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PDF ADM8324 Data sheet ( Hoja de datos )
| Número de pieza | ADM8324 | |
| Descripción | (ADM8323 / ADM8324) Supervisory Circuits | |
| Fabricantes | Analog Devices | |
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Data Sheet
Supervisory Circuits with Windowed
Watchdog and Manual Reset in 5-Lead SOT-23
ADM8323/ADM8324
FEATURES
Windowed watchdog, 8 timeout options
26 reset threshold options
2.5 V to 5 V in 100 mV increments
4 reset timeout options
1 ms, 20 ms, 140 ms, and 1120 ms (minimum)
Manual reset input
Open-drain or push-pull RESET outputs
Low power consumption
Specified over wide temperature range (−40°C to +125°C)
Qualified for automotive applications
5-lead SOT-23 package
APPLICATIONS
Automotive
Microprocessor systems
Computers
Controllers
Intelligent instruments
Portable equipment
FUNCTIONAL BLOCK DIAGRAMS
ADM8323
VCC
VREF
RESET
GENERATOR
VCC
RESET
MR DEBOUNCE
WINDOWED
WATCHDOG
DETECTOR
GND
ADM8324
WDI
Figure 1.
VCC
VREF
MR DEBOUNCE
RESET
GENERATOR
WINDOWED
WATCHDOG
DETECTOR
RESET
GENERAL DESCRIPTION
The ADM8323/ADM8324 are supervisory circuits that monitor
power supply voltage levels and code execution integrity in
microprocessor-based systems. An on-chip watchdog timer
checks for activity within a preset timeout window. A reset
signal can also be asserted by an external push-button switch
through a manual reset input. The RESET output is either push-
pull (ADM8323) or open-drain (ADM8324).
A watchdog failure results in a low output on the RESET pin.
A failure can be triggered either by a fast watchdog error
(watchdog pulses too close together) or by a slow watchdog
error (no watchdog pulse within the timeout period). This
effectively gives a window in which to observe the watchdog
GND
WDI
Figure 2.
pulse. The watchdog timeout is measured from the last falling
edge of the watchdog input (WDI). There are eight different
watchdog windows available, as shown in Table 5.
Each device is available in a choice of 26 reset threshold options
from 2.5 V to 5 V in 100 mV increments. There are also four
reset timeout options of 1 ms, 20 ms, 140 ms, and 1120 ms
(minimum).
The ADM8323/ADM8324 are available in a 5-lead SOT-23
package and typically consume only 10 μA, making them
suitable for use in low power portable applications.
Rev. 0
Document Feedback
Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Analog Devices for its use, nor for any infringements of patents or other
rights of third parties that may result from its use. Specifications subject to change without notice. No
license is granted by implication or otherwise under any patent or patent rights of Analog Devices.
Trademarksandregisteredtrademarksarethepropertyoftheirrespectiveowners.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
©2013 Analog Devices, Inc. All rights reserved.
Technical Support
www.analog.com
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Data Sheet
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
Table 2.
Parameter
VCC
All Other Pins
Output Current (RESET)
Operating Temperature Range
Storage Temperature Range
θJA Thermal Impedance, SOT-23
Lead Temperature
Soldering (10 sec)
Vapor Phase (60 sec)
Infrared (15 sec)
Rating
−0.3 V to +6 V
−0.3 V to (VCC + 0.3 V)
20 mA
−40°C to +125°C
−65°C to +150°C
270°C/W
300°C
215°C
220°C
ADM8323/ADM8324
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
Rev. 0 | Page 5 of 16
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Data Sheet
APPLICATIONS INFORMATION
WATCHDOG INPUT CURRENT
There is no way to disable the windowed watchdog functional-
ity. Do not leave the WDI pin floating because this is not a valid
mode of operation. If the WDI pin is not in a defined state at
startup, this can lead to high supply current until the microproces-
sor is enabled and takes control of the WDI pin. A solution to
this is to add a 100 kΩ pull-up or pull-down resistor on the
WDI pin to hold it in a defined state until the microprocessor is
enabled.
NEGATIVE GOING VCC TRANSIENTS
To avoid unnecessary resets caused by fast power supply transients,
the ADM8323/ADM8324 are equipped with glitch rejection
circuitry. The typical performance characteristic in Figure 14
plots VCC transient duration vs. reset threshold overdrive. The
curves show combinations of reset threshold overdrive and
duration for which a reset is not generated for 5 V, 4.63 V, and
2.93 V reset threshold devices. For example, with the 2.93 V
threshold, a transient that goes 100 mV below the threshold and
lasts 80 µs typically does not cause a reset, but if the transient is
any larger in reset threshold overdrive or duration, a reset
generates. An optional 0.1 µF bypass capacitor mounted near
VCC provides additional glitch rejection.
ADM8323/ADM8324
ENSURING RESET VALID TO VCC = 0 V
The reset output is guaranteed valid for VCC as low as 0.9 V.
However, by using an external resistor with the push-pull
configured reset output on the ADM8323, a valid output for VCC
as low as 0 V is possible. For this active low reset output, a resistor
connected between RESET and ground pulls the output low
when it is unable to sink current. Use a large resistance, such as
100 kΩ, so that it does not overload the reset output when VCC
is above 0.9 V.
VCC
ADM8323
RESET
100kΩ
Figure 24. Ensuring RESET Valid to VCC = 0 V
VCC
RESET
ADM8323
MR WDI
RESET
MICROPROCESSOR
I/O
Figure 25. ADM8323 Typical Application Circuit
Rev. 0 | Page 11 of 16
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