1B22A Datasheet

Programmable, ISOlated Voltage-to-current Converter


Features, Applications

FEATURES Internal Isolated Loop Supply Drives 1000 Load Pin Programmable Inputs: +10 V Pin Programmable Outputs: 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% High CMR: 90 dB min Small Package: 2.10" 0.35" Meets IEEE STD 472: CMV Transient Protection (SWC) APPLICATIONS Multichannel Process Control D/A Converter--Current Loop Interface Analog Transmitters and Controllers Remote Data Acquisition Systems GENERAL DESCRIPTION


The 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. 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 programmable for +10 V inputs and 20 mA outputs using an internal resistor network. It can also be set by an external resistor to accept +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. 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 it is sufficient to drive a 1000 load. The 1B22 is fully specified over to +85�C and operates over the industrial to +85�C) temperature range.

Isolated Loop Power: Internal loop supply completely isolates the loop from the input terminals (1500 V rms) and provides the capability to drive to 1000 loads. This eliminates the need for an external dc/dc converter. Ease of Use: The 1B22 offers complete isolated voltage-tocurrent 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 1500 V rms and meets the IEEE Standard for Common-Mode Voltage Transient Protection (STD 472-SWC). Small Size: The 1B22 package size � 2.1" DIP) makes it an excellent choice in multichannel systems for maximum channel density. The 0.35" height also facilitates applications with limited board clearance.

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 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 � Analog Devices, Inc., 2000

Model INPUT SPECIFICATIONS Factory Calibrated, User Selectable Input Impedance +10 V Input Range +5 V Input Range OUTPUT SPECIFICATIONS Current Output Range, User Selectable Load Compliance Range, VLOOP +15 V Load Compliance Range, VLOOP +28 V Maximum Output Current @ Input Overload Output Noise, 100 Hz Bandwidth NONLINEARITY of Span) ISOLATION CMV, Input to Output Continuous CMR, 60 Hz Normal-Mode Output Protection CMV Transient Protection ACCURACY Warm-Up Time to Rated Performance Total Output Error @ +25�C Offset (VIN 0 V) Span (VIN +10 V) vs. Temperature to +85�C) Offset Span DYNAMIC RESPONSE Settling Time of FS for 10 V Step Small Signal Bandwidth POWER SUPPLY Bipolar Input Supplies Operating Voltage Quiescent Current Power Supply Rejection Loop Supply Operating Voltage Operating Current, at Full-Scale Output Loop Supply Rejection ENVIRONMENTAL Temperature Range Rated Performance Operating Storage Relative Humidity, Noncondensing CASE SIZE

to 20 mA, 8 V min 20 V min 300 nA p-p 0.02% 0.05% max) 1500 V rms max 90 dB min 240 V rms Continuous IEEE-STD 472 (SWC) 5 min � 0.7% Full Scale � 300 nA/�C � 50 ppm/�C 400 Hz


The 1B22 produces an isolated 20 mA output 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 network to provide pin-strappable input ranges +5 V and +10 V and output ranges 20 mA and 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 V is used to develop 4 mA offset for the 20 mA current loop output.

After passing through signal transformer T1, the amplitude modulated signal is demodulated and filtered by a single pole filter. This filtered output is the control signal for the voltageto-current converter stage. Timing information for the demodulator is derived from the power transformer T2. The 1B22 outputs are protected from accidental shorts to ac line voltages 240 V rms. Combined with 1500 V input to output isolation, the 1B22 provides unbeatable protection against transients, wiring errors and current loop short circuits to power lines. The dc-dc converter consists of a power driver, power transformer T2, a full wave rectifier and a filter. The dc-dc converter provides the power for the output circuitry as well as the isolated compliance voltage for the loop. This voltage is proportional to VLOOP on the input side. The 1B22 requires 15 V supplies to power the input side circuitry and +30 V supply for the dc-dc converter.

Optional Trim Adjustments: Figure is an example of using potentiometers for trimming gain and offset for +10 V input and 20 mA output. The network for offset adjustment keeps the resistors relatively small to minimize noise effects while giving a sensitivity 1% of span. The value of R1 should 5 M for the +10 V range (for +5 V configurations, 1.2 M resistor should be used). For more adjustment range, resistors smaller than 274 k can be used.

Basic Interconnections: The 1B22 may be applied to achieve rated performance as shown in Figure 2. For 10 V signals either or IN2 can be used for input; for +5 V signals jumper to IN2. Similarly, for 20 mA operation the 4 mA OFFSET node should be jumpered to the S. NODE, while for mA it should be tied to COM. Figure 3 shows 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 V to VLOOP (Pin 24) and COM to P.COM (Pin 25). For additional compliance voltage, P.COM can be connected V to drive higher loads.



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Manufacturer information


Analog Devices, Inc. Introduction - Analog Devices, Inc. (NASDAQ: ADI) defines innovation and excellence in signal processing. ADI's analog, mixed-signal, and digital signal processing (DSP) integrated circuits (IC) play a fundamental role in converting, conditioning, and processing real-world phenomena such as light, sound, temperature, motion, and pressure into electrical signals to be used in a wide array of electronic equipment. ADI is synonymous with high performance among electronics manufacturers and we collaborate with our customers to define the very best in the quality of the user experience. That means the clearest image, crispest sound, and optimum interface, size and performance in thousands of entertainment, medical, communications, industrial and other applications.

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