ADM13305
Rev. 0 | Page 10 of 12
THEORY OF OPERATION
The ADM13305 is a dual voltage supervisor designed to
monitor two supplies and provide a reset signal to DSP and
microprocessor-based systems.
There are five models available, all of which feature a combina-
tion of internally pretrimmed undervoltage threshold options
for monitoring 1.8 V, 2.5 V, 3.3 V, and 5 V supplies. There is also
an adjustable input option with an undervoltage threshold of 0.6 V.
The ADM13305-18, ADM13305-25, and ADM13305-33 have
two internally fixed thresholds, while the ADM13305-4 and
ADM13305-5 offer one internally fixed threshold and one
externally programmable threshold via a resistor string. See
the Ordering Guide for a list of all available options.
INPUT CONFIGURATION
The ADM13305 is powered through V
DD
. To increase noise
immunity in noisy applications, place a 0.1 μF capacitor
between the V
DD
input and ground.
The SENSEv inputs are resistant to short power supply glitches.
Do not allow an unused SENSEv input to float or to be grounded,
instead connect it to a supply voltage greater than its specified
threshold voltage.
Typically, the threshold voltage at each adjustable SENSEv input
is 0.6 V. To monitor a voltage greater than 0.6 V, connect a resistor
divider network to the device as depicted in Figure 13, where,
⎟
⎠
⎞
⎜
⎝
⎛
+
=
R2
R2R1
V
MONITERED
V6.0
06922-012
R1
R2
MONITORED VOLTAGE
V
REF
= 0.6V
Figure 13. Setting the Adjustable Monitor
RESET OUTPUT
The reset outputs are guaranteed to be in the correct state for
V
DD
down to 1.1 V. During power-up,
RESET
is asserted when
the supply voltage becomes greater than 1.1 V.
06922-013
SENSEv
V
(NOM)
0
1
V
IT–
RESET
t
d
t
d
t
t
Figure 14. Reset Timing Diagram
Once the supplies monitored at the SENSEv pins rise above
their associated threshold level, the
RESET
signal remains low
for the reset timeout period before deasserting. Subsequently, if
either of the supplies monitored by the SENSEv pins falls below
its associated threshold the
RESET
output reasserts.
The ADM13305 features both an active-low, push-pull
RESET
output and an active-high, push-pull RESET output.
WATCHDOG TIMER
The ADM13305 features a watchdog timer that monitors
microprocessor activity. A timer circuit is cleared with every
low-to-high or high-to-low logic transition on the watchdog
input pin (WDI). If the timer counts through the preset
watchdog timeout period of 1.6 sec,
RESET
is asserted, as
shown in . Figure 15
The microprocessor is required to toggle the WDI pin to avoid
being reset. Therefore, failure of the microprocessor to toggle
WDI within the timeout period indicates a code execution error
and the reset pulse generated restarts the microprocessor in a
known state. The watchdog timer can be disabled by leaving
WDI floating.
06922-014
0
1
RESET
0
1
WDI
t
WD
t
d
t
t
Figure 15. Watchdog Timing Diagram
