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AMC1100: Supply Voltage

Part Number: AMC1100
Other Parts Discussed in Thread: AMC1300, AMC1200


I am using AMC1100 with a zener diode structure, datasheet fig. 39, to provide 5V for the High Side. The aim was to supply 5V to AMC1100 directy from input voltage, without using an extra isolated voltage regulator. However, the problem is that without High Side voltage supply (Below approx. 3V) the output set to 2.5V or -2.5V (VOUTP or VOUTN). 2 problems with that configuration:

1) When the input signal is off, the output is 2.5V.

2) It is 2.5V or -2.5V.

Is it expected or am I not using the device correctly?

If it is expected, a design without an extra regulator makes no sense since 0V (The input is off State) is not detected. (Maybe it can be detected with a condition for 2.5V level since output voltage will not exceed 2V during the normal operating.)

  • Hi Onat!

    Welcome to our e2e forum! The output of AMC1100 will saturate to either full-scale positive or full-scale negative with no voltage applied to VDD1.  We did not incorporate a 'missing VDD1' fail-safe feature in this device (see AMC1300, section 8.3.3 as an example of a device with such a feature).  The outputs follow the last bit decision that went over the isolation barrier when VDD1 is missing (your 3V level sounds about right). If you had VDD1 applied and 0V input to the AMC1200, you should expect to see 0V (differential) on the outputs.

    You could certainly detect this as an abnormal condition if you are only concerned with +DC input levels.

  • Hi Tom, 

    Thank you for the answer. I have one more question about your last statement. With a differential ADC I also expect to detect "this condition (VDD1 is below 3V when Differential Output of AMC1100 is |2.5V|)" with AC input. Could you please explain further?

  • Hi Onat,

    Since you mentioned that you are using the actual voltage to be measured as a source to power the AMC1100, I assumed this is just a DC voltage measurement.  If you are rectifying an AC voltage before applying it to the zener, you could measure an AC input.