ADM705/ADM706/ADM707/ADM708

Data Sheet

Rev. H | Page 10 of 12

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

MICROPROCESSOR

5V

R1

R2

1.25V

PFI

PFO

ADP3367

–

+

RESET

INTERRUPT

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.

ADM705/

ADM706

RESET

GND

I/O LINE

MICROPROCESSOR

MR

WDI

WDO

RESET

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 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.

ADM705/

ADM706

RESET

GND

MR

PFI

PFO

RESET

R1

R2

5V

MICROPROCESSOR

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.

ADM70x

RESET

GND

RESET

GND

BUFFERED

RESET

5V

MICROPROCESSOR

Figure 21. Bidirectional Input/Output RESET