MAX6822 MAXIM [Maxim Integrated Products], MAX6822 Datasheet - Page 6

• Manufacturer Part Number: MAX6822
• Description: Low-Voltage SOT23 ?P Supervisors with Manual Reset and Watchdog Timer
• Manufacturer: MAXIM [Maxim Integrated Products]

Low-Voltage SOT23 µP Supervisors with
Manual Reset and Watchdog Timer
Figure 1. Functional Diagram
Disable the watchdog function by leaving WDI uncon-
nected or by three-stating the driver connected to WDI.
The watchdog input is internally driven low during the
first 7/8 of the watchdog timeout period and high for the
last 1/8 of the watchdog timeout period. When WDI is left
unconnected, this internal driver clears the 1.6s timer
every 1.4s. When WDI is three-stated or unconnected,
the maximum allowable leakage current is 10µA and the
maximum allowable load capacitance is 200pF.
The MAX6821/MAX6822/MAX6823/MAX6824 WDI inputs
are internally driven through a buffer and series resistor
from the watchdog timer
unconnected, the watchdog timer is serviced within the
watchdog timeout period by a low-high-low pulse from
the counter chain. For minimum watchdog input current
(minimum overall power consumption), leave WDI low for
the majority of the watchdog timeout period, pulsing it
low-high-low once within the first 7/8 of the watchdog
timeout period to reset the watchdog timer. If WDI is
externally driven high for the majority of the timeout peri-
od, up to 160µA can flow into WDI.
6
(MAX6821/MAX6822/MAX6823,
_______________________________________________________________________________________
(MAX6821– MAX6824)
MAX6825)
Applications Information
V
WDI
MR
CC
Watchdog Input Current
(Figure 1). When WDI is left
V
CC
TRANSITION
WATCHDOG
DETECTOR
1.26V
GND
Since the RESET output on the MAX6822 is open drain,
it interfaces easily with µPs that have bidirectional reset
pins, such as the Motorola 68HC11. Connecting the µP
supervisor’s RESET output directly to the microcon-
troller’s RESET pin with a single pullup resistor allows
either device to assert reset (see Figure 4).
These supervisors are relatively immune to short-dura-
tion, negative-going V
usually do not require the entire system to shut down.
Figure 2. Reset Timing Diagram
GENERATOR
WATCHDOG
RESET
TIMER
GND
RESET
RESET
V
1V
CC
MAX6821–
MAX6825
Negative-Going V
V
TH
t
t
RP
RP
CC
Bidirectional Reset Pins
Interfacing to µPs with
transients (glitches), which
RESET (MAX6822
RESET
(MAX6821/MAX6824/ MAX6825)
CC
V
TH
Transients
–
MAX6825)
1V
t
t
RD
RD