Datasheet
ADM705/ADM706/ADM707/ADM708
Rev. G | Page 10 of 12
APPLICATIONS INFORMATION
A typical application circuit is shown in Figure 18. The
unregulated dc input supply is monitored using PFI via the
resistive divider network. Resistor R1 and Resistor R2 should
be selected so that when the supply voltage drops below the
desired level (such as 8 V), the voltage on PFI drops below
the 1.25 V threshold, thereby generating an interrupt to the
microprocessor. Monitoring the preregulator input provides
additional time to execute an orderly shutdown procedure
before power is lost.
7V TO 15V
INPUT POWER
MICROPROCESSOR
5
V
V
CC
R1
R2
1.25V
PFI
PFO
ADP3367
–
+
00088-020
RESET
ADM705/ADM706/
ADM707/ADM708
Figure 18. Typical Application Circuit
Microprocessor activity is monitored using WDI. This is driven
using an output line from the processor. The software routines
should toggle this line at least once every 1.60 seconds. If a
problem occurs and this line is not toggled,
WDO
goes low and
a nonmaskable interrupt is generated. This interrupt routine can be
used to clear the problem.
If, in the event of inactivity on the WDI line, a system reset
is required,
WDO
should be connected to
MR
, as shown in
Figure 19.
ADM705/
ADM706
RESET
GND
I/O LINE
MICROPROCESSOR
MR
WDI
WDO
RESET
00088-021
Figure 19.
RESET
From
WDO
MONITORING ADDITIONAL SUPPLY LEVELS
It is possible to use the power-fail comparator to monitor a
second supply as shown in Figure 20. The two sensing resistors,
R1 and R2, are selected so that the voltage on PFI drops below
1.25 V at the minimum acceptable input supply.
PFO
can be
connected to
MR
so that a reset is generated when the supply
drops out of tolerance. In this case, if either supply drops out
of tolerance, a reset is generated.
ADM705/
ADM706
RESET
GND
MR
PFI
PFO
RESET
V
CC
R1
R2
V
X
5
V
00088-022
MICROPROCESSOR
Figure 20. Monitoring 5 V and an Additional Supply, V
X
MICROPROCESSOR WITH BIDIRECTIONAL RESET
To prevent contention for microprocessors with a bidirectional
reset line, a current limiting resistor should be inserted between
the ADM70x
RESET
output pin and the microprocessor
RESET
pin. This limits the current to a safe level if there are conflicting
output reset levels. A suitable resistor value is 4.7 kΩ. If the reset
output is required for other uses, it should be buffered, as shown in
Figure 21.
ADM70x
RESET
GND
RESET
GND
BUFFERED
RESET
5
V
V
CC
00088-023
MICROPROCESSOR
Figure 21. Bidirectional Input/Output
RESET