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參數(shù)資料
| 型號： | REF19xGRU |
| 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) |
| 文件頁數(shù)： | 21/23頁 |
| 文件大?。?/td> | 238K |
| 代理商： | REF19XGRU |
REV. D
–21–
REF19x Series
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 applica-
tion are the OP295, the OP291 and the OP183/OP283.
1
m
F
REF19x
V
OUT
V
IN
GND
V
IN
100k
V
R
L
R
LW
SLEEP
V
IN
2
3
1
A1
R
LW
+V
SENSE
+V
OUT
FORCE
A1 = 1/2 OP292
1/2 OP283
Figure 23. A Low Dropout, Kelvin Connected Voltage
Reference
A Fail-Safe 5 V Reference
Some critical applications require a reference voltage to be
maintained constant, even with a loss of primary power. The
low standby power of the REF19x series and the switched out-
put 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, auto-
matically switching between the two as the power conditions
change.
The circuit in Figure 24 illustrates the concept, which borrows
from the switched output idea of Figure 21, again using the
REF19x device family output “wire-OR” capability. In this
case, since a constant 5 V reference voltage is desired for all
There is one application caveat that should be understood about
this circuit, which comes about due to the wire-OR nature.
Since U1 and U2 can only
source
current effectively, negative
going output voltage changes, which require the
sinking
of cur-
rent, will necessarily take longer than positive going changes. In
practice, this means that the circuit is quite fast when undergo-
ing a transition from 3.3 to 5 V, but the transition from 5 to
3.3 V will take longer. Exactly how much longer will be a func-
tion of the load resistance, R
L
,
seen at the output and the
typical 1
μ
F value of C2. In general, a conservative transition
time here will be on the order of several milliseconds for load
resistances in the range of 100
–1 k
. Note that for highest
accuracy at the new output voltage, several time constants
should be allowed (>7.6 time constants for <1/2 LSB error @
10 bits, for example).
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 circuit’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 regulators,
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 ampli-
fier, as shown in Figure 23. This method provides a means by
which the effects of wiring resistance voltage drops can be elimi-
nated. 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
U1
REF195
C1
0.1
m
F
V
, V
BAT
COMMON
V
COMMON
+5.000V
C3
1
m
F
U2
REF195
R5
100k
V
R6
100
V
C2
0.1
m
F
6
4
2
3
U3
AD820
R4
900k
V
C4
0.1
m
F
R2
100k
V
R3
10M
V
R1
1.1M
V
+V
BAT
+V
S
Q1
2N3904
7
Figure 24. A Fail-Safe 5 V Reference
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PDF描述 |
|---|---|
| REF19xGS | Precision Micropower, Low Dropout, Voltage References |
| REF194GRU | Precision Micropower, Low Dropout, Voltage References |
| REF195GRU | Precision Micropower, Low Dropout, Voltage References |
| REF191GP | Precision Micropower, Low Dropout, Voltage References |
| REF193GP | Precision Micropower, Low Dropout, Voltage References |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| REF19XGRU4 | 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout Voltage References |
| REF19XGS | 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout, Voltage References |
| REF19XSERIES | 制造商:AD 制造商全稱:Analog Devices 功能描述:Precision Micropower, Low Dropout, Voltage References |
| REF200 | 制造商:BB 制造商全稱:BB 功能描述:DUAL CURRENT SOURCE/CURRENT SINK |
| REF200_07 | 制造商:BB 制造商全稱:BB 功能描述:DUAL CURRENT SOURCE/CURRENT SINK |
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