ADM6316 Analog Devices, ADM6316 Datasheet - Page 10

• Manufacturer Part Number: ADM6316
• Description: Supervisory Circuit with Watchdog, Manual Reset, and Active-Low/Push-Pull
• Manufacturer: Analog Devices

Specifications of ADM6316

• Batt-backup-flg: No
• Manual Reset Capability: Yes
• Package: SOT
• Power Fail Indicator: No
• Reset Threshold Summary: 26 Options--2.5 to 5V
• Reset Output-stage: Active-Low/Push-Pull
• Min Reset Timeout (ms): 1,1120,140,20
• Typ Watchdog Timeout (ms): 102,1600,25,600,6.3
• Watchdog Timer: Yes

ADM6316/ADM6317/ADM6318/ADM6319/ADM6320/ADM6321/ADM6322
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.
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 circuitry.
The typical performance characteristic in Figure 14 plots V
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
capacitor mounted close to V
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
as low as 0 V are possible. For an active-low reset output, a
CC
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
CC
provides additional glitch
ADM6317/
ADM6318/
ADM6319/
ADM6321/
ADM6322
CC
V
CC
CC
= 0 V
pulls the output high
CC
= 0 V
RESET
100kΩ
CC
Rev. E | 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 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).
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
RESET