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AMC1304M05: AMC1304 bit stream output - possible connections to MCU

Adi Selimovic
Intellectual 560 points
Part Number: AMC1304M05
Other Parts Discussed in Thread: AMC1200, AMC1301, AMC1210, MSP-EXP430FR5994, MSP430FR5994

Taking into account available reference designs, isolation amplifier AMC1304 has built-in sigma-delta modulator (16-bit resolution, ENOB 13.2 bit) and it is connected with MSP models that have also built-in sigma-delta digital filters in order to suppress quantization noise and improve resolution. The question is the following: What are the possibilities to use AMC1304 with MSP models which do not have integrated sigma delta digital filters and if it is possible, what is the best way to do it? 
Thank you in advance,
Adi

  • 0
    TI__Guru**** 168485 points
    Hi Adi,

    There really is no good way for any MSP430 without the sigma-delta filter module to accommodate the bit stream from the AMC1304M05. The better option would be to consider using one of the isolation amplifiers, perhaps the AMC1301 or AMC1200.
  • 0 in reply to Tom Hendrick
    Intellectual 560 points
    Hi Tom,

    What is ENOB of both models?

    Best regards,
    Adi
  • 0 in reply to Adi Selimovic
    TI__Guru**** 168485 points
    Hi Adi,

    The AMC1301 and AMC1200 are analog in/analog out (they are isolation amplifiers) so ENOB is not specified. Assuming you might feed those outputs to another ADC, you would need to consider ENOB at that point. In general though, the amplifiers are ~12-13 bit accurate.
  • 0 in reply to Tom Hendrick
    Intellectual 560 points
    Hi Tom,

    In that case it would be critical to use one of these isolation amplifiers for current measuring due to its accuracy requirement (>12 bits). What is your advice to overcome this problem?

    Best regards,
    Adi
  • 0 in reply to Adi Selimovic
    TI__Guru**** 168485 points
    Hi Adi,

    You could use the amplifier with the SD-24 of an MSP430. You can use one of the MSP430's with the Delta-Sigma Filter Module and get into the ~14 bit range using the AMC1304M05. You could also use the AMC1210 with the AMC1304M05 and an MSP430 without the filter module if you have the board space available. There are also C2000 series processors with the Sigma-Delta Filter Modules, so that is another option for you.
  • 0 in reply to Tom Hendrick
    Intellectual 560 points

    Hi Tom,

    As I want to use one of existing MSP LaunchPads, SD-24 is not an option due to lack of built-in digital filters. (In general, I am trying to implement isolated 3-phase energy measurement)

    In a case of combining AMC1210 and AMC1304M05, which unit is connected to external clock in order to provide synchronous sampling? AMC1210 can be connected to the LaunchPad via SPI as ADC?

    The reason I have not considered C2000 series because all reference designs about metering are done by MSP series.
    Would oversampling help in any case?

    Best regards,
    Adi

  • 0 in reply to Adi Selimovic
    TI__Guru**** 168485 points

    Hi Adi,

    With the AMC1200 or AMC1301, you would connect into whatever ADC you have available on the MSP430, if that ends up being the ADC-12, you are looking at ~10-11 bit's ENOB at best. The AMC1210 is a S-D filter chip that would talk either 8-bit parallel (PORT reads/writes to the MSP430 are possible, but there is no true 'parallel interface' on the MSP430 so it's all bit-banged essentially) or through SPI. You can feed a timer from the MSP430 to the AMC1210 to act as a modulator clock for the AMC1304M05, or you can use an external oscillator.

  • 0 in reply to Tom Hendrick
    Intellectual 560 points
    Hi Tom,

    The previous plan was to use AMC1200 or AMC1301 with external ADC (e.g. 16 bit SAR) and than MSP Launchpad. I hoped to achieve 13 bits of resolution.

    In a case of solution with AMC1210, its clock is fed directly from MSP or via clock buffer?

    Thank you for patience and helping me,
    Adi
  • 0 in reply to Adi Selimovic
    TI__Guru**** 168485 points

    Hi Adi,

    Using an external 16-bit SAR is also a possibility. Just keep in mind that the AMC1200 and AMC1301 both have differential outputs. The AMC1200 output common mode voltage varies based on the VDD2 voltage (2.45 Vcm out with 5V supply, 1.44 with 3.3V) while the AMC1301 output is fixed at 1.44 Vcm. Ideally you'll choose an ADC with a differential input, otherwise, you can convert the output to single ended and perhaps scale a little to suit the FS input range of the ADC (see this tech note for details: www.ti.com/.../sbaa229.pdf ).

