GENERAL DESCRIPTION
The 1B21 is an isolated voltage-to-current converter that incorporates a unique circuit design utilizing transformer-based isolation and automated surface-mount manufacturing technology. It provides an unbeatable combination of versatility and perfor-mance in a compact plastic package. Designed for industrial applications, it is especially suited for harsh environments with extremely high common-mode interference.
Functionally, the V/I converter consists of four basic sections: input conditioning, modulator, demodulator and current source (see Figure 1). The input is a resistor-programmable gain stage that accepts a 0 V to 1 V up to 0 V to 10 V voltage input. This maps into a 0 mA to 20 mA output or can be offset by 20% using the internal reference for 4 mA to 20 mA operation. The high level signal is modulated and passed across the barrier which provides complete input to output galvanic isolation of 1500 V rms continuous by the use of transformer-coupling techniques. Nonlinearity is an excellent ±0.05% maximum.
Designed for multichannel applications, the 1B21 requires an external loop supply and can accept up to 30 V maximum. This
provides a loop supply compliance of 27V, which is sufficient to drive a 1.35 kΩ load resistance.
The 1B21 is fully specified over −25°C to +85°C and operates over the industrial (−40°C to +85°C) temperature range.
DESIGN FEATURES AND USER BENEFITS
High CMV Isolation. The 1B21 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 1500V rms and meets the IEEE Standard for Transient Voltage Protection (Std. 472-SWC).
Small Size. The 1B21 package size (0.7” × 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.
Ease of Use. Complete isolated voltage-to-current conversion with minimum external parts required to get a conditioned current signal. No external buffers or drivers are required.

FEATURES
Wide input range: 0 V to 1 V up to 0 V to 10 V
High CMV isolation: 1500 V rms
Programmable output ranges: 4mA to 20mA
0 to 20 mA
Load resistance range: 0 to 1.35 kΩ maximum
High accuracy
Low offset tempco: ±300 nA/°C
Low gain tempco: ±50 ppm/°C
Low nonlinearity: ±0.02%
High CMR: 90 dB minimum
Small package: 0.7” × 2.1” × 0.35”
Meets IEEE Standard 472: transient protection (SWC)

APPLICATIONS
Multichannel process control
DAC—current loop interface
Analog transmitters and controllers
Remote data acquisition systems