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參數(shù)資料
| 型號： | SP704 |
| 英文描述： | Low Power Microprocessor Supervisory with Battery Switch-Over |
| 中文描述： | 低功耗微處理器監(jiān)控與電池開關(guān)過 |
| 文件頁數(shù)： | 12/16頁 |
| 文件大?。?/td> | 216K |
| 代理商： | SP704 |
SP703/704DS/07
SP703/704 Low Power Microprocessor Supervisory
12
Copyright 2000 Sipex Corporation
Allowable Backup Power-Source
Batteries
Lithium batteries work very well as backup
batteries due to very low self-discharge rate and
high energy density. Single lithium batteries
with open-circuit voltages of 3.0V to 3.6V are
ideal. Any battery with an open-circuit voltage
less than the minimum reset threshold plus 0.3V
can be connected directly to the V
input
of this series with no additional circuitry; see
Figure 8
. However, batteries with open-circuit
voltages that are greater than this value cannot
be used for backup, as current is sourced into
V
OUT
through the diode
(D1 in Figure 9)
when
V
CC
is close to the reset threshold.
Operation Without a Backup Power
Source
If a backup power source is not used, ground
V
and connect V
to V
. Since there is
no need to switch over to any backup power
source, V
does not need to be switched. A
direct connection to V
eliminates any voltage
drops across the switch which may push V
OUT
below V
CC
.
Replacing the Backup Battery
The backup battery can be removed while V
remains valid, without danger of triggering
RESET/RESET. As long as V
stays above the
reset threshold, battery-backup mode cannot be
entered.
Adding Hysteresis to the Power-Fail
Comparator
Hysteresis adds a noise margin to the power-fail
comparator and prevents repeated triggering
of PFO when V
is close to its trip point.
Figure 14
shows how to add hysteresis to the
power-fail comparator. Select the ratio of R
1
and R
such that PFI sees 1.25V when V
falls
to its trip point (V
). R
adds the hysteresis.
It will typically be an order of magnitude greater
(about 10 times) than R
or R
. The current
through R
and R
should be at least 1
μ
A to
ensure that the 25nA (max) PFI input current
does not shift the trip point. R
should be larger
than 10K
so it does not load down the PFO pin.
Capacitor C1 adds additional noise rejection.
Monitoring a Negative Voltage
The power-fail comparator can be used to
monitor a negative supply rail using the circuit
of
Figure 15
. When the negative rail is valid,
PFO is low. When the negative supply voltage
drops, PFO goes high. This circuit's accuracy
is affected by the PFI threshold tolerance, the
V
CC
voltage, and the resistors, R1 and R2.
Figure 14. Adding Hysteresis to the POWER-FAIL
Comparator
PFI
PFO
R
3
*C
1
R
2
R
1
V
IN
connect to
μ
P
V
CC
+5V
GND
PFO
V
IN
+5V
0V0V
V
L
V
H
V
TRIP
*optional
V
TRIP
=
R
2
R
1
+ R
2
V
H
=
R
2
|| R
3
R
1
+ R
2
|| R
3
1.25
R
2
=V
L
- 1.25
R
1
5.0 - 1.25
R
3
+
1.25
1.25
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| SP704CN | Low Power Microprocessor Supervisory with Battery Switch-Over |
| SP704CP | Low Power Microprocessor Supervisory with Battery Switch-Over |
| SP704EN | Low Power Microprocessor Supervisory with Battery Switch-Over |
| SP704EP | Low Power Microprocessor Supervisory with Battery Switch-Over |
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相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| SP7041-HAR | 制造商:Methode Electronics Inc 功能描述: |
| SP7041-JN | 制造商:Methode Electronics Inc 功能描述: |
| SP7044 | 制造商:Semi Circuits 功能描述: |
| SP704CN | 制造商:Exar Corporation 功能描述: |
| SP704CP | 制造商:SIPEX 制造商全稱:Sipex Corporation 功能描述:Low Power Microprocessor Supervisory with Battery Switch-Over |
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