ADM809-5L/ADM809-5S
Rev. B | Page 7 of 8
THEORY OF OPERATION
INTERFACING TO OUTPUT OF OTHER DEVICES
The ADM809-5L/ADM809-5S are designed to integrate with as
many devices as possible and, therefore, have an output dependent
on V
CC
. Because of this design approach, interfacing these devices
to other devices is simplified.
ENSURING A VALID RESET OUTPUT DOWN TO
V
CC
= 0 V
When V
CC
falls below 0.8 V, the ADM809-5L/ADM809-5S
RESET
no longer sinks current. A high impedance CMOS logic
input connected to
RESET
may, therefore, drift to undetermined
logic levels. To eliminate this problem, a 100 kΩ resistor should
be connected from
RESET
to ground.
GND
100kΩ
ADM809-5L/
ADM809-5S
V
CC
V
CC
RESET
00090-010
Figure 10. Ensuring a Valid
RESET
Output Down to V
CC
= 0 V
BENEFITS OF A VERY ACCURATE RESET THRESHOLD
In other microprocessor supervisory circuits, tolerances in supply
voltages lead to an overall increase in
RESET
tolerance levels
due to the deterioration of the
RESET
circuit power supply of
the microprocessor. The possibility of a malfunction during
a power failure is greatly reduced because the ADM809-5L/
ADM809-5S can operate effectively even when there are large
degradations of the supply voltages. Another advantage of the
ADM809-5L/ADM809-5S series is its very accurate internal
voltage reference circuit. These benefits combine to produce
an exceptionally reliable voltage monitor circuit.
INTERFACING TO MICROPROCESSORS WITH
MULTIPLE INTERRUPTS
In a number of cases, it is necessary to interface to many
interrupts from different devices (for example, from thermal,
attitude, and velocity sensors). The ADM809-5L/ADM809-5S
can be easily integrated into existing interrupt-handling circuits
(see Figure 13) or used as standalone devices.
4-LINE BCD TO
MICROPROCESSOR
ADM809
GND
V
CC
V
CC
RESET
OTHER SENSING
DEVICES
PRIORITY ENCODER
74LS147
00090-011
Figure 11. Interfacing to Microprocessors with Multiple Interrupts
ADM809-5L/
ADM809-5S
V
CC
100nF
3.3V
RESETGND
21
3
47kΩ
47kΩ
00090-012
Figure 12. Alternative Application Circuit with Extra Decoupling
ADM809-5L/
ADM809-5S
V
CC
100nF
3.3V
RESETGND
21
3
22kΩ
00090-013
Figure 13. Additional Decoupling Can Be Achieved Using a 100 nF Capacitor
Between V
CC
and Ground
