RCV420
1
RCV420
Precision 4mA to 20mA
CURRENT LOOP RECEIVER
APPLICATIONS
q
PROCESS CONTROL
q
INDUSTRIAL CONTROL
q
FACTORY AUTOMATION
q
DATA ACQUISITION
q
SCADA
q
RTUs
q
ESD
q
MACHINE MONITORING
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
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.
DESCRIPTION
The RCV420 is a precision current-loop receiver de-
signed to convert a 420mA input signal into a 05V
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
R
S
75
R
S
75
1
2
3
In
16
4
12
V+
V
Ref In
C
T
+In
100k
RCV420
1.01k
99k
11.5k
300k
300k
+10V
Ref
15
14
11
10
8
7
Rcv f
B
Rcv Out
Ref Out
Ref f
B
Ref Trim
Ref Noise Reduction
13
5
Rcv
Com
Ref
Com
92k
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
RCV420
1988 Burr-Brown Corporation
PDS-837E
Printed in U.S.A. October, 1997
2
RCV420
SPECIFICATIONS
ELECTRICAL
At T = +25
C and V
S
=
15V, unless otherwise noted.
RCV420KP, JP
CHARACTERISTICS
MIN
TYP
MAX
UNITS
GAIN
Initial
0.3125
V/mA
Error
0.05
0.15
% of span
Error--JP Grade
0.25
% of span
vs Temp
15
ppm/
C
Nonlinearity
(1)
0.0002
0.002
% of span
OUTPUT
Rated Voltage (I
O
= +10mA, 5mA)
10
12
V
Rated Current (E
O
= 10V)
+10, 5
mA
Impedance (Differential)
0.01
Current Limit (To Common)
+49, 13
mA
Capacitive Load
1000
pF
(Stable Operation)
INPUT
Sense Resistance
74.25
75
75.75
Input Impedance (Common-Mode)
200
k
Common-Mode Voltage
40
V
CMR
(2)
70
80
dB
vs Temp (DC) (T
A
= T
MIN
to T
MAX
)
76
dB
AC 60Hz
80
dB
OFFSET VOLTAGE (RTO)
(3)
Initial
1
mV
vs Temp
10
V/
C
vs Supply (
11.4V to
18V)
74
90
dB
vs Time
200
V/mo
ZERO ERROR
(4)
Initial
0.025
0.075
% of span
Initial--JP Grade
0.15
% of span
vs Temp
10
ppm of
span/
C
OUTPUT NOISE VOLTAGE
f
B
= 0.1Hz to 10Hz
50
Vp-p
f
O
= 10kHz
800
nV/
Hz
DYNAMIC RESPONSE
Gain Bandwidth
150
kHz
Full Power Bandwidth
30
kHz
Slew Rate
1.5
V/
s
Settling Time (0.01%)
10
s
VOLTAGE REFERENCE
Initial
9.99
10.01
V
Trim Range
(5)
4
%
vs Temp
5
ppm/
C
vs Supply (
11.4V to
18V)
0.0002
%/V
vs Output Current (I
O
= 0 to +10mA)
0.0002
%/mA
vs Time
15
ppm/kHz
Noise (0.1Hz to 10Hz)
5
Vp-p
Output Current
+10, 2
mA
POWER SUPPLY
Rated
15
V
Voltage Range
(6)
5, +11.4
18
V
Quiescent Current (V
O
= 0V)
3
4
mA
TEMPERATURE RANGE
Specification
0
+70
C
Operation
25
+85
C
Storage
40
+85
C
Thermal Resistance,
JA
80
C/W
NOTES: (1) Nonlinearity is the max peak deviation from best fit straight line. (2) With 0 source impedance on Rcv Com pin. (3) Referred to output with all inputs
grounded including Ref In. (4) With 4mA input signal and Voltage Reference connected (includes V
OS
, Gain Error, and Voltage Reference Errors). (5) External trim
slightly affects drift. (6) I
O
Ref = 5mA, I
O
Rcv = 2mA.
RCV420
3
Supply ...............................................................................................
