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参数资料
| 型号： | LM810-2.63MDC |
| 厂商： | NATIONAL SEMICONDUCTOR CORP |
| 元件分类： | 电源管理 |
| 英文描述： | 1-CHANNEL POWER SUPPLY SUPPORT CKT, UUC |
| 封装： | DIE |
| 文件页数： | 13/16页 |
| 文件大小： | 281K |
| 代理商： | LM810-2.63MDC |
Applications Information
Benefits of Precision Reset Thresholds
A microprocessor supply supervisor must provide a reset
output within a predictable range of the supply voltage. A
common threshold range is between 5% and 10% below the
nominal supply voltage. The 4.63V and 3.08V options of the
LM809/810 use highly accurate circuitry to ensure that the
reset threshold occurs only within this range (for 5V and 3.3V
supplies). The other voltage options have the same tight
tolerance to ensure a reset signal for other narrow monitor
ranges. See
Table 1 for examples of how the standard reset
thresholds apply to 3V, 3.3V, and 5V nominal supply volt-
ages.
TABLE 1. Reset Thresholds Related to Common
Supply Voltages
Reset
Threshold
3.0V
3.3V
5.0V
4.63 ± 3%
90 - 95%
4.38 ± 3%
85 - 90%
4.00 ± 3%
78 - 82%
3.08 ± 3%
90 - 95%
2.93 ± 3%
86 - 90%
2.63 ± 3%
85 - 90%
77 - 81%
2.45 ± 3%
79 - 84%
72 - 76%
Ensuring a Valid Reset Output Down to V
CC =0V
When V
CC falls below 1V, the LM809 RESET output no
longer sinks current. A high-impedance CMOS logic input
connected to RESET can therefore drift to undetermined
voltages. To prevent this situation, a 100k
resistor should
be connected from the RESET output to ground, as shown in
A 100k
pull-up resistor to V
CC is also recommended for the
LM810, if RESET is required to remain valid for V
CC < 1V.
Negative-Going V
CC Transients
The
LM809/810
are
relatively
immune
to
short
negative-going transients or glitches on V
CC. Figure 2 shows
the maximum pulse width a negative-going V
CC transient
can have without causing a reset pulse. In general, as the
magnitude of the transient increases, going further below the
threshold, the maximum allowable pulse width decreases.
Typically, for the 4.63V and 4.38V version of the LM809/810,
aV
CC transient that goes 100mV below the reset threshold
and lasts 20s or less will not cause a reset pulse. A 0.1 F
bypass capacitor mounted as close as possible to the V
CC
pin will provide additional transient rejection.
Interfacing to Ps with Bidirectional Reset Pins
Microprocessors with bidirectional reset pins, such as the
Motorola 68HC11 series, can be connected to the LM809
RESET output. To ensure a correct output on the LM809
even when the microprocessor reset pin is in the opposite
state, connect a 4.7k
resistor between the LM809 RESET
output and the P reset pin, as shown in
Figure 3. Buffer the
LM809 RESET output to other system components.
10105710
FIGURE 1. RESET Valid to V
CC = Ground Circuit
10105709
FIGURE 2. Maximum Transient Duration without
Causing a Reset Pulse vs. Reset Comparator
Overdrive
10105711
FIGURE 3. Interfacing to Microprocessors with
Bidirectional Reset I/O
LM809/LM810
www.national.com
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相关代理商/技术参数 |
参数描述 |
|---|---|
| LM810A-2.63 E WAF | 制造商:Texas Instruments 功能描述: |
| LM810A-2.93 E WAF | 制造商:Texas Instruments 功能描述: |
| LM810A-3.08 E WAF | 制造商:Texas Instruments 功能描述: |
| LM810A-4.00 E WAF | 制造商:Texas Instruments 功能描述: |
| LM810A-4.38 E WAF | 制造商:Texas Instruments 功能描述: |
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