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ADS1282-HT: Is it possible to run the ADS1282 in continuous sync mode using sync command (sync tied HI)?

Zachary Faber Manning
Prodigy 10 points
Part Number: ADS1282-HT
Other Parts Discussed in Thread: ADS1282

Based on the datasheet, it's unclear to me whether the ADS1282 can use the sync command rather than the sync pin when it is in continuous sync mode. The sync pin would be tied high in this application, and a sync command would be issued for every sample with a 4ksps sample rate. By every sample, i mean the decimated post-FIR rate that is read back over SPI, not the underlying 128kHz rate.

Also, if multiple ADS1282s are running off the same external clock, will they run in lockstep after an initial sync, or will they slowly drift out of sync and need to be periodically resync'd?

Thanks!

  • 0
    TI__Mastermind 44690 points

    Hi Zachary,

    Welcome to the TI E2E Forums!

    Continuous Sync Mode

    The Continuous Sync mode of the ADS1282 is intended to be used with a clock signal connected to the SYNC pin of the device. This clock signal needs to have a period that is an integer multiple of the post-processed output data rate (often a 1 Hz GPS pulse is used here). This clock signal is then provided to multiple ADCs and ensures that all devices remain in sync when running off of multiple independent (asynchronous) master clocks, as is sometimes required by a distributed network of data acquisition nodes. If the master clock of any node drifts out of sync with the SYNC clock, then the ADC conversion is restarted (and the digital filter reset) to restore synchronous operation. (i.e. The sync pulse only restarts conversions when the device gets out of sync by more than 1 fCLK period)

    I'm not entirely sure if Continuous Sync mode could be used with the SYNC SPI command, but even if it could it would likely be very impractical. Most SPI peripherals on an MCU would not be able to issue the SPI command to within the 1 fCLK period required to keep devices continuously converting. Each SYNC command would likely force conversions to restart and you'd observe a low data throughput due to the digital filter settling time.

    Pulse Sync Mode

    If instead you have the ability to provide a single external clock source to all ADCs in your system then you wouldn't need to use Continuous Sync mode. You could clock all ADCs from the same clock and then issue a SYNC command or SYNC GPIO pulse to all devices at once. This will ensure that all devices start converting on the same clock edge edge. In Pulse Sync mode, the ADS1282 conversions always restart when a SYNC pulse (or SYNC SPI command) is given, so you'd only need to synchronize the devices once after initialization or after modifying register settings (since this operation also restarts the conversion process).

    With all devices sharing a single clock signal, all devices (or conversions) will drift with the clock signal but will remain synchronized.

    I hope that helps!