SNLA490 March   2025 ISOM8110-Q1 , ISOM8111-Q1 , ISOM8112-Q1 , ISOM8113-Q1 , ISOM8115-Q1 , ISOM8116-Q1 , ISOM8117-Q1 , ISOM8118-Q1

 

  1.   1
  2.   Summary
  3. 1Relay Contact Sticking in OBCs
    1. 1.1 Relays Used in OBCs
    2. 1.2 Causes and Hazards of Relay Contact Sticking
  4. 2About Opto-emulators
    1. 2.1 Introduction to ISOM811x-Q1 and Key Parameters Like CTR
    2. 2.2 Performance Comparison with Optocoupler and Single-Channel Digital Isolator
  5. 3AC Relay Weld Detection in V2L Circuit for OBCs Based on ISOM8118-Q1
    1. 3.1 What Is V2L for OBCs
    2. 3.2 Design Reference for AC Relay Weld Detection Circuit in V2L
    3. 3.3 Design Examples and Selection Guidelines Based on Typical Circuits
      1. 3.3.1 Select Voltage Judgment Threshold VTH and IFmin
      2. 3.3.2 Select Current-limiting Resistor R1
      3. 3.3.3 Select the pull-up resistor R2
  6. 4Summary
  7. 5References

2.1 Introduction to ISOM811x-Q1 and Key Parameters Like CTR

The ISOM811x-Q1 family of devices are TI’s opto-emulators with emulated LED input and transistor output. This family is compatible with a variety of traditional optocoupler packages and supports pin-to-pin upgrades. The ISOM811x-Q1 uses an emulated LED as the input stage, with a silicon dioxide (SiO2)-based isolation barrier between the input and output, effectively inhibiting signal transmission degradation found in traditional optocoupler technologies.

The current transfer ratio (CTR) is an important parameter for opto-emulators, defined as:

Equation 1. C T R % = I C I F × 100 %

Where IC is the collector current through the output stage and IF is the forward current through the input stage. At the same minimum input current IFmin, a higher CTR could lead to a more saturated secondary “transistor” and a smaller conduction voltage drop. The ISOM811x-Q1 family offers several CTR options from 100% to 560%. Due to the stability of the SiO2-based isolation barrier, this key metric is stable across the full temperature range and full input current IF range, facilitating designers to design boundary conditions based on actual input.

Input IF and Output IC of the Opto-emulatorFigure 2-1 Input IF and Output IC of the Opto-emulator