a Programmable, Isolated

Voltage-to-Current Converter
1B22
FEATURES FUNCTIONAL BLOCK DIAGRAM
Internal Isolated Loop Supply Drives 1000 ⍀ Load
Pin Programmable Inputs: 0 V to +5 V or 0 V to +10 V
IN1
Pin Programmable Outputs: 4 to 20 mA or 0 to 20 mA 1B22 OUT
IN2 REF HI
High CMV Isolation: 1500 V RMS 4mA
RESISTOR
NETWORK
SIGNAL
ISOLATION
Normal-Mode Output Protection: 240 V RMS OFFSET
OUT
S. NODE LO
High Accuracy MODULATOR DEMODULATOR
Low Offset Tempco: ⴞ300 nA/ⴗC PROT

Low Gain Tempco: ⴞ50 ppm/ⴗC SYNC

POWER
ISOLATION
Low Nonlinearity: ⴞ0.02% +15V
RECTIFIER/
High CMR: 90 dB min –15V OSCILLATOR LOOP SUPPLY
Small Package: 1.0" ⴛ 2.10" ⴛ 0.35" A. COM

Meets IEEE STD 472: CMV Transient Protection (SWC)

P. COM VLOOP

APPLICATIONS
Multichannel Process Control
D/A Converter—Current Loop Interface
Analog Transmitters and Controllers DESIGN FEATURES AND USER BENEFITS
Remote Data Acquisition Systems Isolated Loop Power: Internal loop supply completely
isolates the loop from the input terminals (1500 V rms) and
GENERAL DESCRIPTION provides the capability to drive 0 Ω to 1000 Ω loads. This elimi-
The 1B22 is an isolated voltage-to-current converter that nates the need for an external dc/dc converter.
incorporates transformer isolation to achieve high performance Ease of Use: The 1B22 offers complete isolated voltage-to-
and automated surface mount manufacturing for low cost current conversion with minimum external parts required to get
and increased reliability. Designed for industrial applications, a conditioned current signal. No external buffers or drivers are
it is especially suited for harsh environments with extremely required.
high common-mode interference. With programmable inputs
High CMV Isolation: The 1B22 features high input to output
and outputs, the 1B22 provides an unbeatable combination of
galvanic isolation to eliminate ground loops and offer protection
versatility and performance in a compact plastic package.
against damage from transients and fault voltages. The isolation
Functionally, the V/I converter consists of four basic sections: barrier will withstand continuous CMV of 1500 V rms and meets
input conditioning, modulator/demodulator, isolated loop the IEEE Standard for Common-Mode Voltage Transient Pro-
supply and current source (Figure 1). The 1B22 is pin program- tection (STD 472-SWC).
mable for 0 V to +5 V or 0 V to +10 V inputs and 0 to 20 mA
Small Size: The 1B22 package size (1.0" × 2.1" DIP) makes it
or 4 to 20 mA outputs using an internal resistor network. It can
an excellent choice in multichannel systems for maximum chan-
also be set by an external resistor to accept 0 V to +1 V to 0 V
nel density. The 0.35" height also facilitates applications with
to +10 V inputs. Transformer coupling provides 1500 V rms
limited board clearance.
galvanic isolation between the inputs and the current loop.
Nonlinearity is an excellent ± 0.05% max.
Loop power is generated internally through a dc/dc converter
and is also isolated from the input side (1500 V rms). Loop
compliance voltage is dependent on the voltage supplied to the
1B22, and with VLOOP = 28 V, it is sufficient to drive a 1000 Ω
load.
The 1B22 is fully specified over –25°C to +85°C and operates
over the industrial (–40°C to +85°C) temperature range.

