
CC
BUFFERED RESET
TO OTHER SYSTEM
COMPONENTS
RESET
R1