  • 0 in reply to Tom Hendrick
    Intellectual 560 points
    Hi Tom,

    Taking into account all previously mentioned, an option with external ADC seems reasonable if it provides 13-bit resolution. There are several ADCs on the market which match with differential output of AMC1200 and AMC1301.
    In this case ADC's clock is fed directly from MSP or via clock buffer? When the clock buffer must be used in general?

    Best regards,
    Adi
  • 0 in reply to Adi Selimovic
    TI__Guru**** 168485 points
    Directly from the SPI port, assuming everything is on one board. If there are cables involved, you may need a buffer.
  • 0 in reply to Tom Hendrick
    Intellectual 560 points
    Hi Tom,

    So it doesn't matter which voltage is set to low voltage side (3,3 or 5 V) of AMC1301 if I want to connect it to existing LaunchPad (with internal ADC) or another approach with external ADC?

    Best regards,
    Adi
  • 0 in reply to Adi Selimovic
    TI__Guru**** 168485 points

    Hi Adi,

    No, for the AMC1301 it does not matter how you connect the low side power.

  • 0 in reply to Tom Hendrick
    Intellectual 560 points
    Hi Tom,

    I am in the last stage of making the AFE layout which will be directly connected to LaunchPad or external ADC. Therefore, I will probably use cables. Are there any potential problems with signal quality in this case? What are your tips?

    Best regards,
    Adi
  • 0 in reply to Adi Selimovic
    TI__Guru**** 168485 points

    Cables on the inputs or outputs?  Either way, I would most likely use a shielded twisted pair.

  • 0 in reply to Tom Hendrick
    Intellectual 560 points

    Hi Tom,

    AFE analog output is planned to be connected with the analog input of a Launchpad. Usually, models which have everything on one board, low pass filters (for instance) are very close to MCU. In my case, these filters are close to output pins of AFE board.

    Best regards,
    Adi

  • 0 in reply to Tom Hendrick
    Intellectual 560 points
    Hi Tom,

    According to your response:
    "Using an external 16-bit SAR is also a possibility. Just keep in mind that the AMC1200 and AMC1301 both have differential outputs. The AMC1200 output common mode voltage varies based on the VDD2 voltage (2.45 Vcm out with 5V supply, 1.44 with 3.3V) while the AMC1301 output is fixed at 1.44 Vcm. Ideally you'll choose an ADC with a differential input, otherwise, you can convert the output to single ended and perhaps scale a little to suit the FS input range of the ADC (see this tech note for details: www.ti.com/.../sbaa229.pdf )."

    Does it mean that for AMC1200, the low voltage side MUST be 3.3 V in order to be connected with a LaunchPad (MSP-EXP430FR5994)? Otherwise, the input voltage range of an ADC will be exceeded?

    Best regards,
    Adi
  • 0 in reply to Adi Selimovic
    TI__Guru**** 168485 points
    Hi Adi,

    The input to the ADC12 on the launch pad cannot exceed AVdd, which is 3.3V. It would appear as though the MSP430FR5994 has the option to do differential ADC measurements, so there should not be any issues connecting the AMC1200 to it when you power VDD2 from 3.3V.
  • 0 in reply to Tom Hendrick
    Intellectual 560 points
    Hi Tom,

    I will apply differential ADC measurement and the maximum input voltage on AMC1200 in the measuring circuit is 150 mV. In terms of PCB design, it is an additional cost to provide 3.3 V path in comparison with the AMC1301 case which needs only 5 V for both, high and low voltage side.

    Best regards,
    Adi
  • 0 in reply to Adi Selimovic
    TI__Guru**** 168485 points
    Hi Adi,

    The AMC1200 (and the AMC1304 we started with) are supposed to provide isolation from input to output, so generally they require two power supplies. You can power the high side from 5V and I suspect there are a couple pins on the launchpad that you could use to bring 3.3V and GND from that board to the one you are putting together to power the secondary side of the AMC1200.