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AMC1100 Vout with VDD1 removal

Ed Walker
Prodigy 5 points
Other Parts Discussed in Thread: AMC1100, AMC1305L25, TIPD121

I am using the AMC1100 circuit from the datasheet Figure 31 (although it’s single-ended voltage mode, but otherwise the same) to monitor a 28V input.


When VDD1 goes to zero, we are wanting to see Vout go to zero to indicate an input power failure.

However, when the input side power VDD1 goes away, the output differential signal goes to full scale most of the time instead of zero as expected, but occasionally have seen it go to zero a few times.   

Our system has batteries to power it when the main input power is not present. 
Therefore it can have power on the VDD2 side, but not on the VDD1 side. 

Please comment on the operation when VDD1 is removed with VDD2 present.
Any suggestions to accomplish the desired goal?

 

  • 0
    TI__Genius 9975 points

    Hello Ed,

    Unfortunately there is no provision in the AMC1100 to alert the user on whether the saturated output of the device is due to a large input or due to loss of power on the high-side.

    Some options you have are:

    1)      Use a delta-sigma modulator instead of an amplifier (provided that you have a digital filter on the controller side). The AMC1305 products do have the ability to discern between a saturated input and loss of power on the high side. (See for example the AMC1305L25 datasheet).

    2)      Use an AMC1100 plus a comparator to monitor the VDD1 power supply of the system. Alternatively, a simpler component such a single channel isolator or photocoupler could be used.

    3)      Use a combination of the power supply you currently have with a power supply derived from VDD2 as shown in the TIPD121: “Design Reference Guide, 0-5 A, Single-Supply, 2 kV Isolated Current Sensing Solution (SLAU521). You can use a couple of low forward bias diodes in order to automatically select which supply feeds VDD1. If either supply collapses the other one takes over (provided that not both of them are removed of course.)

    Hope this helps.

    Best regards,

    Jose