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RCV420JP Schematic ( PDF Datasheet ) - Burr-Brown Corporation

Teilenummer RCV420JP
Beschreibung Precision 4mA to 20mA CURRENT LOOP RECEIVER
Hersteller Burr-Brown Corporation
Logo Burr-Brown Corporation Logo 




Gesamt 10 Seiten
RCV420JP Datasheet, Funktion
®
RCV420
RCV420
Precision 4mA to 20mA
CURRENT LOOP RECEIVER
FEATURES
q COMPLETE 4-20mA TO 0-5V CONVERSION
q INTERNAL SENSE RESISTORS
q PRECISION 10V REFERENCE
q BUILT-IN LEVEL-SHIFTING
q ±40V COMMON-MODE INPUT RANGE
q 0.1% OVERALL CONVERSION ACCURACY
q HIGH NOISE IMMUNITY: 86dB CMR
DESCRIPTION
The RCV420 is a precision current-loop receiver de-
signed to convert a 4–20mA input signal into a 0–5V
output signal. As a monolithic circuit, it offers high
reliability at low cost. The circuit consists of a pre-
mium grade operational amplifier, an on-chip precision
resistor network, and a precision 10V reference. The
RCV420 features 0.1% overall conversion accuracy,
86dB CMR, and ±40V common-mode input range.
The circuit introduces only a 1.5V drop at full scale,
which is useful in loops containing extra instrument
burdens or in intrinsically safe applications where
APPLICATIONS
q PROCESS CONTROL
q INDUSTRIAL CONTROL
q FACTORY AUTOMATION
q DATA ACQUISITION
q SCADA
q RTUs
q ESD
q MACHINE MONITORING
transmitter compliance voltage is at a premium. The
10V reference provides a precise 10V output with a
typical drift of 5ppm/°C.
The RCV420 is completely self-contained and offers a
highly versatile function. No adjustments are needed
for gain, offset, or CMR. This provides three important
advantages over discrete, board-level designs: 1) lower
initial design cost, 2) lower manufacturing cost, and
3) easy, cost-effective field repair of a precision circuit.
RCV420
V+
16
–In 1
300k
RS
75
CT 2
RS
75
+In 3
300k
V– Ref In
4 12
99k
92k
11.5k
1.01k
+10V
Ref
100k
13
Rcv
Com
5
Ref
Com
15 Rcv fB
14 Rcv Out
11 Ref Out
10 Ref fB
8 Ref Trim
7 Ref Noise Reduction
International Airport Industrial Park • Mailing Address: PO Box 11400, Tucson, AZ 85734 • Street Address: 6730 S. Tucson Blvd., Tucson, AZ 85706 • Tel: (520) 746-1111 • Twx: 910-952-1111
Internet: http://www.burr-brown.com/ • FAXLine: (800) 548-6133 (US/Canada Only) • Cable: BBRCORP • Telex: 066-6491 • FAX: (520) 889-1510 • Immediate Product Info: (800) 548-6132
©1988 Burr-Brown Corporation
PDS-1837E
RCV420Printed in U.S.A. October, 1997
®






RCV420JP Datasheet, Funktion
tions, the voltage reference output trim procedure can be
used to null offset errors at the output of the RCV420. The
voltage reference trim circuit is discussed under “Voltage
Reference.”
When the voltage reference is not used for level shifting or
when large offset adjustments are required, the circuit in
Figure 3 can be used for offset adjustment. A low impedance
on the Rcv Com pin is required to maintain high CMR.
ZERO ADJUSTMENT
Level shifting the RCV420 output voltage can be achieved
using either the Ref In pin or the Rcv Com pin. The
disadvantage of using the Ref In pin is that there is an 8:1
voltage attenuation from this pin to the output of the RCV420.
Thus, use the Rcv Com pin for large offsets, because the
voltage on this pin is seen directly at the output. Figure 4
shows the circuit used to level-shift the output of the RCV420
–In 1
CT 2
+In 3
RCV420
13
15
14
5
12
±150mV adjustment at output.
OPA237
VO
+15V
100k
1k
100k
–15V
FIGURE 3. Optional Output Offset Nulling Using External
Amplifier.
using the Rcv Com pin. It is important to use a low-output
impedance amplifier to maintain high CMR. With this method
of zero adjustment, the Ref In pin must be connected to the
Rcv Com pin.
MAINTAINING COMMON-MODE REJECTION
Two factors are important in maintaining high CMR: (1)
resistor matching and tracking (the internal resistor network
does this) and (2) source impedance. CMR depends on the
accurate matching of several resistor ratios. The high accu-
racies needed to maintain the specified CMR and CMR
temperature coefficient are difficult and expensive to reli-
ably achieve with discrete components. Any resistance im-
balance introduced by external circuitry directly affects
CMR. These imbalances can occur by: mismatching sense
resistors when gain is decreased, adding resistance in the
feedback path when gain is increased, and adding series
resistance on the Rcv Com pin.
The two sense resistors are laser-trimmed to typically match
within 0.01%; therefore, when adding parallel resistance to
decrease gain, take care to match the parallel resistance on
each sense resistor. To maintain high CMR when increasing
the gain of the RCV420, keep the series resistance added to
the feedback network as small as possible. Whether the Rcv
Com pin is grounded or connected to a voltage reference for
level shifting, keep the series resistance on this pin as low as
possible. For example, a resistance of 20on this pin
degrades CMR from 86dB to approximately 80dB. For
applications requiring better than 86dB CMR, the circuit
shown in Figure 5 can be used to adjust CMR.
PROTECTING THE SENSE RESISTOR
The 75sense resistors are designed for a maximum con-
tinuous current of 40mA, but can withstand as much as
250mA for up to 0.1s (see absolute maximum ratings).
There are several ways to protect the sense resistor from
–In 1
CT 2
+In 3
12
Use 10V Ref for +
and 10V Ref with INA105 for –.
RCV420
5
13
15
14
11
10
+10V
VO = (0.3125)(I IN) + VZERO
VO
25
3 INA105
1
6
–10V
VZERO
OPA237
±5V adjustment
at output.
10k
10k
50k
RCV420
13
Procedure:
1. Connect CMV to CT.
2. Adjust potentiometer for near zero
at the output.
1k
1k
OPA237
1k
1k
200
CMR
Adjust
FIGURE 4. Optional Zero Adjust Circuit.
FIGURE 5. Optional Circuit for Externally Trimming CMR.
®
RCV420
6

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