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전자부품 반도체 검색엔진( 무료 PDF 다운로드 ) - 데이터시트뱅크

ADR421BRZ-REEL7-RevJ 데이터 시트보기 (PDF) - Analog Devices

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ADR421BRZ-REEL7 Datasheet PDF : 24 Pages
Data Sheet
KELVIN CONNECTIONS
In many portable instrumentation applications where PC board
cost and area are important considerations, circuit intercon-
nects are often narrow. 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 mΩ/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 flow-
ing through wiring resistance produce an error (VERROR = R × IL)
at the load. However, the Kelvin connection in Figure 43
overcomes the problem by including the wiring resistance
within the forcing loop of the op amp. Because 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.
VIN
2
ADR420/
ADR421/
ADR423/
ADR425
VOUT 6
GND
4
RLW
VIN
RLW
A1
A1 = OP191
VOUT
SENSE
VOUT
FORCE
RL
Figure 43. Advantage of Kelvin Connection
ADR420/ADR421/ADR423/ADR425
DUAL-POLARITY REFERENCES
Dual-polarity references can easily be made with an op amp and
a pair of resistors. In order not to defeat the accuracy obtained
by the ADR42x, it is imperative to match the resistance toler-
ance and the temperature coefficient of all components.
VIN
1µF 0.1µF 2
VIN
VOUT 6
+5V
R1
U1
10k
R2
10k
ADR425
+10V
GND TRIM 5
V+
4
U2
OP1177
–5V
V–
R3
5k
–10V
Figure 44. +5 V and −5 V Reference Using ADR425
+2.5V
+10V
2
VIN
VOUT 6
U1
ADR425
R1
5.6k
GND
4
TRIM 5
R2
5.6k
–2.5V
V+
U2
OP1177
V–
–10V
Figure 45. +2.5 V and −2.5 V Reference Using ADR425
Rev. J | Page 19 of 24
 

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