Low Cost Microprocessor
Supervisory Circuits
ADM705/ADM706/ADM707/ADM708
FEATURES
Guaranteed RESET valid with V
CC
= 1 V
190 μA quiescent current
Precision supply voltage monitor
4.65 V (ADM705/ADM707)
4.40 V (ADM706/ADM708)
200 ms reset pulse width
Debounced TTL/CMOS manual reset input (MR)
Independent watchdog timer (ADM705/ADM706)
1.60 sec timeout (ADM705/ADM706)
Active high reset output (ADM707/ADM708)
Voltage monitor for power-fail or low battery warning
Superior upgrade for MAX705 to MAX708
WATCHDOG
INPUT (WDI)
FUNCTIONAL BLOCK DIAGRAMS
WATCHDOG
TRANSITION
DETECTOR
V
CC
250μA
MR
V
CC
4.65V*
POWER-FAIL
INPUT (PFI)
1.25V
WATCHDOG
TIMER
WATCHDOG
OUTPUT (WDO)
RESET AND
WATCHDOG
TIMEBASE
RESET
GENERATOR
RESET
ADM705/
ADM706
POWER-FAIL
OUTPUT (PFO)
00088-001
00088-002
* VOLTAGE REFERENCE = 4.65V (ADM705), 4.40V (ADM706)
APPLICATIONS
Microprocessor systems
Computers
Controllers
Intelligent instruments
Critical microprocessor supply monitoring
V
CC
Figure 1. ADM705/ADM706
250μA
MR
V
CC
4.65V*
POWER-FAIL
INPUT (PFI)
1.25V
RESET
GENERATOR
RESET
RESET
ADM707/
ADM708
POWER-FAIL
OUTPUT (PFO)
* VOLTAGE REFERENCE = 4.65V (ADM707), 4.40V (ADM708)
Figure 2. ADM707/ADM708
GENERAL DESCRIPTION
The ADM705/ADM706/ADM707/ADM708 microprocessor
supervisory circuits are suitable for monitoring 5 V power
supplies/batteries and can also monitor microprocessor activity.
The ADM705/ADM706 provide power-supply monitoring
circuitry that generate a reset output during power-up, power-
down, and brownout conditions. The reset output remains
operational with V
CC
as low as 1 V. Independent watchdog
monitoring circuitry is also provided. This is activated if the
watchdog input has not been toggled within 1.60 seconds.
In addition, there is a 1.25 V threshold detector to warn of
power-failures, to detect low battery conditions, or to monitor an
additional power supply. An active low, debounced manual reset
input (MR) is also included.
The ADM705 and ADM706 are identical except for the reset
threshold monitor levels, which are 4.65 V and 4.40 V, respectively.
The ADM707 and ADM708 provide a similar functionality to
the ADM705 and ADM706 and only differ in that a watchdog
timer function is not available. Instead, an active high reset
output (RESET) is available as well as the active low reset output
(RESET). The ADM707 and ADM708 are identical except for
the reset threshold monitor levels, which are 4.65 V and 4.40 V,
respectively.
All parts are available in narrow 8-lead PDIP and 8-lead SOIC
packages.
Rev. G
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