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

5V

R1

R2

1.25V

PFI

PFO

ADP3367

–

+

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

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

R1

R2

5V

MICROPROCESSOR

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

5V

MICROPROCESSOR

Figure 21. Bidirectional Input/Output RESET