ADM8710 Data Sheet
Rev. 0 | Page 8 of 12
THEORY OF OPERATION
The ADM8710 is a compact, low power supervisory circuit
capable of monitoring up to four voltages in a multisupply
application.
The device includes two factory-set voltage threshold options
for monitoring 1.8 V and 3.3 V supplies. It also provides two
adjustable thresholds for monitoring voltages down to 0.62 V.
The ADM8710 is powered by IN
2
, which is a monitored voltage,
and therefore monitors up to four voltages. If a monitored voltage
drops below its associated threshold, the active low reset output
asserts low and remains low while either IN
1
or IN
2
remains
above 1.0 V.
Figure 11. Typical Applications Circuit
INPUT CONFIGURATION
The ADM8710 provides numerous monitor choices with
adjustable reset thresholds. Typically, the threshold voltage at
each adjustable IN
x
input is 0.62 V. To monitor a voltage greater
than 0.62 V, connect a resistor divider network to the circuit as
depicted in Figure 12, where
+
=
R2
R2R1
VV
INTH
62.0
Figure 12. Setting the Adjustable Monitor
The internal comparators each typically have a hysteresis of 0.3%
with respect to the reset threshold. This built-in hysteresis
improves the immunity of the device to ambient noise without
noticeably reducing the threshold accuracy. The ADM8710 is
unaffected by short input transients.
The ADM8710 is powered from the monitored IN
2
. Monitored
inputs are resistant to short power supply glitches. Figure 6 depicts
the ADM8710 glitch immunity data. To increase noise immunity
in noisy applications, place a 0.1 µF capacitor between the IN
2
input
and ground. Adding capacitance to IN
1
, IN
3
, and IN
4
also improves
noise immunity.
Do not allow unused monitor inputs to float or to be grounded.
Connect these inputs to a supply voltage greater than their specified
threshold voltages. In the case of unused IN
x
adjustable inputs,
limit the bias current by connecting a 1 MΩ series resistor between
the unused input and IN
2
.
RESET
OUTPUT CONFIGURATION
The
RESET
output asserts low when a monitored IN
x
voltage
drops below its voltage threshold. When all voltages rise above
the selected threshold level, the
RESET
signal remains low for
the reset timeout period. The
RESET
output is open drain with
a weak internal pull-up to the monitored IN
2
, typically 10 µA.
Many applications that interface with other logic devices do not
require an external pull-up resistor. However, if an external pull-up
resistor is required and it is connected to a voltage ranging from
0 V to 5.5 V, it overdrives the internal pull-up. Reverse current
flow from the external pull-up voltage to IN
2
is prevented by the
internal circuitry.
Figure 13. Interface with a Different Logic Supply Voltage
ADDITION OF MANUAL RESET
Use the circuit shown in Figure 14 to add manual reset to any of
the ADM8710 adjustable inputs. When the switch is closed, the
analog input shorts to ground and a
RESET
output commences.
The switch must remain open for a minimum of 35 ms for
the
RESET
output to deassert.
Figure 14. Addition of Manual Reset (IN
4
is an Adjustable Input)
MICROPROCESSOR
ADM8710
IN
1
IN
2
IN
3
IN
4
GND
RESET
3.3V
1.8V
0.9V
1.2V
10647-011
INTH
V
REF
= 0.62V
10647-012
ADM8710
RESET RESET
V
CC
5V
100kΩ
IN
2
= 3.3V
10647-013
ADM8710
IN
1
IN
2
IN
3
IN
4
GND
RESET
R1
R2
V
IN4
10647-014
