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Help with ADC selection for data acquisition system

Stephen Moore
Prodigy 250 points
Other Parts Discussed in Thread: ADS8319, ADS1225, ADS8327, ADS1174

Greetings, I am trying to select an ADC for a prototype data acquisition system. The prototype is to be tested late this year or early 2013. Field trials are expected in 2014. The prototype part selection has low cost sensitivity (20 systems expected), and may represent higher performance than will actually be required for production. We can always "trim" the prototype performance down with software to emulate a cheaper production part. Production has more cost sensitivity.

The DAQ has three analog input channels read by a microcontroller. The three channels need identical technique and simultaneous sampling. Specifications below:

Sample Rate:  10ms / 100sps

Resolution: 16 bits or better

Analog Input (channel 1): 0.5 to 4.5 volts, 2.5V centerpoint, excursions to 0 to 5V expected

Analog Input (channel 2): 0.5 to 4.5 volts, 2.5V centerpoint, excursions to 0 to 5V expected

Analog Input (channel 3): 0 to 5V full scale

Digital I/O: 3.3V logic SPI bus, microcontroller has one free SPI channel and a few additional pins for I/O

I could select a single multi-channel chip or three single-channel chips on a SPI bus. Some first impressions were the ADS1225 (single channel delta-sigma) or ADS8319 (single channel SAR). The delta-sigma is interesting because my sample rate requirement is low (100Hz), which allows the delta-sigma to offer an oversampling filter advantage.

Any suggestions?

  • 0
    TI__Mastermind 46290 points

    Hi Stephen,

    With the information you've given us so far those converters don't look like bad choices. You might also consider the ADS1174 to bring everything into one IC. In single channel devices all you're really looking for is a differential converter with a convert start signal that is not the chip select or frame sync signal. The ADS8327 might fit here as well. If you have any further information about your application we can try to give a more refined set of suggestions.

  • 0 in reply to Kevin Duke
    Prodigy 250 points

    Greetings,

    The ADS8327 pseudo-differential, allowing a 4.2V reference and the Ain(-) pin should be tied to common. This essentially makes the chip a single-ended part with maximum 4.2V at Ain(+). Unless I cut my signal (not desired), this is below spec. I do like the pseudo-differential configuration, if the Ain(+) could handle up to 5V, it would be an ideal setup.

    Now the ADS1174. The sheer amount of interface pins is daunting - I don't have that many to spare - but a quick glance at the datasheet suggests most of these can be hard-configured and not need microcontroller interface (or at least reduced interface). The only gripe is the data rate can't be adjusted by changing the oversampling rate, but this is a minor complaint. As the native data rate is ~50ksps, I'll either be ignoring a lot of the output, or manually triggering each conversion.

    Thanks for the advice. This can be a difficult job given the sheer number of datasheets to examine in the process.