ADM706P/ADM706R/ADM706S/ADM706T, ADM708R/ADM708S/ADM708T

Rev. C | Page 12 of 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

3.3V

WDO

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

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 is generated.

V

RESET

GND

MR

PFI

WDI

PFO

RESET

X

+3V/+3.3V

R1

R2

ADM706R/

ADM706S/

ADM706T

MICROPROCESSOR

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

RESET

GND

RESET

GND

BUFFERED

RESET

+3V/+3.3V

ADM706R/ADM706S/

ADM706T/ADM708R/

ADM708S/ADM708T

MICROPROCESSOR

Figure 23. Bidirectional Input/Output RESET