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Current monitoring using AMC1100

Other Parts Discussed in Thread: TIDA-00555, AMC1100, AMC1100EVM, ADS7263

Hi,

My name is Idan and I'm electronic engineering at the Israeli Aerospace Industry.

In my application I have I have to use isolated shunt resistor in order to measure the input current for a full bridge inverter (with inductance load). The current range is 0.1A-4A and the phase voltage is 300V. I think I that can use the AMC1100 Fully-Differential Isolation Amplifier for the current measurement. In your web side I found the "Isolated Current and Voltage Measurement Using Fully Differential Isolation Amplifier", TIDA-00555 Card/system (attached herewith) that might be perfect to me. In order for me to use the AMC1100 in my project (in quantity of a hundreds), I really need for you to answer the following questions:

  1. In Figure 1 of the TIDA-00555 block diagram it seems like the current shunt is located on the high-side on the ~300VDC (230VAC). The problem is that according to the datasheets, the amplifier VCM is only –0.16 to VDD1 (Basically allow only low- side shunt measurement). Am I right? You can see this repeated principle in Figure 36. The AMC1100 in an E-Meter Application in the AMC1100 datasheet (High side measurement using AMC1100, assuming that L1-L3 in larger then VDD1A-VDD1C respectively?   
  2. If I'm right about the first question, is it possible to use the AMC1100 in the low side instead?
  3. In the TIDA-00555, you mentioned that the TIDA-00555 design can also be used to measure DC or a 400-Hz signal. Why is that? According to the AMC1100 datasheet, the input bandwidth is 60 kHz min. Can I use this amp to measure signals at ~30kHz for example?
  4. Can I test the current monitoring principle on the AMC1100EVM?  
  5. If this amplifier is not suited to my application can you suggest a different device (to ether/ both high side or low side measurement, Isolated)

Thanks a lot,

Idantidua58.pdf

 

 

  • Hi Idan!

    I was not one of the authors of the TIDA-00555 document, but I'll bring this post to their attention and let them give you specifics on that reference design.

    You can use AMC1100 in either a high-side or low-side current measurement application. You are right that the input VCM is limited to the VDD1 rail, so you'll need to create a floating supply when doing high-side measurements. The AMC1100EVM can certainly be used to test out various current monitoring situations. It's been designed to allow isolated measurements, but it has not been certified to any high voltage standards.
  • Hi Tom,
    First, thank you for your quick response…
    You mentioned that the AMC1100 amplifier is not certified to work in high voltage, so in Figure 36 in the datasheets, the L1-L3 voltages in only limit to VDD1A- VDD1C (which is about 6V max)?
    Do you have any recommendation for isolated amplifier that certified to high voltage standards (~350VDC)?
    Thanks alot,
    Idan
  • Hi Idan,

    You misunderstood what I wrote. The AMC1100 is rated to withstand 4250 Vpeak with a continuous working voltage of 1200 V, so there is no issue in using it for your application of 350 VDC. The EVM for the AMC1100 is designed to withstand those voltage levels, but it was not certified to any high voltage standards. Figure 34 shows how the current monitoring circuits of Figure 36 would be powered. The VDD1 source is a floating supply providing 5V relative to GND1 so that you do not exceed the input common mode range of the device. The three voltage monitoring circuits of Figure 36 are referenced to neutral.
  • Hi Tom,

    Thank you very for clearifiy the point that VDD1 source is in fact floating- I have to be sure that I using the amplifier according to the design guidline before starding the prototype production.

    Attached herewith is the final application according to my knolage (Figure I).

    1. Am I using the amplifier in it's bast and rubust way?

    2. Is it going to be a problem at the first power up (TP2 is in 350V while TP1 is Grounded due to the capacitor voltage transient)?

    3. Whould it be simplier to use a low side (Figure II) measurement? (No need to floating power supply)  

    4. Do you recommnd that I'll use a amplifier that already contain a high common-mode voltage? (such as the AD8479 (±600V) and to add galvanic isolation in the folloing next stage)

    Again, thank you very much!

    IdanFigure I- High Side.pdfFigure II- Low Side.pdf

  • Hi Idan,

    Either one of your approaches would work with the AMC1100. What is the digitizer that you plan to use? Are you using an stand alone ADC or one built into a microcontroller/DSP? You'd have to consider bi-polar supplies with the ADxxxx part and then possible scaling/level-shifting to get the analog output into the correct range for your digitizer.
  • Hi Tom,

    Now that we are frinds… J- thank's agine for your reply...

    The shunt resistor and the AMC1100 amplifier are desine to implement on an electric card right next to hight inductive load (Very Very harsh environment). The next component is a stand alon ADC that will be placed in different electronic card- an FPGA card (the whole hardware is now been define). The problem is that the FPGA card is located several fit from shunt card and it will be desige a stand alon isolated card. So, I need that the right hand side of the AMC1100, which is the shunt card, to be connected directly to isolated ADC (in the FPGA card) prefered with SPI interface, with voltage level of 3.3V to the FPGA and 5V to AMC1100). Can you recommend on such device?

    In a low side measurement, I don’t realy need the negative power supply, right? ("-5.0V_USH", see figure I/II that I send in the previose correspondence). It's only for protection the V- pin, right?

    Thanks in advance…

    Idan 

  • Hi Tom,
    Now that we are frinds… :)- thank's agine for your reply...
    The shunt resistor and the AMC1100 amplifier are desine to implement on an electric card right next to hight inductive load (Very Very harsh environment). The next component is a stand alon ADC that will be placed in different electronic card- an FPGA card (the whole hardware is now been define). The problem is that the FPGA card is located several fit from shunt card and it will be desige a stand alon isolated card. So, I need that the right hand side of the AMC1100, which is the shunt card, to be connected directly to isolated ADC (in the FPGA card) prefered with SPI interface, with voltage level of 3.3V to the FPGA and 5V to AMC1100). Can you recommend on such device?
    In a low side measurement, I don’t realy need the negative power supply, right? ("-5.0V_USH", see figure I/II that I send in the previose correspondence). It's only for protection the V- pin, right?
    Thanks in advance…
    Idan
  • Hi Idan,

    The output of the AMC1100 is differential, so you want to use a differential input ADC, something like the ADS7263 as shown on the AMC1100 datasheet. Running an SPI interface over 'several feet' could be problematic, that's a bidirectional interface and you need to be able to send data to and receive data from the ADC on the same clock edge. Long cable lengths can cause significant delays, corrupting data. It would be better to have the ADC closer to the FPGA and let the differential output of the AMC1100 travel the longer distance.