adm6318cy29arjz-r7 Analog Devices, Inc., adm6318cy29arjz-r7 Datasheet - Page 10

• Manufacturer Part Number: adm6318cy29arjz-r7
• Description: Supervisory Circuit With Watchdog And Manual Reset In 5-lead Sot-23
• Manufacturer: Analog Devices, Inc.

ADM6316/ADM6317/ADM6318/ADM6319/ADM6320/ADM6321/ADM6322
APPLICATION 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.
NEGATIVE-GOING V
To avoid unnecessary resets caused by fast power supply transients,
the ADM6316/ADM6317/ADM6318/ADM6319/ADM6320/
ADM6321/ADM6322 are equipped with glitch rejection cir-
cuitry. The typical performance characteristic in Figure 14
plots V
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 V
glitch rejection.
ENSURING RESET VALID TO V
Both active-low and active-high reset outputs are guaranteed
to be valid for V
resistor with push-pull configured reset outputs, valid outputs
for V
resistor connected between RESET and ground pulls the output
low when it is unable to sink current. For the active-high case, a
resistor connected between RESET and V
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
output when V
ADM6316/
ADM6318/
ADM6319
CC
V
CC
as low as 0 V are possible. For an active-low reset output, a
CC
transient duration vs. the transient magnitude. The
Figure 19. Ensuring Reset Valid to V
CC
CC
RESET
is above 1 V.
as low as 1 V. However, by using an external
100kΩ
CC
TRANSIENTS
ADM6317/
ADM6318/
ADM6319/
ADM6321/
ADM6322
CC
CC
V
provides additional
CC
CC
= 0 V
pulls the output high
CC
= 0 V
RESET
100kΩ
Rev. C | Page 10 of 16
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 timing out. However, if the subroutine
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
SUBROUTINE
MR
PROGRAM
SET WDI
SET WDI
RETURN
ADM6316
START
CODE
HIGH
LOW
Figure 21. Typical Application Circuit
Figure 20. Watchdog Flow Diagram
V
CC
RESET
WDI
MICROPROCESSOR
RESET
I/O
INFINITE LOOP:
WATCHDOG
TIMES OUT
Figure 20).
RESET