參數(shù)資料
型號(hào)： REF19XES3
廠商： Analog Devices, Inc.
英文描述： Precision Micropower, Low Dropout Voltage References
中文描述： 精密微功耗，低壓差電壓基準(zhǔn)
文件頁(yè)數(shù)： 21/24頁(yè)
文件大?。?/td> 364K
代理商： REF19XES3
REV. E
REF19x Series
–21–
U1
REF195
C1
0.1 F
V
S
, V
BAT
COMMON
V
OUT
COMMON
5.000V
C3
1 F
U2
REF195
R5
100k
R6
100
C2
0.1 F
6
4
2
3
U3
AD820
R4
900k
C4
0.1 F
R2
100k
R3
10M
R1
1.1M
+V
BAT
+V
S
Q1
2N3904
7
Figure 11. A Fail-Safe 5 V Reference
Kelvin Connections
In many portable instrumentation applications where PC board
cost and area go hand-in-hand, circuit interconnects are very
often of dimensionally minimum width. These narrow lines
can cause large voltage drops if the voltage reference is required
to provide load currents to various functions. In fact, a cir-
cuit
’
s interconnects can exhibit a typical line resistance of
0.45 m
/square (1 oz. Cu, for example). In those applications
where these devices are configured as low dropout voltage regu-
lators, these wiring voltage drops can become a large source of
error. To circumvent this problem, force and sense connections
can be made to the reference through the use of an operational
amplifier, as shown in Figure 10. This method provides a means
by which the effects of wiring resistance voltage drops can be
eliminated. Load currents flowing through wiring resistance
produce an I-R error (I
LOAD
R
WIRE
) at the load. However, the
Kelvin connection overcomes the problem by including the
wiring resistance within the forcing loop of the op amp. Since the
op amp senses the load voltage, op amp loop control forces the
output to compensate for the wiring error and to produce the
correct voltage at the load. Depending on the reference device
chosen, operational amplifiers that can be used in this application
are the OP295, the OP291, and the OP183/OP283.
1 F
REF19x
V
IN
GND
V
OUT
V
IN
100k
R
L
R
LW
SLEEP
V
IN
2
3
1
A1
R
LW
+V
OUT
SENSE
+V
FORCE
A1 = 1/2 OP295
1/2 OP292
1/2 OP283
Figure 10. A Low Dropout, Kelvin Connected
Voltage Reference
A Fail-Safe 5 V Reference
Some critical applications require a reference voltage to be main-
tained constant, even with a loss of primary power. The low standby
power of the REF19x series and the switched output capability
allow a
“
fail-safe
”
reference configuration to be implemented
rather easily. This reference maintains a tight output voltage
tolerance for either a primary power source (ac line derived) or
a standby (battery derived) power source, automatically switching
between the two as the power conditions change.
The circuit in Figure 11 illustrates the concept, which borrows
from the switched output idea of Figure 8, again using the REF19x
device family output
“
wire-OR
”
capability. In this case, since a
constant 5 V reference voltage is desired for all conditions, two
REF195 devices are used for U1 and U2, with their ON/OFF
switching controlled by the presence or absence of the primary
dc supply source, V
S
. V
BAT
is a 6 V battery backup source that sup-
plies power to the load only when V
S
fails. For normal (V
S
present)
power conditions, V
BAT
sees only the 15
μ
A (max) standby current
drain of U1 in its OFF state.
In operation, it is assumed that for all conditions either U1 or U2
is ON and a 5 V reference output is available. With this voltage
constant, a scaled down version is applied to the comparator IC
U3, providing a fixed 0.5 V input to the (
–
) input for all power
conditions. The R1
–
R2
divider provides a signal to the U3 (+)
input proportional to V
S
, which switches U3 and U1/U2 dependent
upon the absolute level of V
S
. Op amp U3 is configured here as
a comparator with hysteresis, which provides for clean, noise free
output switching. This hysteresis is important to eliminate rapid
switching at the threshold due to V
S
ripple. Further, the device
chosen is the AD820, a rail-to-rail output device that provides
HI and LO output states within a few mV of V
S
and ground for
accurate thresholds and compatible drive for U2 for all V
S
condi-
tions. R3 provides positive feedback for circuit hysteresis, changing
the threshold at the (+) input as a function of U3
’
s output.
相關(guān)PDF資料
PDF描述
REF19XFS3 Precision Micropower, Low Dropout Voltage References
REF19XGRU4 Precision Micropower, Low Dropout Voltage References
REF43 +2.5V Low Power Precision Voltage Reference
REF-43 +2.5V Low Power Precision Voltage Reference
REF43BJ +2.5V Low Power Precision Voltage Reference
相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
REF19XFS 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout, Voltage References
REF19XFS3 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout Voltage References
REF19XGBC 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout, Voltage References
REF19XGP 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout, Voltage References
REF19XGRU 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout, Voltage References
發(fā)布緊急采購(gòu)，3分鐘左右您將得到回復(fù)。

采購(gòu)需求

(若只采購(gòu)一條型號(hào)，填寫(xiě)一行即可)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

發(fā)布成功！您可以繼續(xù)發(fā)布采購(gòu)。也可以進(jìn)入我的后臺(tái)，查看報(bào)價(jià)

*型號(hào) *數(shù)量 廠商 批號(hào) 封裝
添加更多采購(gòu)

我的聯(lián)系方式

*
*
*