Single-/Dual-/Triple-Voltage µP Supervisory
Circuits with Independent Watchdog Output
Pin Description
PIN
NAME
FUNCTION
MAX6730
MAX6731
MAX6732
MAX6733
MAX6734
MAX6735
Active-Low Reset Output. The MAX6730/MAX6732/MAX6734 provide an open-
drain output. The MAX6731/MAX6733/MAX6735 provide a push-pull output. RST
1
2
1
2
1
2
RST asserts low when any of the following conditions occur: V 1 or V 2 drops below
CC CC
its preset threshold, RSTIN drops below its reset threshold, or MR is driven low.
Open-drain versions require an external pullup resistor.
GND Ground
Active-Low Watchdog Output. The MAX6730/MAX6732/MAX6734 provide an open-
drain WDO output. The MAX6731/MAX6733/MAX6735 provide a push-pull WDO
output. WDO asserts low when no low-to-high or high-to-low transition occurs on
3
3
4
WDO WDI within the watchdog timeout period (t ) or if an undervoltage lockout
WD
condition exists for V 1, V 2, or RSTIN. WDO deasserts without a timeout period
CC
CC
when V 1, V 2, and RSTIN exceed their reset thresholds, or when the manual
CC
CC
reset input is deasserted. Open-drain versions require an external pullup resistor.
Active-Low Manual Reset Input. Drive MR low to force a reset. RST remains
asserted as long as MR is low and for the reset timeout period after MR releases
4
5
—
5
5
3
MR
high. MR has a 50kΩ pullup resistor to V 1; leave MR open or connect to V 1 if
CC
CC
unused.
Watchdog Input. If WDI remains high or low for longer than the watchdog timeout
period, the internal watchdog timer expires and the watchdog output asserts low.
The internal watchdog timer clears whenever RST asserts or a rising or falling edge
on WDI is detected. The watchdog has an initial watchdog timeout period (35s min)
after each reset event and a short timeout period (1.12s min) after the first valid
WDI transition. Floating WDI does not disable the watchdog timer function.
WDI
Primary Supply-Voltage Input. V 1 provides power to the device when it is greater
CC
6
6
4
8
6
V
1
CC
than V 2. V 1 is the input to the primary reset threshold monitor.
CC
CC
Secondary Supply-Voltage Input. V 2 provides power to the device when it is
CC
—
V
2
CC
greater than V 1. V 2 is the input to the secondary reset threshold monitor.
CC
CC
Undervoltage Reset Comparator Input. RSTIN provides a high-impedance
comparator input for the adjustable reset monitor. RST asserts low if the voltage at
—
—
7
RSTIN RSTIN drops below the 626mV internal reference voltage. Connect a resistive
voltage-divider to RSTIN to monitor voltages higher than 626mV. Connect RSTIN to
V
1 or V 2 if unused.
CC CC
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7