+5V, Low-Power µP Supervisory Circuits
with Adjustable Reset/Watchdog
______________________________________________________________Pin Description
PIN
NAME
RESET IN
GND
SRT
FUNCTION
Reset Input. High-impedance input to the reset comparator. Connect this pin to the center point of an
external resistor voltage-divider network to set the reset threshold voltage. The reset threshold voltage
is calculated as follows: V
RST
= 1.22 x (R1 + R2) / R2 (see
Typical Operating Circuit).
Ground
Set Reset-Timeout Input. Connect a capacitor between this input and ground to select the reset timeout
period (t
RS
). Determine the period as follows: t
RP
= 2.67 x C
SRT
, with C
SRT
in pF and t
RP
in µs (see
Typical Operating Circuit).
Set Watchdog-Timeout Input. Connect a capacitor between this input and ground to select the basic
watchdog timeout period (t
WD
). Determine the period as follows: t
WD
= 2.67 x C
SWT
, with C
SWT
in pF
and t
WD
in µs. The watchdog function can be disabled by connecting this pin to ground.
Watchdog-Select Input. This input selects the watchdog mode. Connect to ground to select normal mode
and the basic watchdog timeout period. Connect to V
CC
to select extended mode, multiplying the basic
timeout period by a factor of 500. A change in the state of this pin resets the watchdog timer to zero.
Watchdog Input. A rising or falling transition must occur on this input within the selected watchdog
timeout period, or a reset pulse will occur. The capacitor value selected for SWT and the state of WDS
determine the watchdog timeout period. The watchdog timer clears and restarts when a transition
occurs on WDI or WDS. The watchdog timer is cleared when reset is asserted and restarted after reset
deasserts. In the extended watchdog mode (WDS = V
CC
), the watchdog function can be disabled by
driving WDI with a three-stated driver or by leaving WDI unconnected.
Open-Drain, Active-Low Reset
Output (MAX6301)
Push/Pull, Active-Low Reset
Output (MAX6303)
Open-Drain, Active-High Reset
Output (MAX6302)
Push/Pull, Active-High Reset
Output (MAX6304)
Supply Voltage
RESET
changes from high to low whenever the monitored voltage
(V
IN
) drops below the selected reset threshold (V
RST
).
RESET
remains low as long as V
IN
is below V
RST
. Once V
IN
exceeds V
RST
,
RESET
remains low for the reset timeout period and then goes high.
The watchdog timer triggers a reset pulse (t
RP
) whenever the watch-
dog timeout period (t
WD
) is exceeded.
RESET changes from low to high whenever the monitored voltage
(V
IN
) drops below the selected reset threshold (V
RST
). RESET
remains high as long as V
IN
is below V
RST
. Once V
IN
exceeds V
RST
,
RESET remains high for the reset timeout period and then goes low.
The watchdog timer triggers a reset pulse (t
RP
) whenever the watch-
dog timeout period (t
WD
) is exceeded.
MAX6301–MAX6304
1
2
3
4
SWT
5
WDS
6
WDI
RESET
(MAX6301/3)
7
RESET
(MAX6302/4)
8
V
CC
_______________________________________________________________________________________
5
MAXIM [ MAXIM INTEGRATED PRODUCTS ]
