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[FAQ] ISOM8110: How do I design ISOM8110 to have the best timing performance for switching applications?

Andrew J
Mastermind 26845 points
Part Number: ISOM8110

Tool/software:

FAQ: Isolation >> Opto-Emulators >> Current FAQ

The ISOM8110 is designed for analog behavior. Switching performance is possible and depends on the circuit design. However, we need to pay attention to the test conditions to make sure the output transistor is in saturation mode (being used as a switch).

  • 0
    TI__Mastermind 26845 points

    If needed see What is Current Transfer Ratio (CTR) to start.

    • Saturation mode (when ISOM is acting as switch) is achieved when IF * CTR >>IC_max.
      • Saturation mode specs are shown in Ton, Toff, and Ts when the test condition starts with VCC=5V. 
      • You will notice two conditions are provided to show the device in saturation mode with a strong IF (16mA) and a weaker IF (1.6mA). The typical application curves usually use the 1.6mA test condition. 
    • The ISOM811x is in active mode (analog behavior) when IC_max > IF *CTR.
      • Active mode specs for tr, tf, Ton, Toff can be identified when the test condition starts with VCC=10V. 

     

    The red boxes are the non-saturated timings, and highlighted sections are the active mode characteristics. The data sheet shows saturated mode will have faster switching performance when compared to unsaturated (with the specs where IF = 16mA are even faster). 

    TON + TOFF together here is 19.4us which is slower than the saturated (at 1.6mA) TON + TOFF which is 15.3us. Therefore, the saturated performance is faster.