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

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 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