ISO255 Isolation amplifier IC circuit and iso255 pinout

internal block diagram with pin numbers according to datasheet by Burr-Brown®

ISO255 is isolation amplifier by Burr-Brown with some unique features enlisted below.

  • ISO255 have dedicated power port isolated from both input and output sides
  • ISO255 have built-in isolated DC-DC converter for input circuit and output circuit
  • ISO255 have syc feature to synchronize modulation frequencies of all ISO255 IC’s in circuit.
  • Gain can be adjusted by applying an external resistor between +Rg and -Rg pins.
  • input/output Signal Common pins are separate from power GND pins. May be combined externally.
  • Input is double line +Vin and -Vin.

Here is ISO255 example circuit which feeding a resistance bridge circuit output voltage for further measurement with being isolated from next circuitry.

ISO255 Bridge conditioning circuit example (image courtesy of Burr-Brown®)
ISO255 Pin configuration
(source is datasheet by Burr-Brown®)

+15V are applied on +Vs3 and GND3 pins. +Vs1,-Vs1 and +Vs2, -Vs2 are outputs of internal DC/DC converter. And filtered by 220nF capacitors. Output offset is adjusted by 200kΩ trimmer. In this example gain is unity due to +Rg and -Rg pins are open. Gain can be controlled by connecting +Rg and -Rg pins to a resistor. Gain may be calculated by following formula.

G = 1 + 50KΩ / Rg

ISO255 important parameters

  • Input voltage range is ±10V
  • Output voltage range is ±10V
  • Small signal bandwidth is up to 50KHz
  • Gain Error 0.15% at G=1
  • Input offset maximum ± (0.125 + 101/G)
  • Power supply voltage range : 11V~18V
  • Sync frequency range: 1MHz ~ 1.4MHz
  • Isolation leakage current: 2uA maximum @ 240V 50Hz
  • Isolation Mode Voltage IMV ,dV/dt: 20kV/uS
  • Isolation barrier impedance: 1014 Ω || 2pF
  • Isolation Voltage: 2500V
  • Available packages: 28 pin plastic DIP 0.6″ wide
  • Operating temperature range: -40°C ~ 85°C

Isolation Mode voltage is voltage between GND1 and GND2.

Other relevant IC

ISO124P isolation amplifier  ISO124U isolation amplifier  NJM41005-T Isolation Amplifier

AD215 isolation amplifier  AMC1200/B  ISO124U SI8920 ISO120  AD202  PS8551AL4-AX   ADUM4190   ADUM3190   AD204    AMC1301  NJM41005-T   AD215  AMC1300   AMC1302   AMC1200/B   ISO224  AMC1211A-Q1 AMC1301DWVR  MAX14850  ADuM6132  ADuM3150  HCPL-7800   ISO124, ISO122

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