REV. B
Information furnished by Analog Devices is believed to be accurate and
reliable. However, no responsibility is assumed by Analog Devices for its
use, nor for any infringements of patents or other rights of third parties One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
which may result from its use. No license is granted by implication or Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
otherwise under any patent or patent rights of Analog Devices. Fax: 781/326-8703 © Analog Devices, Inc., 2000
1B22–SPECIFICATIONS (typical @ +25ⴗC and V = ⴞ15 V, V S LOOP = +24 V, unless otherwise noted)
Model 1B22AN
OUTLINE DIMENSIONS
INPUT SPECIFICATIONS Dimensions shown in inches and (mm).
Factory Calibrated, User Selectable 0 V to +5 V, 0 V to +10 V
Input Impedance
0 V to +10 V Input Range 50 kΩ
0 V to +5 V Input Range 25 kΩ
OUTPUT SPECIFICATIONS
Current Output Range, User Selectable 4 to 20 mA, 0 to 20 mA
Load Compliance Range, VLOOP = +15 V 8 V min
Load Compliance Range, VLOOP = +28 V 20 V min
Maximum Output Current @ Input Overload 30 mA
Output Noise, 100 Hz Bandwidth 300 nA p-p
NONLINEARITY (% of Span) ± 0.02% (± 0.05% max)
ISOLATION
CMV, Input to Output Continuous 1500 V rms max
CMR, @ 60 Hz 90 dB min
Normal-Mode Output Protection 240 V rms Continuous
CMV Transient Protection IEEE-STD 472 (SWC)
ACCURACY
Warm-Up Time to Rated Performance 5 min
Total Output Error @ +25°C
Offset (VIN = 0 V) ± 60 µA
Span (VIN = +10 V) ± 0.7% Full Scale
vs. Temperature (–25°C to +85°C)
Offset ± 300 nA/°C AC1225 MATING SOCKET
Span ± 50 ppm/°C
DYNAMIC RESPONSE
Settling Time to 0.1% of FS for 10 V Step 9 ms
Small Signal Bandwidth 400 Hz
POWER SUPPLY
Bipolar Input Supplies
Operating Voltage ± 15 V ± 5%
Quiescent Current ± 7.5 mA
Power Supply Rejection ± 0.01%/V
Loop Supply
Operating Voltage +14 V to +30 V
Operating Current, at Full-Scale Output 25 mA PIN DESIGNATIONS
Loop Supply Rejection ± 0.005%/V
Pin Function
ENVIRONMENTAL
Temperature Range 11 OUT HI
Rated Performance –25°C to +85°C 16 IN2
Operating –40°C to +85°C
17 IN1
Storage –40°C to +85°C
Relative Humidity, Noncondensing 0 to 95% @ 60°C 18 S. NODE
19 4 mA OFFSET
CASE SIZE 1.0" × 2.1" × 0.35"
20 +15 V
Specifications subject to change without notice. 21 ANA COM
22 –15 V
23 SYNC
24 VLOOP
25 POWER COM
38 OUT LO

–2– REV. B
 1B22
INSIDE THE 1B22
The 1B22 produces an isolated 4 to 20 mA or 0 to 20 mA out-
put current which is proportional to the input voltage and
independent of the output load resistance (Figure 1). The input
stage is configured as an inverting amplifier with a resistor net-
work to provide pin-strappable input ranges of 0 V to +5 V and
0 V to +10 V and output ranges of 0 to 20 mA and 4 to 20 mA.
The conditioned signal is modulated to generate a square wave
that drives transformer T1. The peak-to-peak amplitude of the
signal is proportional to VIN. An internal, high stability reference
with a nominal output voltage of +6.4 V is used to develop a
4 mA offset for the 4 to 20 mA current loop output.
Figure 2. Basic Interconnections