22V
Input Current, Continuous ................................................................ 40mA
Input Current Momentary, 0.1s ........................... 250mA, 1% Duty Cycle
Common-Mode Input Voltage, Continuous .......................................
40V
Lead Temperature (soldering, 10s) ............................................... +300
C
Output Short Circuit to Common (Rcv and Ref) ..................... Continuous
NOTE: (1) Stresses above these ratings may cause permanent damage.
ABSOLUTE MAXIMUM RATINGS
(1)
V+
Rcv f
Rcv Out
Rcv Com
Ref In
Ref Out
Ref f
NC
In
C
+In
V
Ref Com
NC
Ref Noise Reduction
Ref Trim
1
2
3
4
5
6
7
8
16
15
14
13
12
11
10
9
T
B
B
PIN CONFIGURATION
ORDERING INFORMATION
PERFORMANCE
PRODUCT
GRADE
PACKAGE
RCV420KP
0
C to +70
C
16-Pin Plastic DIP
RCV420JP
0
C to +70
C
16-Pin Plastic DIP
Top View
DIP
The information provided herein is believed to be reliable; however, BURR-BROWN assumes no responsibility for inaccuracies or omissions. BURR-BROWN assumes
no responsibility for the use of this information, and all use of such information shall be entirely at the user's own risk. Prices and specifications are subject to change
without notice. No patent rights or licenses to any of the circuits described herein are implied or granted to any third party. BURR-BROWN does not authorize or warrant
any BURR-BROWN product for use in life support devices and/or systems.
PACKAGE INFORMATION
PACKAGE DRAWING
PRODUCT
PACKAGE
NUMBER
(1)
RCV420KP
16-Pin Plastic DIP
180
RCV420JP
16-Pin Plastic DIP
180
NOTE: (1) For detailed drawing and dimension table, please see end of data
sheet, or Appendix C of Burr-Brown IC Data Book.
4
RCV420
TYPICAL PERFORMANCE CURVES
At T
A
= +25
C, V
S
=
15V, unless otherwise noted.
STEP RESPONSE
NO LOAD
SMALL SIGNAL RESPONSE
R
L
=
, C
L
= 1000pF
SMALL SIGNAL RESPONSE
NO LOAD
POSITIVE COMMON-MODE VOLTAGE RANGE
vs POSITIVE POWER SUPPLY VOLTAGE
Positive Power Supply Voltage (V)
Positive Common-Mode Range (V)
80
70
60
50
40
30
11
12
13
14
15
16
17
18
19
20
Max Rating = 40V
V
S
= 5V to 20V
T
A
= 55C
T
A
= +25C
T
A
= +125C
11.4
NEGATIVE COMMON-MODE VOLTAGE RANGE
vs NEGATIVE POWER SUPPLY VOLTAGE
Negative Power Supply Voltage (V)
Negative Common-Mode Range (V)
80
70
60
50
40
30
20
10
5
20
Max Rating = 40V
+V
S
= +11.4V to +20V
T
A
= +25C
T
A
= 55C to +125C
10
15
COMMON-MODE REJECTION
vs FREQUENCY
Frequency (Hz)
CMR (dB)
100
80
60
40
1
10
100
1k
10k
100k
POWER-SUPPLY REJECTION
vs FREQUENCY
Frequency (Hz)
PSR (dB)
100
80
60
40
1
10
100
1k
10k
100k
90
V+
V
RCV420
5
75
75
R
S
R
S
+In 3
C
T
In 1
I
IN
420mA
16
4
+10V
Reference
5
Ref Com
13
Rcv Com
V+
V
12 Ref In
15 Rcv f
14 Rcv Out
B
V
O
(05V)
7 Ref Noise Reduction
8 Ref Trim
10 Ref f
B
11 Ref Out
1F
1F
RCV420
2
R
X
R
X
C
T
3
2
1
15
14
Rcv Out
R
1
NOTE: (1) Typical values. See text.
