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LMK04832: the questions of SYSREF generation

Kailyn Chen
Genius 9560 points
Part Number: LMK04832
Other Parts Discussed in Thread: LMX2594,

Hello,

Both LMK04832 and LMX2594 have the function of  the control signal to generate SYSREF.

When LMK04832 worked at clock distribution mode,  the rising edge of SYNC  is used as the trigger.

While LMX2594 worked host mode, the rising edge of SysRefReq is used as the trigger.

If  the trigger control is periodic signal, and the period is just equal to the( SYSREF period *pulse numbers), pulse number is configured by SYSREF_PULSE_CNT register.  So the question is about the output of SYSREF, if the output of SYSREF is continuous pulses or the pulse trains with same interval time? 

Could you please help to analyze?

Best regards

Kailyn

  • 0
    TI__Genius 11900 points

    Hello Kaitlyn,

    On the LMX2594 the SysRef can be used in a repeater mode (SYSREF_REPEAT = 1), which just echos the SysRefReq pin, after being reclocked to the fINTERPOLATOR frequency and then fOUT (from RFoutA). In this case assuming the input is a continuous clock the output is a continuous clock. If the input is a single pulse, the output would also be a single pulse.

    I believe you are talking about the other case where SysRefReq is held high, after an initial rising edge. Here the frequency of the SYSREF output is configured by the device and is a divided down frequency from the VCO frequency. SYSREF_DIV_PRE and SYSREF_DIV determine what this divider is. The output can either be a continuous clock or a series of pulses. The number of pulses can be defined by the SYSREF_PULSE_CNT register. The frequency and time period of each pulse will be the same regardless of whether you use SYSREF_PULSE = 1 or not.

    On the LMK04832 you essentially have the same options, you can repeat what is at the input of SYNC/SYSREFREQ pin, you can generate a SYSREF from the VCO frequency (continuous or specified set of pulses) and you can reclock the VCO generated SYSREF to a SYNC input.

    Thanks,

    Vibhu