SLLA284G July   2022  – September 2023 ISO5451 , ISO5452 , ISO5851 , ISO5852S , ISO7142CC , ISO7142CC-Q1 , ISO721 , ISO721-Q1 , ISO721M , ISO721M-EP , ISO722 , ISO7220A , ISO7220M , ISO7221A , ISO7221B , ISO7221C , ISO7221M , ISO722M , ISO7230C , ISO7230M , ISO7231C , ISO7231M , ISO7240C , ISO7240CF , ISO7240M , ISO7241C , ISO7241M , ISO7242C , ISO7242M , ISO7310-Q1 , ISO7310C , ISO7340-Q1 , ISO7340C , ISO7340FC , ISO7341-Q1 , ISO7341C , ISO7341FC , ISO7342-Q1 , ISO7342C , ISO7342FC , ISO7740 , ISO7741 , ISO7742 , ISO7760 , ISO7761 , ISO7762 , ISO7810 , ISO7820 , ISO7821 , ISO7830 , ISO7831 , ISO7840 , ISO7841 , ISO7842

 

  1.   1
  2.   Digital Isolator Design Guide
  3.   Trademarks
  4. 1Operating Principle
    1. 1.1 Edge-Based Communication
    2. 1.2 On-Off Keying (OOK) Based Communication
  5. 2Typical Applications for Digital Isolators and Isolated Functions
  6. 3Digital Isolator Selection Guide
    1. 3.1 Parameters of Interest
    2. 3.2 Isolator Families
  7. 4PCB Design Guidelines
    1. 4.1 PCB Material
    2. 4.2 Layer Stack
    3. 4.3 Creepage Distance
    4. 4.4 Controlled Impedance Transmission Lines
    5. 4.5 Reference Planes
    6. 4.6 Routing
    7. 4.7 Vias
    8. 4.8 Decoupling Capacitors
  8. 5Summary
  9. 6References
  10. 7Revision History

3.1 Parameters of Interest

This section briefly describes some of the parameters that are present in a typical isolator datasheet and their relevance to system design.

Isolation Performance:

  1. Maximum transient isolation voltage (VIOTM) and isolation withstand voltage (VISO) indicate an isolator’s ability to withstand temporary (less than 60 seconds) high voltage.
  2. Maximum repetitive peak voltage (VIORM) and working voltage (VIOWM) indicate the continuous voltage that the isolator can withstand throughout its lifetime.
  3. Maximum surge isolation voltage (VIOSM) indicates the maximum impulse voltage (waveform with 1.2-µs rise and 50-µs decay time) that the isolator can withstand.

Timing Parameters:

  1. Data rate.
  2. Propagation delay is important in systems where the round trip delay adds to the timing budget (for example, SPI interface) or if the delay is part of a control loop.
  3. Propagation delay skew is important if timing budget relies on matching between channels; for example, if clock is transmitted on one channel and data on another channel in the same direction.
  4. Glitch filter: Some digital isolators come with an integrated glitch filter that helps them operate well, even in noisy environments. However, the glitch filter increases propagation delay and reduces data rate.

Common Mode Transient Immunity (CMTI):

CMTI indicates the isolator’s ability to tolerate fast changes in the potential difference between its grounds, or in other words, fast changes in common mode, without causing bit errors. High CMTI indicates a robust isolation channel.

Power Consumption:

Power consumption per channel at data rate of interest.

Package:

  1. Creepage and Clearance: Distance along the surface of the package and through the air between pins on one side of the isolator to the pins on the other side. System level standards mandate minimum values of these parameters based on the working voltage, the peak transient voltage, and the surge voltage.
  2. Comparative Tracking Index (CTI) indicates the ability of the package mold compound to handle steady high voltage without surface degradation. A higher CTI allows the use of smaller packages for the same working voltage.