0.5% Gain
Adjustment
10k
(1)
200
(1)
10k
(1)
RCV420
+In
In
FIGURE 2. Optional Gain Adjustment.
necessary level shifting. If the Ref In pin is not used for level
shifting, then it must be grounded to maintain high CMR.
GAIN AND OFFSET ADJUSTMENT
Figure 2 shows the circuit for adjusting the RCV420 gain.
Increasing the gain of the RCV420 is accomplished by
inserting a small resistor in the feedback path of the ampli-
fier. Increasing the gain using this technique results in CMR
degradation, and therefore, gain adjustments should be kept
as small as possible. For example, a 1% increase in gain is
typically realized with a 125
resistor, which degrades
CMR by about 6dB.
A decrease in gain can be achieved by placing matched
resistors in parallel with the sense resistors, also shown in
Figure 2. The adjusted gain is given by the following
expression
V
OUT
/I
IN
= 0.3125
x
R
X
/(R
X
+ R
S
).
A 1% decrease in gain can be achieved with a 7.5k
resistor. It is important to match the parallel resistance on
each sense resistor to maintain high CMR. The TCR mis-
match between the two external resistors will effect gain
error drift and CMR drift.
There are two methods for nulling the RCV420 output offset
voltage. The first method applies to applications using the
internal 10V reference for level shifting. For these applica-
FIGURE 1. Basic Power Supply and Signal Connections.
THEORY OF OPERATION
Refer to the figure on the first page. For 0 to 5V output with
420mA input, the required transimpedance of the circuit is:
V
OUT
/I
IN
= 5V/16mA = 0.3125V/mA.
To achieve the desired output (0V for 4mA and 5V for
20mA), the output of the amplifier must be offset by an
amount:
V
OS
= (4mA)(0.3125V/mA) = 1.25V.
The input current signal is connected to either +In or In,
depending on the polarity of the signal, and returned to
ground through the center tap, C
T
. The balanced input--two
matched 75
sense resistors, R
S
--provides maximum rejec-
tion of common-mode voltage signals on C
T
and true differ-
ential current-to-voltage conversion. The sense resistors
convert the input current signal into a proportional voltage,
which is amplified by the differential amplifier. The voltage
gain of the amplifier is:
A
D
= 5V/(16mA)(75
) = 4.1667V/V.
The tee network in the feedback path of the amplifier
provides a summing junction used to generate the required
1.25V offset voltage. The input resistor network provides
high-input impedance and attenuates common-mode input
voltages to levels suitable for the operational amplifier's
common-mode signal capabilities.
BASIC POWER SUPPLY
AND SIGNAL CONNECTIONS
Figure 1 shows the proper connections for power supply and
signal. Both supplies should be decoupled with 1
F tanta-
lum capacitors as close to the amplifier as possible. To avoid
gain and CMR errors introduced by the external circuit,
connect grounds as indicated, being sure to minimize ground
resistance. The input signal should be connected to either
+In or In, depending on its polarity, and returned to ground
through the center tap, C
T
. The output of the voltage refer-
ence, Ref Out, should be connected to Ref In for the
6
RCV420
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
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 20
on 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 75
sense 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
FIGURE 4. Optional Zero Adjust Circuit.
FIGURE 5. Optional Circuit for Externally Trimming CMR.
FIGURE 3. Optional Output Offset Nulling Using External
Amplifier.
+In
C
T
3
2
1
15
14
V
RCV420
In
12
13
5
+15V
OPA237
15V
O
100k
100k
1k
150mV adjustment at output.
+In
C
T
3
2
1
15
14
V
RCV420
In
12
13
5
OPA237
O
50k
10k
10k
Use 10V Ref for +
and 10V Ref with INA105 for .
10
11
5
6
1
3
2
INA105
10V
V
ZERO
5V adjustment
at output.
V
O
= (0.3125)(I
IN
) + V
ZERO
+10V
OPA237
13
1k
RCV420
200
CMR
Adjust
1k
1k
1k
Procedure:
1. Connect CMV to C
2. Adjust potentiometer for near zero
T
.
at the output.
