ADM6316/ADM6317/ADM6318/ADM6319/ADM6320/ADM6321/ADM6322

Data Sheet

Rev. F | Page 10 of 16

APPLICATIONS INFORMATION

WATCHDOG INPUT CURRENT

To minimize watchdog input current (and minimize overall

power consumption), leave WDI low for the majority of the

watchdog timeout period. When driven high, WDI can draw

as much as 160 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 reset is

not asserted when the watchdog timer times out.

To avoid unnecessary resets caused by fast power supply transients,

the ADM6316/ADM6317/ADM6318/ADM6319/ADM6320/

ADM6321/ADM6322 are equipped with glitch rejection circuitry.

transient duration vs. the transient magnitude. The curves show

combinations of transient magnitude and duration for which a

reset is not generated for 4.63 V and 2.93 V reset threshold

parts. For example, with the 2.93 V threshold, a transient that

goes 100 mV below the threshold and lasts 8 µs typically does

not cause a reset, but if the transient is any larger in magnitude

or duration, a reset is generated. An optional 0.1 µF bypass

rejection.

Both active-low and active-high reset outputs are guaranteed

resistor with push-pull configured reset outputs, valid outputs

resistor connected between RESET and ground pulls the output

low when it is unable to sink current. For the active-high case, a

when it is unable to source current. A large resistance, such as

100 kΩ, should be used so that it does not overload the reset

ADM6316/

ADM6318/

ADM6319

RESET

100k

Ω

ADM6317/

ADM6318/

ADM6319/

ADM6321/

ADM6322

RESET

100

kΩ

WATCHDOG SOFTWARE CONSIDERATIONS

In implementing the microprocessor’s 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 20).

START

SET WDI

HIGH

PROGRAM

CODE

SUBROUTINE

SET WDI

LOW

RETURN

INFINITE LOOP:

WATCHDOG

TIMES OUT

RESET

Figure 20. Watchdog Flow Diagram

RESET

RESET

WDI

I/O

MR

ADM6316

MICROPROCESSOR

Figure 21. Typical Application Circuit