Data Sheet

ADM8316/ADM8318/ADM8319/ADM8320/ADM8321/ADM8322

Rev. 0 | Page 11 of 16

APPLICATIONS INFORMATION

WATCHDOG INPUT CURRENT

To minimize the watchdog input current, leave WDI low for the

majority of the watchdog timeout period. When driven high,

WDI can draw as much as 100 µA. Pulsing WDI low to high to

low at a low duty cycle reduces the effect of the large input

current. When WDI is unconnected, a window comparator

disconnects the watchdog timer from the reset output circuitry

so that a reset is not asserted when the watchdog timer times out.

To avoid unnecessary resets caused by fast power supply transients,

the ADM8316/ADM8318/ADM8319/ADM8320/ADM8321/

ADM8322 are equipped with glitch rejection circuitry. The typical

duration vs. reset threshold overdrive. The curves show

combinations of reset threshold overdrive and duration for

which a reset is not generated for 5 V, 4.63 V, and 2.93 V reset

threshold devices. For example, with the 2.93 V threshold, a

transient that goes 100 mV below the threshold and lasts 80 µs

typically does not cause a reset, but if the transient is any larger

in reset threshold overdrive or duration, a reset generates. An

additional glitch rejection.

Both active low and active high reset outputs are guaranteed

external resistor with push-pull configured reset outputs, valid

output, a resistor connected between RESET and ground pulls

the output low when it is unable to sink current. For an active

pulls the output high when it is unable to source current. Use a

large resistance, such as 100 kΩ, so that it does not overload the

WATCHDOG SOFTWARE CONSIDERATIONS

In implementing the microprocessor watchdog strobe code,

quickly switching WDI low to high and then high to low (mini-

mizing WDI high time) is desirable for current consumption

reasons. However, a more effective way of using the watchdog

function can be considered.

A low to high to low WDI pulse within a given subroutine

prevents the watchdog from timing out. However, if the sub-

routine becomes stuck in an infinite loop, the watchdog cannot

detect this because the subroutine continues to toggle WDI. A

more effective coding scheme for detecting this error involves

using a slightly longer watchdog timeout. In the program that

calls the subroutine, WDI is set high. The subroutine sets WDI

low when it is called. If the program executes without error, WDI

is toggled high and low with every loop of the program. If the

subroutine enters an infinite loop, WDI is kept low, the watchdog

times out, and the microprocessor is reset (see Figure 23).

Figure 23. Watchdog Flow Diagram

Figure 24. Typical Application Circuit

ADM8316/

ADM8318/

ADM8319

RESET

100k

Ω

ADM8318/

ADM8319/

ADM8321/

ADM8322

RESET

100

kΩ

START

SET WDI

HIGH

PROGRAM

CODE

SUBROUTINE

SET WDI

LOW

RETURN

INFINITE LOOP:

WATCHDOG

TIMES OUT

RESET

RESET

RESET

WDI

I/O

MR

ADM8316

MICROPROCESSOR