APPLICATION NOTES
BENEFITS OF AN 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 microprocessor reset
circuit’s power supply. The possibility of a malfunction during a
power failure is greatly reduced because the SGM803/
SGM809/SGM810 series can operate effectively even when
there are large degradations of the supply voltages. Another
advantage of the SGM803/ SGM809/SGM810 series is its very
accurate internal voltage reference circuit. These benefits
combine to produce an exceptionally reliable voltage monitor
circuit.
INTERFACING TO OTHER DEVICES’ OUTPUT
The SGM803/SGM809/SGM810 series is designed to integrate
with as many devices as possible and, therefore, has a
standard output dependent on V
CC
. This enables the parts to
be used in both 3 V and 5 V, or any nominal voltage within the
minimum and maximum specifications for V
CC
. This design
simplifies interfacing this device to other devices.
ENSURING A VALID RESET OUTPUT DOWN TO
V
CC
= 0 V
When V
CC
falls below 1.0 V, the SGM803/SGM809
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 100kΩ
resistor should be
connected from
RESET
to ground.
V
CC
INTERFACING TO MICROPROCESSORS WITH
MULTIPLE INTERRUPTS
In a number of cases, it is necessary to interface many
interrupts from different devices (for example, thermal, altitude,
and velocity sensors). The SGM803/SGM809/SGM810 can
easily be integrated into existing interrupt-handling circuits, as
shown in Figure 1, or can be used as a standalone device.
V
CC
SGM809
RESET
GND
PRIORITY ENCODER
74LS147
4-LINE BCD TO
MICROPROCESSOR
Figure 2. Ensuring a Valid Reset Output Down to V
CC
= 0V
V
CC
V
CC
SGM809
RESET
GND
OTHER SENSING
DEVICES
Figure 1. Interfacing to Microprocessors with Multiple
Interrupts
７
SGM803/809/810
SGMICRO [ Shengbang Microelectronics Co, Ltd ]
