Datasheet

ADM706P/ADM706R/ADM706S/ADM706T, ADM708R/ADM708S/ADM708T
Rev. C | Page 12 of
06435-020
16
APPLICATIONS INFORMATION
A typical operating circuit is shown in Figure 20. The unregulated
dc input supply is monitored using the PFI input via the resistive
divider network. Resistor R1 and Resistor R2 are to be selected
so that when the supply voltage drops below the desired level
(for example, 5 V), the voltage on PFI drops below the 1.25 V
threshold, thereby generating an interrupt to the microprocessor.
Monitoring the preregulator input gives additional time to
execute an orderly shutdown procedure before power is lost.
RESET
GND
MR
PFI
WDI
PFO
RESET
V
CC
3.3V
WDO
V
CC
I/O LINE
INTERRUPT
NMI
MANUAL
GND
RESET
GND
IN
OUT
ADM666A
MICROPROCESSOR
ADM706R/
ADM706S/
ADM706T
UNREGULATED
DC
Figure 20. Typical Application Circuit
Microprocessor activity is monitored using the WDI input. This
is driven using an output line from the processor. The software
routines toggle this line at least once every 1.6 seconds. If a problem
occurs and this line is not toggled,
WDO
goes low and a nonmask-
able interrupt is generated. This interrupt routine is to be used
to clear the problem.
If, in the event of inactivity on the WDI line, a system reset is
required, the
WDO
output is to be connected to the input as
shown in . Figure 21
06435-021
RESET
GND
I/O LINE
MR
PFI
WDI
WDO
RESET
MICROPROCESSOR
ADM706R/
ADM706S/
ADM706T
Figure 21.
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 22. The two sensing resistors, R1 and
R2, are selected such that the voltage on PFI drops below 1.25 V at
the minimum acceptable input supply. The
PFO
output can be
connected to the
MR
input 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 i
s generated.
V
06435-022
RESET
GND
MR
PFI
WDI
PFO
RESET
X
+3V/+3.3V
V
CC
R1
R2
ADM706R/
ADM706S/
ADM706T
MICROPROCESSOR
Figure 22. Monitoring 3 V/3.3 V and an Additional Supply, V
X
MICROPROCESSORS WITH BIDIRECTIONAL RESET
To prevent contention for microprocessors with a bidirectional
reset line, a current limiting resistor is to be inserted between
the ADM706R/ADM706S/ADM706T, ADM708R/ADM708S/
ADM708T
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 23
06435-023
RESET
GND
RESET
GND
BUFFERED
RESET
+3V/+3.3V
V
CC
ADM706R/ADM706S/
ADM706T/ADM708R/
ADM708S/ADM708T
MICROPROCESSOR
Figure 23. Bidirectional Input/Output
RESET