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ADS1278-EP: Two devices that work in parallel.

Part Number: ADS1278-EP

Hi Team,

We have received this inquiry from our customer.

Regarding the ADS1278-EP device: two devices that work in parallel.
Our system works with two ADS1278-EP in "high speed" protocol and SPI protocol in parallel.
CLK       = 13.5MHz;
CLKDIV =1;
SCLK      = 12MHZ;
The goal is to sample simultaneously by the two ADS's when the accuracy of the sampling time difference between the two devices should be better than 8 microsecond. Is there an application that meets this requirement?

Regards,

Danilo

  • Hey Danilo,

    The channels in a given device will be synchronized to less than 500ps of each other. While we don't spec the deviation between devices and this will depend on other variables like matching clock lengths, I think two devices running from the same clocks with good layout are very likely to be within 8us of one another.

    That said in order to guarantee this you could use the SYNC pins of the devices to send a pulse to each device to synchronize them to within 1 clock cycle. This is demonstrated in figures 73 and 74 in the datasheet.

    Best,

    Zak

  • Hi Zak,

    Thank you for your response. We have received this feedback from our customer.

    Reference to Datasheet Figure 70. Synchronization Scheduling (SPI Protocol)
    It is definitely mentioned that tNDR time is between 127 and 128 conversions (1 / fDATA)
    Which means that in our application it has an interval of 1 / (1024 * 50) 20ms, unfortunately greater than 8 microseconds

    Regards,

    Danilo

  • Hi Danilo,

    I just want to clarify that the data ready timing you are describing is not the same as the phase matching between channels. There will be a delay once a sync pulse is issued before the data is available as the modulator has to re-settle, but assuming all devices receive the same pulse their outputs will be much more aligned from that point forward and can be periodically re-aligned with additional sync pulses as needed if the clocks begin to drift too much.

    Best,

    Zak