Programmable, Isolated
Voltage-to-Current Converter
a
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
Pin Programmable Outputs: 4 to 20 mA or 0 to 20 mA
High CMV Isolation: 1500 V RMS
Normal-Mode Output Protection: 240 V RMS
High Accuracy
Low Offset Tempco: ؎300 nA/؇C
Low Gain Tempco: ؎50 ppm/؇C
Low Nonlinearity: ؎0.02%
IN1
1B22
OUT
IN2
REF
HI
RESISTOR
NETWORK
SIGNAL
4mA
ISOLATION
OFFSET
OUT
LO
S. NODE
MODULATOR
DEMODULATOR
PROT
POWER
ISOLATION
SYNC
+15V
RECTIFIER/
LOOP SUPPLY
OSCILLATOR
–15V
High CMR: 90 dB min
Small Package: 1.0" ؋
2.10" ؋
0.35"
Meets IEEE STD 472: CMV Transient Protection (SWC)
A. COM
V
P. COM
LOOP
APPLICATIONS
Multichannel Process Control
D/A Converter—Current Loop Interface
Analog Transmitters and Controllers
Remote Data Acquisition Systems
DESIGN FEATURES AND USER BENEFITS
Isolated Loop Power: Internal loop supply completely
isolates the loop from the input terminals (1500 V rms) and
provides the capability to drive 0 Ω to 1000 Ω loads. This elimi-
nates the need for an external dc/dc converter.
GENERAL DESCRIPTION
The 1B22 is an isolated voltage-to-current converter that
incorporates transformer isolation to achieve high performance
and automated surface mount manufacturing for low cost
and increased reliability. Designed for industrial applications,
it is especially suited for harsh environments with extremely
high common-mode interference. With programmable inputs
and outputs, the 1B22 provides an unbeatable combination of
versatility and performance in a compact plastic package.
Ease of Use: The 1B22 offers complete isolated voltage-to-
current conversion with minimum external parts required to get
a conditioned current signal. No external buffers or drivers are
required.
High CMV Isolation: The 1B22 features high input to output
galvanic isolation to eliminate ground loops and offer protection
against damage from transients and fault voltages. The isolation
barrier will withstand continuous CMV of 1500 V rms and meets
the IEEE Standard for Common-Mode Voltage Transient Pro-
tection (STD 472-SWC).
Functionally, the V/I converter consists of four basic sections:
input conditioning, modulator/demodulator, isolated loop
supply and current source (Figure 1). The 1B22 is pin program-
mable for 0 V to +5 V or 0 V to +10 V inputs and 0 to 20 mA
or 4 to 20 mA outputs using an internal resistor network. It can
also be set by an external resistor to accept 0 V to +1 V to 0 V
to +10 V inputs. Transformer coupling provides 1500 V rms
galvanic isolation between the inputs and the current loop.
Nonlinearity is an excellent 0.05% max.
Small Size: The 1B22 package size (1.0" × 2.1" DIP) makes it
an excellent choice in multichannel systems for maximum chan-
nel density. The 0.35" height also facilitates applications with
limited board clearance.
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 2000
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