AVR180
9
should detect the event, wake up and resume execution
where it left off.
Figure 7. Adding Hysteresis to Threshold Voltage
Hysteresis
Hysteresis in the low-voltage detector might be imple-
mented in the integrated circuit, or can be added with exter-
nal circuitry (Figure 7). This prevents the detector from
oscillating when used in battery applications.
Figure 8. Integrated Reset Circuit with Preset Threshold
Voltage
Figure 9. Integrated Reset Circuit with Adjustable Thresh-
old Voltage
Fixed/Adjustable Threshold Voltage
Some circuits offer the threshold voltage V
T
to be tuned by
external components, while others have a preset threshold
voltage reference. The use of a fixed threshold voltage IC
is shown in Figure 8.
The typical connection for externally tuned threshold volt-
age is shown in Figure 9. This device offers an internal volt-
age reference and a comparator. If the voltage at the input
pin is higher than the reference voltage, the output will be
activated. The threshold voltage is easily defined by a volt-
age divider, R1 and R2.
Notes:
1. Offered by Maxim Integrated Product, Inc.
2. Offered by Dallas Semiconductors
3. Offered by EM Microelectronic-Marin SA
4. A = expensive
B = moderate
C = inexpensive
RESET
R1
1 - 4K
W
V
CC
ISP
OPTIONAL
RESET
SWITCH
R1
R2
DETECTOR
LOGIC
V
CC
ISP
OPTIONAL
RESET
SWITCH
V
CC
RESET
GND
AVR
V
CC
RESET
GND
ISP
OPTIONAL
RESET
SWITCH
AVR
V
CC
RESET
GND
V
CC
IN
R1
R2
RESET
GND
V
CC
V
T
Table 3. Example Devices
Device
Features
ISP Support
Cost Level
(4)
MAX809
(1)
Fixed Threshold Voltage, Fixed Pulse Stretching
Yes
A
MAX811
(1)
Fixed Threshold Voltage, Fixed Pulse Stretching, Low Power, Manual Reset Input
Yes
A
MAX821
(1)
Fixed Threshold Voltage, Adjustable Pulse Stretching, Low Power
Yes
DS1811
(2)
Fixed Threshold Voltage, Fixed Pulse Stretching
Yes
DS1813/18
(2)
Fixed Threshold Voltage, Fixed Pulse Stretching, Feedback Monitor
No
V6301
(3)
Fixed Threshold Voltage, Fixed Pulse Stretching, Low Power, Low Cost
Yes
C
V6340
(3)
Fixed Threshold Voltage, No Pulse Stretching, Low Cost
Yes
C
Summary of Contents for AVR180
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