ISO1212: What is the difference between ISO1212 and ISO1211 when applied to AC input?

Part Number: ISO1212
Other Parts Discussed in Thread: ISO1211

Hi team,

What is the difference between ISO1212 and ISO1211 when applied to AC input? which one is better?

Could you share ISO1212 reference schematic when applied to AC input. thanks 

  • Hi Jimmy:

    Thanks for posting your question on E2E!

    Either approach doesn't have an advantage over the other functionally. However, one key consideration that the system designer has to take into account when using the bridge rectification is the forward and reverse breakdown of the diodes. 2x diode forward voltages should be added when calculating the input thresholds due to the two diode drops in the path. Also, the reverse breakdown of the diodes should be higher than the peak AC input voltage. These considerations don't apply when using the ISO1212 for AC inputs. 

    Input thresholds can be estimated using this calculator.

    The schematics shown in the datasheet is complete and show the full implementation details. We don't have the reference schematics in other formats.

    Regards,

    Dushmantha

  • Hi team,

    But if use ISO1212 size will bigger than photocoupler, my customer ac input data rate around 500K. 

    Q1: Can use ISO2111 when the data rate 500K?

    Q2: If use ISO1212 how to define  Rthr and Cin ?

  • Hi Jimmy:

    ISO1211 and ISO1212 devices are capable of running up to 4 Mbps, so I don't see any concerns in running at 500 kbps.

    Please use the threshold calculator to estimate the Rthr value first (or refer to section 9.2.1.2 of the datasheet). Rthr together with Cin will create a RC low pass filter at ISO1212 input. Cin should be chosen such that the RC filter would filter out any unwanted noise at the input of ISO1212 while having enough bandwidth to pass the 500 kbps data. When Cin is used with the bridge rectification, Cin should be large enough to filter out any ripple at the input signal after going through the rectification.

    You also find this tech note useful when designing for AC input signals.

    Regards,

    Dushmantha

  • Hi Jimmy:

    I'm hoping that I was able to answer all your questions.

    Please let me know if you have any further questions by replying to this thread or clicking on Ask a related question button.

    Regards,

    Dushmantha