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ADC12J4000/2700

Jani Isoo
Intellectual 1930 points
Other Parts Discussed in Thread: ADC12J4000, ADC12J2700, LMK04828, TRF3765, LMX2582, ADC12J4000EVM

Hi,

On the TSW14J56EVM development board the LMK04828BISQ seems to be used for clock redistribution, not for its advertised jitter cleaning function.  The 2.7GHz clock is provided by the TRF3765IRHB.  Is the LMK04828BISQ included because of its ability to handle the 4GHz clock when the ADC12J4000 is fitted?

 

If we wanted our design to cater for either the ADC12J2700 or ADC12J4000 what are the minimum set of clock generation ICs would we need to use?

 

How essential is the temperature monitoring of the ADC12J2700 or ADC12J4000?  Our product will need to operate over the temperature range 10 degrees Celsius to 40 degrees Celsius, ideally with natural convection, but a fan can be included if required.

 

 Thanks,

Jani

  • 0
    TI__Mastermind 44680 points

    Hi Jani

    The LMK04828 is included to provide flexible support for the JESD204B SYSREF and FPGA Device Clock requirements of the system. The FPGA requires 1 or 2 clocks in addition to the JESD204B SYSREF. The ADC requires a device clock and also needs SYSREF if JESD204B Subclass 1 deterministic latency is required.

    The TRF3765 is used to give clock frequency flexibility from 1000 to 4000 MHz. The LMK04828 does have PLL/VCO circuitry, but does not have full coverage of that frequency range. For that reason we use the combination of the TRF3765 as a clock synthesizer, plus the LMK04828 to create the clocks for the FPGA and the SYSREF for both the FPGA and the ADC.

    If you need to operate with clocks at either 4000 or 2700 MHz I would recommend a similar architecture using either the TRF3765 or LMX2582 as the clock synthesizer and the LMK04828 to provide the FPGA and SYSREF clocks.

    On the ADC12J4000EVM at 4 GSPS in DDC Bypass Mode, and Background Calibration mode I see around 50-55 degrees C of rise above ambient (76 junction with 23.8 ambient), so with an ambient range from 10 to 40 degrees Celsius a fan is likely not required. I would recommend including test points so an external temperature sensor board (LM95233EB) can be used during development to check the ADC junction temperature.

    Best regards,

    Jim B