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ADS8319: Data converters forum

Y.Ottey
Mastermind 6145 points

Part Number: ADS8319
Other Parts Discussed in Thread: ADS8864

Dear all,

I would like to ask about Daisy-Chain option in ADS8319.

For the ADS8319, how many channels can be sampled simultaneously using the Daisy-Chain Option?

I need to know the answers above quickly

I would appreciate it if you could get back to me right away.

Best Regards,

Y.Ottey

  • 0
    TI__Guru 52430 points

    Hello Y.Ottey,

    It depends on a number of factors, including the sample rate.  What sample rate do you need?  What digital supply, +VBD, do you want to use?

    More specifically, the maximum number depends on the time needed to shift all of the data from each of the daisy chained ADC's.  Figure 58 in the datasheet has the timing details along with Tables 7.6 and 7.7.

    Example (+VBD=5V, SCLK=50MHz):

    500ksps: 1 device (will not support daisy chain at full speed)

    400ksps: 3 devices

    300ksps: 5 devices

    200ksps: 11 devices

    100ksps: 26 devices

    If you want your digital IO to operate at 3.3V, then the following numbers will apply:

    Example (+VBD=3.3V, SCLK=33MHz)

    500ksps: 1 device (will not support daisy chain at full speed)

    400ksps: 2 devices

    300ksps: 3 devices

    200ksps: 7 devices

    100ksps: 17 devices

    Regards,
    Keith Nicholas
    Precision ADC Applications

  • 0 in reply to Keith Nicholas
    Mastermind 6145 points

    Hi.Keith,

    Thank you for reply.

    Our customers will use it under the following conditions.

    VBD：5.5V

    Sample rate:250kSPS(Max)

    They also want to sample 53 channels simultaneously.

    If SCLK = 50MHz and sampling rate is less than 100kSPS, is this simultaneous sampling possible?

    Is there any device that can be used this way?

    I would appreciate it if you could get back to me right away.

    Regards,

    Y.Ottey

  • 0 in reply to Y.Ottey
    TI__Guru 52430 points

    Hello Y.Ottey,

    You do not need to use daisy-chain mode to get simultaneous sampling.  You can connect the CONVST of 53 devices together (the host MCU Output pin must drive this load) and all 53 devices will then simultaneously sample their respective inputs.  The challenge is to then get all of the data transferred into the host MCU/FPGA before the next conversion starts.

    At 100ksps, you should be able to transfer all of the data from 26 devices using an SCLK=50MHz.  You could tie all 53 ADS8319 CONVST pins together to get simultaneous sampling and use 3 SPI ports to communicate with 3 daisy-chain's of devices.

    ADS8864 is a newer device that supports faster data transfer.  Using SCLK=66.6MHz and 100ksps, you can daisy chain 35 devices together.  You can connect 53 CONVST pins together and use two SPI ports (1 daisy chain of 27 devices and the other chain of 26 devices) to transfer all of the data. 

    If the sample rate is further reduced to 70ksps, the ADS8864 with SCLK=66.6MHz would support a single daisy-chain of 53 devices.  (ADS8319 would support a maximum sample rate of 50ksps when daisy chaining 53 devices with SCLK=50MHz)

    Please note the ADS8864 can be used with a 5V reference, but the analog and digital supplies are specified at 3V.

    Regards,
    Keith