ADM6823 Analog Devices, ADM6823 Datasheet - Page 10

• Manufacturer Part Number: ADM6823
• Description: Low Voltage Supervisory Circuit with Watchdog, Manual Reset and Active-Low, Push-Pull Reset Output
• Manufacturer: Analog Devices

Specifications of ADM6823

• Batt-backup-flg: No
• Manual Reset Capability: Yes
• Package: SOT
• Power Fail Indicator: No
• Reset Threshold Summary: 9 Options--1.58 to 4.63V
• Reset Output-stage: Active-Low/Push-Pull
• Min Reset Timeout (ms): 140
• Typ Watchdog Timeout (ms): 1600
• Watchdog Timer: Yes

ADM6821/ADM6822/ADM6823/ADM6824/ADM6825
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-high-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 ADM682x are equipped with glitch rejection
circuitry. The typical performance characteristic in Figure 11
plots V
The curves show combinations of transient magnitude and
duration for which a reset is not generated for the 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 bigger in magnitude or duration, a reset is generated. An
optional 0.1 μF bypass capacitor mounted close to V
additional 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
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 connected between RESET and V
the output high 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
ADM6822/
ADM6823/
ADM6824/
ADM6825
CC
V
CC
CC
as low as 0 V are possible. For an active-low reset
GND
transient duration versus. the transient magnitude.
CC
Figure 16. Ensuring Reset Valid to V
as low as 1 V. However, by using an external
RESET
100kΩ
CC
TRANSIENTS
CC
ADM6821/
ADM6824/
ADM6825
is above 1 V.
CC
V
CC
= 0 V
GND
CC
= 0 V
RESET
CC
CC
100kΩ
provides
pulls
Rev. 0 | Page 10 of 12
WATCHDOG SOFTWARE CONSIDERATIONS
In implementing the microprocessor’s watchdog strobe code,
quickly switching WDI low-high and then high-low
(minimizing WDI high time) is desirable for current
consumption reasons. However, a more effective way of using
the watchdog function can be considered.
A low-high-low WDI pulse within a given subroutine prevents
the watchdog from timing out. However, if the subroutine
becomes stuck in an infinite loop, the watchdog could not
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.
SUBROUTINE
PROGRAM
RETURN
SET WDI
SET WDI
START
CODE
MR
HIGH
LOW
ADM6823
Figure 18. Typical Application Circuit
Figure 17. Watchdog Flow Diagram
V
CC
RESET
WDI
RESET
I/O
INFINITE LOOP:
WATCHDOG
TIMES OUT
μP
RESET