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SD16_A SD16 Specifications

Shashank Chintalagiri
Prodigy 195 points
Other Parts Discussed in Thread: MSP430F47126

I've been evaluating the SD16/SD16_A devices for using as an ADC and have a few questions:

* I've noticed that different documents have different information about whether the ADCs are separate or the inputs are multiplexed. I'm evaluating the MSP430F47126 for the moment. Does this have 6 separate sigma-delta cores or are the inputs multiplexed? Alternatively, is it possible to get ADC data from all 6 channels simultaneously at 32KHz, assuming I'm fine with 9-bit data.

* Can the individual ADCs, if they exist, be triggered simultaneously on this device? There were forum posts suggesting the bits were reserved.

* A signal range of 0.6V is fairly low for what I have in mind. At the moment I'm considering using Analog Devices' AD8475 on the signal to get +/- 1.2V range, though I'd like to be able to get a wider input range on the input. My signal sources are expected to be far away from the ADC and so far we've been using a +/- 5V differential pair to send the signals to the data acquisition system. Is there an appnote available or some pointers anyone could give me on how his sort of ADC input range can be effectively put to use?

* This question is probably overly subjective, but from the specs I've seen, I'm wondering if SD16 is better than ADC12 with oversampling. What are the use cases where SD16 becomes the better option?

  • 0
    Prodigy 195 points

    An additional related question :

    * The datasheet specifies analog input range to be +/-Vref. Is this input range with respect to ground or in terms of (IN+ - IN -), i.e, if I were to use an MSP430 such as the MSP430F47126 powered by 0,3.3V, could I connect to it an analog signal of (IN+ = 0.6V, IN- = -0.6V) and vice versa and expect to be able to make good ADC measurements?

  • 0 in reply to Shashank Chintalagiri
    Guru 227245 points

    On MSPs where the SD16 inputs are on dedicated pins (not shared with digital I/O), the input range is indeed +-0.6V. Most MSPs with multiple individual 1-channel SD converters, this is the case.
    On the MSPs with shared analog/I/O pins (usually those where there is only one SD with multiplexed inputs), the clamp diodes limit the negative voltage, so the input voltage must be positive (or is cut to Vss-0.2V)

    The main reason is that the first type of MSPs is built for energy metering purposes, where voltage and current need to be measured simultaneously (hence the individual SD modules) and the input is an AC signal form a shunt or current transformer (so a symmetrical positive and negative input range is required).

     However, for long distances, you should consider using a current loop. A simple OpAmp can do the conversion on the sensor side
    http://www.tradeofic.com/Circuit/15718-Power_op_amp_voltage_current_converter.html

    On the MSP side, you’ll have a shunt that converts the current back into a voltage.

  • 0 in reply to Jens-Michael Gross
    Prodigy 195 points

    Thanks for the reply!


    That sounds reasonable. I think I'll stick to differential voltage signals for the moment, though. The need for precision resistors for a lot of voltage-current-voltage conversions is something that is difficult to satisfy.

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