RCV420
7
+In
C
T
3
2
1
15
14
V
RCV420
In
8
10
11
O
400mV adjustment at output of reference, and 50mV
adjustment at output of receiver if reference is used for
level shifting.
V
REF
20k
2
3
15
14
V
RCV420
O
1
2
3
15
14
V
RCV420
O
1
2
3
15
14
V
RCV420
O
1
V
RX
R
X
420mA
a) R
X
= (V+)/40mA 75
420mA
420mA
2N3970
200
R
X
b) R
X
set for 30mA current limit at 25C.
f
1
V+
V+
V+
c) f
1
is 0.032A, Lifflefuse Series 217 fast-acting fuse.
overcurrent conditions exceeding these specifications. Refer
to Figure 6. The simplest and least expensive method is a
resistor as shown in Figure 6a. The value of the resistor is
determined from the expression
R
X
= V
CC
/40mA 75
and the full scale voltage drop is
V
RX
= 20mA
x
R
X
.
For a system operating off of a 32V supply R
X
= 725
and
V
RX
= 14.5V. In applications that cannot tolerate such a
large voltage drop, use circuits 6b or 6c. In circuit 6b a
power JFET and source resistor are used as a current limit.
The 200
potentiometer, R
X
, is adjusted to provide a current
limit of approximately 30mA. This circuit introduces a
14V drop at full scale. If only a very small series voltage
drop at full scale can be tolerated, then a 0.032A series 217
fast-acting fuse should be used, as shown in Figure 6c.
For automatic fold-back protection, use the circuit shown in
Figure 15.
VOLTAGE REFERENCE
The RCV420 contains a precision 10V reference. Figure 8
shows the circuit for output voltage adjustment. Trimming
the output will change the voltage drift by approximately
0.007ppm/
C per mV of trimmed voltage. Any mismatch in
TCR between the two sides of the potentiometer will also
affect drift, but the effect is divided by approximately 5. The
trim range of the voltage reference using this method is
typically
400mV. The voltage reference trim can be used to
trim offset errors at the output of the RCV420. There is an
8:1 voltage attenuation from Ref In to Rcv Out, and thus the
trim range at the output of the receiver is typically
50mV.
The high-frequency noise (to 1MHz) of the voltage refer-
ence is typically 1mVp-p. When the voltage reference is
used for level shifting, its noise contribution at the output of
the receiver is typically 125
Vp-p due to the 8:1 attenuation
from Ref In to Rcv Out. The reference noise can be reduced
by connecting an external capacitor between the Noise
Reduction pin and ground. For example, 0.1
F capacitor
reduces the high-frequency noise to about 200
Vp-p at the
output of the reference and about 25
Vp-p at the output of
the receiver.
Request Application Bulletin AB-014 for details of a
more complete protection circuit.
FIGURE 6. Protecting the Sense Resistors.
FIGURE 7. Optional Voltage Reference External Trim Circuit.
8
RCV420
FIGURE 8. RCV420 Used in Conjunction with XTR101 to Form a Complete Solution for 4-20mA Loop.
0.01F
Q
1
1N4148
12V
1F
5
4
2
3
15
13
14
11
10
12
1F
V
O
= 0 to 5V
RCV420
16
+12V
8
7
9
E
B
14
11
12
13
4
3
2
XTR105
R
CM
= 1k
1
0.01F
R
Z
137
R
LIN1
5760
R
G
402
RTD
Pt100
100C to
600C
6
R
G
R
G
V
IN
V
IN
+
V
LIN
I
R1
I
R2
V
REG
V+
I
RET
I
O
10
I
O
= 4mA 20mA
NOTE: A two-wire RTD connection is shown. For remotely
located RTDs, a three-wire RTD conection is recommended.
R
G
becomes 383
, R
LIN2
is 8060
. See Figure 3 and
Table I.
FIGURE 9. Isolated 4-20mA Instrument Loop (RTD shown).
