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參數(shù)資料
| 型號： | ADR291GR |
| 廠商： | ANALOG DEVICES INC |
| 元件分類： | 基準電壓源/電流源 |
| 英文描述： | Low Noise Micropower Precision Voltage References |
| 中文描述： | 1-OUTPUT THREE TERM VOLTAGE REFERENCE, 2.5 V, PDSO8 |
| 封裝： | MS-012AA, SOIC-8 |
| 文件頁數(shù)： | 13/15頁 |
| 文件大小： | 199K |
| 代理商： | ADR291GR |
ADR290/ADR291/ADR292
REV. B
–13–
APPLICATIONS SECTION
A Negative Precision Reference without Precision Resistors
In many current-output CMOS DAC applications, where the
output signal voltage must be of the same polarity as the reference
voltage, it is often required to reconfigure a current-switching
DAC into a voltage-switching DAC through the use of a 1.25 V
reference, an op amp and a pair of resistors. Using a current-
switching DAC directly requires the need for an additional
operational amplifier at the output to reinvert the signal. A
negative voltage reference is then desirable from the point that
an additional operational amplifier is not required for either
reinversion (current-switching mode) or amplification (voltage-
switching mode) of the DAC output voltage. In general, any
positive voltage reference can be converted into a negative volt-
age reference through the use of an operational amplifier and a
pair of matched resistors in an inverting configuration. The dis-
advantage to that approach is that the largest single source of
error in the circuit is the relative matching of the resistors used.
The circuit illustrated in Figure 3 avoids the need for tightly
matched resistors with the use of an active integrator circuit. In
this circuit, the output of the voltage reference provides the
input drive for the integrator. The integrator, to maintain circuit
equilibrium adjusts its output to establish the proper relationship
between the reference
’
s V
OUT
and GND. Thus, any negative
output voltage desired can be chosen by simply substituting for
the appropriate reference IC. One caveat with this approach
should be mentioned: although rail-to-rail output amplifiers
work best in the application, these operational amplifiers require
a finite amount (mV) of headroom when required to provide
any load current. The choice for the circuit
’
s negative supply
should take this issue into account.
A1
100
+5V
–
5V
1k
1 F
100k
V
OUT
GND
V
IN
ADR29x
–
V
REF
A1 = 1/2 OP291,
1/2 OP295
1 F
Figure 3. A Negative Precision Voltage Reference Uses No
Precision Resistors
A Precision Current Source
Many times in low power applications, the need arises for a pre-
cision current source that can operate on low supply voltages.
As shown in Figure 4, any one of the devices in the ADR29x
family of references can be configured as a precision current
source. The circuit configuration illustrated is a floating current
source with a grounded load. The reference
’
s output voltage is
bootstrapped across R
SET,
which sets the output current into the
load. With this configuration, circuit precision is maintained for
load currents in the range from the reference
’
s supply current,
typically 12
μ
A to approximately 5 mA.
1 F
V
OUT
GND
V
IN
ADR29x
I
OUT
R
L
I
SY
ADJUST
R1
P1
R
SET
Figure 4. A Precision Current Source
High Voltage Floating Current Source
The circuit of Figure 5 can be used to generate a floating
current source with minimal self heating. This particular con-
figuration can operate on high supply voltages determined by
the breakdown voltage of the N-channel JFET.
+V
S
OP90
ADR29
X
V
IN
GND
E231
SILICONIX
2N3904
2.10k
–
V
S
Figure 5. High Voltage Floating Current Source
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). Force and sense connections also referred to as
Kelvin connections, offer a convenient method of eliminating the
effects of voltage drops in circuit wires. Load currents flowing
through wiring resistance produce an error (V
ERROR
= R I
L
) at
the load. However, the Kelvin connection of Figure 6, 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.
相關(guān)PDF資料 |
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| ADR290FR-RELL | Low Noise Micropower Precision Voltage References |
| ADR290GR-RELL | Low Noise Micropower Precision Voltage References |
| ADR290GRU-RELL | Low Noise Micropower Precision Voltage References |
| ADR291ER-RELL | Low Noise Micropower Precision Voltage References |
| ADR291FR-RELL | Low Noise Micropower Precision Voltage References |
相關(guān)代理商/技術(shù)參數(shù) |
參數(shù)描述 |
|---|---|
| ADR291GR-REEL | 制造商:Analog Devices 功能描述:V-Ref Precision 2.5V 5mA 8-Pin SOIC N T/R |
| ADR291GR-REEL7 | 制造商:Analog Devices 功能描述:V-Ref Precision 2.5V 5mA 8-Pin SOIC N T/R 制造商:Rochester Electronics LLC 功能描述:LOW NOISE MICROPWR PRECISION VOLT. REF. - Tape and Reel |
| ADR291GR-RELL | 制造商:AD 制造商全稱:Analog Devices 功能描述:Low Noise Micropower Precision Voltage References |
| ADR291GRU | 制造商:Analog Devices 功能描述:V-Ref Precision 2.5V 5mA 8-Pin TSSOP Tube 制造商:Analog Devices 功能描述:IC VOLT REF |
| ADR291GRU-REEL | 制造商:AD 制造商全稱:Analog Devices 功能描述:Low Noise Micropower Precision Voltage References |
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