Figure 1. 1B22 Functional Block Diagram

After passing through signal transformer T1, the amplitude
modulated signal is demodulated and filtered by a single pole Figure 3. Internal Resistor Network
filter. This filtered output is the control signal for the voltage- Optional Trim Adjustments: Figure 4 is an example of using
to-current converter stage. Timing information for the potentiometers for trimming gain and offset for a 0 V to +10 V
demodulator is derived from the power transformer T2. The input and 4 to 20 mA output. The network for offset adjustment
1B22 outputs are protected from accidental shorts to ac line keeps the resistors relatively small to minimize noise effects
voltages up to 240 V rms. Combined with 1500 V input to out- while giving a sensitivity of ± 1% of span. The value of R1
put isolation, the 1B22 provides unbeatable protection against should be 5 MΩ for the 0 V to +10 V range (for 0 V to +5 V
transients, wiring errors and current loop short circuits to power configurations, a 1.2 MΩ resistor should be used). For more
lines. adjustment range, resistors smaller than 274 kΩ can be used.
The dc-dc converter consists of a power driver, power trans-
former T2, a full wave rectifier and a filter. The dc-dc converter IN1
1B22 OUT
provides the power for the output circuitry as well as the VIN
1k⍀ IN2
HI
50k⍀
isolated compliance voltage for the loop. This voltage is propor- 4mA RESISTOR OUT
R1 REF
tional to VLOOP on the input side. The 1B22 requires ± 15 V OFF NETWORK
PROT
LO

supplies to power the input side circuitry and a +14 V to +30 V +15V 20k⍀ S. NODE
supply for the dc-dc converter. 274k⍀
50k⍀ SYNC
1k⍀ +15V
USING THE 1B22 –15V
RECTIFIER/
COM POWER
Basic Interconnections: The 1B22 may be applied to achieve DRIVER LOOP
SUPPLY
rated performance as shown in Figure 2. For 0 V to 10 V signals –15V

either IN1 or IN2 can be used for input; for 0 V to +5 V signals

jumper IN1 to IN2. Similarly, for 4 to 20 mA operation the VLOOP P. COM
4 mA OFFSET node should be jumpered to the S. NODE,
while for 0 to 20 mA it should be tied to COM. Figure 3 shows Figure 4. Optional Offset and Span Adjustment
the functional diagram of the resistor network used in the 1B22.
For applications where a separate loop supply is not available,
the ± 15 V supplies can be used by connecting +15 V to VLOOP
(Pin 24) and COM to P.COM (Pin 25). For additional compli-
ance voltage, P.COM can be connected to –15 V to drive higher
loads.

REV. B –3–
1B22
Synchronizing Multiple 1B22s: In applications where mul- APPLICATIONS
tiple 1B22s are used in close proximity, radiated individual Isolated D/A Converter: The 1B22 offers total ground isola-
oscillator frequencies may cause “beat frequency” related out- tion and protection from high voltage transients in interfacing
put errors. These errors can be eliminated by driving the SYNC D/A converters to standard 4 to 20 mA current loops. The D/A
pins of all the units with a 40 kHz clock circuit at 50% duty converter, such as the Analog Devices’ 12-bit AD7245
cycle (Figure 5). The SYNC input typically has an input imped- DACPORT®, should be connected for operation on the unipo-
ance of 150 kΩ储180 pF. lar 0 V to +10 V output range. This is shown in Figure 7.

C1193a–2.2–3/00 (rev. B)
Figure 5. Multiple 1B22s’ Synchronization Figure 7. D/A Converter–Isolated 4-20 mA Interface
Loop Supply Requirements: The 1B22 design allows flexible Pressure Transmitter: In Figure 8, the 1B22 is used in a
loop supply options. The loop supply voltage required for any pressure transmitter application to provide complete input-
value of load resistance can be calculated from the following output isolation and avoid signal errors due to ground loop cur-
equation: rents. The process pressure is monitored with a strain gage type
pressure transducer interfaced by the Analog Devices’ 1B32
2RL + 780
VLOOP = transducer signal conditioner. The high level voltage output of
106 the 1B32 is converted to the isolated 4 to 20 mA current for
This value allows for approximately 10% overrange capability. transmission to a remote recorder or indicator.
The graph in Figure 6 shows the relationship between supply
voltage and load resistance.

Figure 8. Isolated Pressure Transmitter

PRINTED IN U.S.A.

Figure 6. Loop Supply vs. Load

DACPORT is a registered trademark of Analog Devices, Inc.

–4– REV. B
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