ADM6316/ADM6318/ADM6319/ADM6320/ADM6321/ADM6322

Data Sheet

Rev. J | Page 10 of 14

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/ADM6318/ADM6319/ADM6320/ADM6321/

ADM6322 are equipped with glitch rejection circuitry. The typical

ration 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 capacitor mounted close to

Both active low and active high reset outputs are guaranteed to

low as 0 V are possible. For an active low reset output, a resistor

connected between RESET and ground pulls the output low when

it is unable to sink current. For the active high case, a resistor

is unable to source current. A large resistance, such as 100 kΩ,

must be used so that it does not overload the reset output when

ADM6316/

ADM6318/

ADM6319

RESET

100kΩ

ADM6318/

ADM6319/

ADM6321/

ADM6322

RESET

100kΩ

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 19).

START

SET WDI

HIGH

PROGRAM

CODE

SUBROUTINE

SET WDI

LOW

RETURN

INFINITE LOOP:

WATCHDOG

TIMES OUT

RESET

Figure 19. Watchdog Flow Diagram

RESET

RESET

WDI

I/O

MR

ADM6316

MICROPROCESSOR

Figure 20. Typical Application Circuit