Optically Coupled 20 mA Current Loop Transmitter

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The HCPL-4100 isolated 20 mA currrent loop transmitter is designed to operate as a transmitter in equipment using the 20 mA current loop. 20 mA current loop systems conventionally signal a logic high state by transmitting 20 mA of loop current (MARK), and signal a logic low state by allowing no more than a few milliamperes of loop current (SPACE).

Optical coupling of the signal from the logic input to the 20 mA current loop breaks ground loops and provides very high immunity to common mode interference.

The  data input is compatible with LSTTL, TTL, or CMOS logic gates. The input integrated circuit drives a GaAsP LED. The light emitted by the LED is sensed by a second integrated circuit that allows 20 mA to pass with a voltage drop of less than 2.7 volts when no light is emitted and allows less than 2 mA to pass when light is emitted. The transmitter output is capable of withstanding 27 volts. The input integrated circuit provides a controlled amount of LED drive current and takes into account any LED light output degradation. The internal shield allows a guaranteed 1000 V/ms common mode transient immunity.




  • Guaranteed 20 mA Loop Parameters
  • Data Input Compatible with LSTTL, TTL and CMOS Logic 
  • Internal Shield for High Common Mode Rejection
  • 20 kBaud Data Rate at 400 Metres Line Length
  • Guaranteed On and Off Output Current Levels
  • Safety Approval:
    UL Recognized - 3750 Vrms for 1 Minute
    CSA Approved
  • Optically Coupled 20 mA Current Loop Receiver, HCPL-4200, Also Available
  • Options available are:
    • 300 = Gull Wing Surface Mount Lead Option
    • 500 = Tape/Reel Packaging Option (1 K min.)
    • XXXE = Lead Free Option


  • Isolated 20 mA Current
  • Loop Transmitter in:
    Computer Peripherals
    Industrial Control Equipment
    Data Communications Equipment

Lifecycle Status



  • RoHS
    Pb & Pb-free options available

Lifecycle Status


Substance Compliance

  • RoHS
    Pb & Pb-free options available
Specification Value
Lifecycle Active
Distrib. Inventory Yes
Samples Available Yes
CMR (min.) (V/µs) 1000.0
Vcm (V) 50.0
RoHS6 Compliant Pb & Pb-free options available
Max Qty of Samples 20
Package 300mil DIP
Product Type 20 mA Current Loop Transmitter
Prop Delay (tPHL) Max. (µs) 1.6
Prop Delay tPHL Uom µs
Prop Delay (tPLH) Max. (µs) 1.6
Prop Delay tPLH Uom µs
VDD2 (V) 5.0
Prop Delay (tPHL) Max. (µs) 1.6 µs
Prop Delay (tPLH) Max. (µs) 1.6 µs


Application Brief (1) i
Application Note (5) i
Brochures (2) i
Data Sheet (1) i
Design Guide (1) i
FAQs (1) i
Obsolescence Notice (1) i
Options Data Sheet (5) i
Product Change Notice (PCN) (17) i
Regulatory Certificate (2) i
Selection Guide (2) i
White Papers (3) i