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ADS8557: Simultaneous sampling with External clock, best practices for jitter cleaning

Alberto Carboni
Prodigy 95 points
Part Number: ADS8557
Other Parts Discussed in Thread: ADS8548, ADS8558, ADS8528

Hi all

I have a reference clock created with a 4046-PLL-based frequency multiplier, given the nature of the source it features low jitter, that should make no problem.

In particular I already tested it with a National Instruments board (NI - USB 6356) that feature an external clock input channel, my question is if I want to use it in an embedded solution with the aforementioned ADS8557 should I consider also the presence of a LMK0480x to clean that jitter or the ADS8557 would work without issues or the internal circuitry needs a Jitter cleaning section?

In particular, do you know if there are available evaluation boards with an external clock reference?

The data converters I am considering are:

ADS8557
ADS8548
ADS8558
ADS8528

The next step will be to interface it with a real-time uC board (probably a Delfino-based board), so if you already know a TI solution that already embeds this let me know.

Thank you

Alberto

  • 0
    TI__Mastermind 35520 points

    Hello Alberto,

    Thanks for your query about our SAR ADC on E2E. For ADS8557, external conversion clock(XCLK) can be selected by setting CLKSEL bit high (bit C11 in the CR register) in software mode and the clock can be applied on Pin 27, this clock definitely will affect conversion accuracy because it will be used as conversion clock. I didn't use a clock from 4046 PLL as ADC's conversion clock, so not sure how clean clock from this device, but we have a evaluation board ADS855xEVM with a external clock connector J6, so you can use this EVM board to check whether you need a additional device to clean this clock. The web link for this EVM:

    www.ti.com/.../ads8557evm

    Actually, this ADS8557 ADC has an internally-generated conversion clock which mandatory in hardware mode and also optional in software mode. In default mode, the device generates and uses an internal clock. ADS8558 and ADS8548/28 have same options for XCLK.

    Thanks and regards

    Dale

  • 0 in reply to Dale Li
    Prodigy 95 points
    Hi Dale,

    Thank you for your quick answer, I'll update you

    Regards

    Alberto