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TINA/Spice/AMC1211-Q1: AMC1211-Q1:

Part Number: AMC1211-Q1
Other Parts Discussed in Thread: TINA-TI, , ISO224, AMC1300, AMC1302

Tool/software: TINA-TI or Spice Models

The Input of AMC1211-Q1 is on module 1.  The output of AMC1211-Q1 is on module 2.  If Vdd1 is lost while Vdd2 is powered, what is the differential output level?  I want the output to be zero.  Currently I use ACPL-C78A.  The output is 5V when Vdd1 is lost, which causes a lot of problems.  I hope TI does not have this drawback.


  • Hello Sam,

    Thanks for your post!

    The behavior of the device can be seen in section 7.3.3. Fail-Safe Output of the datasheet:

    "Figure 44 shows the fail-safe output of the AMC1211A-Q1 that is a negative differential output voltage that does
    not occur under normal device operation. As a reference value for the fail-safe detection on a system level, use
    the VFAILSAFE voltage as specified in the Electrical Characteristics table. "

    Typical VFAILSAFE voltage is -2.6V and the max is -2.5V.
  • Thank you very much for your reply.  the following stage is a single supply, differential amplifier.  So when Vdd1 is missing the output of the following stage should be saturated to zero.  This is safe.  If my understanding is correct, I can use the device.

    Please recommend me an isolation amplifier with differential input with single supply.  I will use it to measure AC line voltage.  G = 1 is preferred.  I used ACPL-C78A before but it fails-not-safe to +5V!


  • Hello Sam,

    To the best of my knowledge the only device with a differential fail-safe output of 0V on a 0V common mode is the ISO224.

    A couple of devices you may want to view are the AMC1300, AMC1302, and ISO224.

    The ISO224 has a differential output of +/-4V centered on a common mode of VDD2/2. The Fail-safe output is 0V differential on a 0V common mode. An additional comparator circuit is required to monitor the fail-safe output to distinguish between a floating input and the fail-safe output. I wrote an app note about the fail-safe output feature of the ISO224 and you may need to implement a stage similar to what I show:

    List of isolated amplifiers for reference: