LMK04228: use SYSREF clock in anthor clock group

Jerry Chen

Part Number: LMK04228
Other Parts Discussed in Thread: LMK04828,

Hi there,

I would like to confirm one thing quickly. My customer is using LMK04228 (LMK04828) for a JESD204B use case. The 245.76MHz device clocks are on clockout0 and clockout2. But the 0.96MHz sysref clocks are on other clock groups(CLKout11 and CLK0ut13). I don't think there is anything different in performance and function compared to making Device clock and SYSREF clock in the same clock group. Is it correct?

I also attach the output setting in TICS Pro. 122.88MHz on CLKOUT9 has been changed to CLKOUT10.

Thanks.

over 5 years ago

0 Derek Payne over 5 years ago

TI__Mastermind 34270 points

Hi Jerry,

The SYSREF divider circuitry is powered on a separate VCC pin from the clock group power supplies, so the divider noise should not crosstalk into the clock outputs. However, if the SYSREF is running continuously while physically close to the high frequency output (for example, if CLKout0 is 245.76MHz and CLKout1 is 0.96MHz), the 245.76MHz clock will likely see a large 0.96MHz spur. We usually recommend that customers use the SYSREF circuit in pulsed mode to prevent this physical distance crosstalk spur. If the SYSREF is being used in pulsed mode, there should be no harm in placing SYSREF outputs immediately next to device clock outputs.

Regards,

Clock & timing

Clock & timing forum

LMK04228: use SYSREF clock in anthor clock group