5
4
2
3
15
13
14
11
10
12
RCV420
16
16
2
15
10
8
7
9
V
V
O
V+
0 5V
ISO122
1
+15V
0
15V
1F
1F
Isolated Power
from PWS740
0.01F
Q
1
1N4148
8
7
9
E
B
14
11
12
13
4
3
2
XTR105
R
CM
= 1k
1
0.01F
R
LIN1
R
G
R
LIN2
RTD
6
R
G
R
G
V
LIN
I
R1
I
R2
V
REG
V+
I
RET
I
O
10
I
O
= 4mA 20mA
V
IN
V
IN
+
R
Z
NOTE: A three-wire RTD connection is shown.
For a two-wire RTD connection eliminate R
LIN2
.
RCV420
9
1
2
3
15
14
V
RCV420
12
13
5
OPA237
O
20k
10
11
C
T
420mA
(50V)
+6.25V
12k
+10V
+6.25V
R
S
R
S
C
T
1
2
3
RCV420
In
+In
15
14
12
5
V
O
I
1
I
2
13
R
S
R
S
C
T
1
2
3
RCV420
In
+In
10
11
12
15
14
13
420mA
5
(1)
V
O
(05V)
R
S
R
S
C
T
1
2
3
RCV420
In
+In
10
11
12
15
14
13
5
(N)
V
O
(05V)
R
CM
(1)
R
G
(1)
FIGURE 10. Series 4-20mA Receivers.
FIGURE 13. Power Supply Current Monitor Circuit.
FIGURE 12. 4-20mA to 5-0V Conversion.
V
O
= 6.25V (0.3125) (I
IN
)
NOTE: (1) R
CM
and R
G
are used to provide a first order correction of CMR
and Gain Error, respectively. Table 1 gives typical resistor values for R
CM
and R
G
when as many as three RCV420s are stacked. Table II gives
typical CMR and Gain Error with no correction. Further improvement in
CMR and Gain Error can be achieved using a 500k
potentiometer for
R
CM
and a 100
potentiometer for R
G
.
RCV420
R
CM
(k
)
R
G
(
)
1
0
2
200
7
3
67
23
TABLE 1. Typical Values for R
CM
and R
G
.
TABLE II. Typical CMR and Gain Error
Without Correction.
RCV420
CMR (dB)
GAIN ERROR %
1
94
0.025
2
68
0.075
3
62
0.200
FIGURE 11. Differential Current-to-Voltage Converter.
V
O
= 0.3125 (I
1
I
2
)
Max Gain Error = 0.1% (RCV420BG)
(
I
L
MAX
16mA
1
)
NOTE: (1) R
X
= R
S
/
C
T
15
5
12
13
3
2
1
14
RCV420
+In
+In
Load
Load
Power
Supply
C
T
15
5
12
13
14
RCV420
In
I
L
+In
Power
Supply
40V (max)
+40V (max)
R
X
(1)
R
X
(1)
R
X
(1)
R
X
(1)
R
S
R
S
R
S
R
S
V
O
(0-5V)
V
O
(0-5V)
I
L
10
RCV420
301
301
0-20mA
Input
75
75
1
2
3
16
4
+15V
15V
100k
RCV420
13
1.01k
5
11.5k
92k
99k
300k
300k
10
11
14
15
12
V
O
0-5V
10.0V
Ref
1
2
12
15
14
10
11
75
75
300k
99k
10.0V
Reference
1.01k
RCV420
V
05V
OUT
13
5
16
4
15V
+15V
LM193
1.27k
10k
604
6.95V
Underrange
Output
Overrange
Output
1M
10k
10k
3
10.0V
10k
+15V
2N3904
22.9k
10k
0.57V
8
4
420mA
Input
+5V
AT&T
LH1191
Solid-State
Relay
555
Timer
8
4
3
1
2
5
1F
0.01F
1F
7
6
470
47k
92k
11.5k
300k
100k
FIGURE 14. 4-20mA Current Loop Receiver with Input Overload Protection.
See Application Bulletin AB-014 for more details.
FIGURE 15. 0-20mA/0-5V Receiver Using RCV420.
See Application Bulletin AB-018 for more details.
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