AD693 Loop-Powered 4-20 mA Sensor Transmitter

The AD693 is a monolithic signal conditioning circuit which accepts low-level inputs from a variety of transducers to control a standard 4-20 mA, two-wire current loop. An on-chip voltage reference and auxiliary amplifier are provided for transducer excitation; up to 3.5 mA of excitation current is available when the device is operated in the loop-powered mode. Alternatively, the device may be locally powered for three-wire applications when 0-20 mA operation is desired.

Precalibrated 30 mV and 60 mV input spans may be set by simple pin strapping. Other spans from 1 mV to 100 mV may be realized with the addition of external resistors. The auxiliary amplifier may be used in combination with on-chip voltages to provide six precalibrated ranges for 100 (ohm) RTDs. Output span and zero are also determined by pin strapping to obtain the standard ranges: 4-20mA, 12 ± 8 mA and 0-20 mA.

Active laser trimming of the AD693's thin-film resistors result in high levels of accuracy without the need for additional adjustments and calibration. Total unadjusted error is tested on every device to be less than 0.5% of full scale at +25°C, and less than 0.75% over the industrial temperature range. Residual nonlinearity is under 0.05%. The AD693 also allows for the use of an external pass transistor to further reduce errors caused by self-heating.

For transmission of low-level signals from RTDs, bridges and pressure transducers, the AD693 offers a cost-effective signal conditioning solution. It is recommended as a replacement for discrete designs in a variety of applications in process control, factory automation and system monitoring.

The AD693 is packaged in a 20-pin ceramic side-brazed DIP, 20-pin Cerdip, and 20-pin LCCC and is specified over the -40°C to +85°C industrial temperature range.

Features and Benefits
  • Instrumentation Amplifier Front End
  • Loop-Powered Operation
  • Independently Adjustable Output Span and Zero
  • Precalibrated Output Spans:
    4-12 mA Unipolar
    0-20 mA Unipolar
    12 ± 8mA Bipolar
  • Precalibrated 20 mV or 60mV Input Spans
  • Precalibrated 100 O RTD Interface
  • 6.2 V Reference with Up to 3.5 mA of Current Available
  • Uncommitted Auxiliary Amp for Extra Flexibility
  • Optional External Pass Transistor to Reduce Self-Heating Errors
  • Interface & Isolation
    Data Sheets
    AD693: Loop-Powered 4-20 mA Sensor Transmitter Data Sheet (Rev. A)PDF 496 kB
    Application Notes
    AN-275: Versatile Transmitter Chip Links Strain Gauges and RTDs to Current LoopPDF 948 kB
    Technical Books
    Order Information
    Part NumberPackagePacking QtyTemp RangePrice 100-499Price 1000+RoHS
    AD693AD Production20 ld Side-Brazed CerDipOTH 19-40 to 85C25.723.19N
    AD693AE Production20 ld LCCOTH 54-40 to 85C26.8724.25Y
    AD693AQ Production20 ld CerDIPOTH 18-40 to 85C10.79.28N
    Reference Materials
    AD693: Loop-Powered 4-20 mA Sensor Transmitter Data Sheet (Rev. A) ad693
    AN-275: Versatile Transmitter Chip Links Strain Gauges and RTDs to Current Loop ad693
    Auto-Zero Amplifiers ad693