ADM708ARMZ-REEL(2016) View Datasheet(PDF) - Analog Devices
Part Name
Description
Manufacturer
ADM708ARMZ-REEL Datasheet PDF : 8 Pages
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ADM705/ADM706/ADM707/ADM708
APPLICATIONS INFORMATION
A typical application circuit is shown in Figure 18. The un-
regulated dc input supply is monitored using PFI via the resistive
divider network. Resistor R1 and Resistor R2 must be selected
so 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
5V
ADP3367
R1
VCC
MICROPROCESSOR
1.25V –
PFO
INTERRUPT
+
PFI
R2
RESET
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
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 clear the problem.
If, in the event of inactivity on the WDI line, a system reset is
required, WDO must connect to MR as shown in Figure 19.
RESET
ADM705/
ADM706
WDI
MR
WDO
GND
RESET
MICROPROCESSOR
I/O LINE
Figure 19. RESET From WDO
Data Sheet
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 the voltage on PFI drops below 1.25 V at
the minimum acceptable input supply. PFO can connect to MR so
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.
VX
5V
VCC
RESET
ADM705/
R1
ADM706
PFI
R2
MR
PFO
GND
RESET
MICROPROCESSOR
Figure 20. Monitoring 5 V and an Additional Supply, VX
MICROPROCESSOR WITH BIDIRECTIONAL RESET
To prevent contention for microprocessors with a bidirectional
reset line, a current limiting resistor must be inserted between
the ADM705/ADM706/ADM707/ADM708 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 must be buffered, as shown in Figure 21.
5V
BUFFERED
RESET
VCC
ADM70x
RESET
GND
MICROPROCESSOR
RESET
GND
Figure 21. Bidirectional Input/Output RESET
Rev. H | Page 10 of 12
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