LMX2594: SYNC Signal requirements

Hans

Part Number: LMX2594
Other Parts Discussed in Thread: LMK04832

Hello Team,

page 11 of DS:

What is the reference point of the OSCin rising edge? How is the setup and hold time measured? As far as I know we take the measurement at 50% of the signal amplitude as shown below. Can you confirm this or correct me, please?

Are there any requirements on the SYNC signal regarding risetime, slewrate? If yes, can you share, please?

Thank you and Best Regards,

Hans

over 2 years ago

0 Noel Fung over 2 years ago

TI__Guru** 112170 points

Hi Hans,

here is the timing diagram.

We didn't specify the rise time of the SYNC signal, but it has to be compatible with the OSCin signal as foscin is usually vey high frequency, if the rise time of SYNC is too long, we cannot meet the setup time requirement.

0 Hans over 2 years ago in reply to Noel Fung

TI__Genius 12865 points

Hi Noel,

so the timing starts/stops at 50% of the signal amplitude, correct? Where can I find the timing diagram (Figure 6-1), please? I cannot find it in the LMX2594 data sheet.

Thanks and Best Regards,

Hans

0 Noel Fung over 2 years ago in reply to Hans

TI__Guru** 112170 points

Hi Hans,

Right, 50%.

This diagram is available in LMX2694 datasheet. We have plan to put this diagram in next revision LMX2594 datasheet.

0 Hans over 2 years ago in reply to Noel Fung

TI__Genius 12865 points

Hi Noel, 2 last questions:

the OSCIN signal shown in Fig. 6-1 is the differential signal OSCIN = OSCIN_P - OSCIN_N?

a SYNC signal risetime of 3ns (10% to 90%) should work for an OSCIN signal of 100MHz to meet the required setup/hold (2.5ns/2.0ns) times ?

Thanks and Best Regards, Hans

0 Noel Fung over 2 years ago in reply to Hans

TI__Guru** 112170 points

Hi Hans,

Righ, the reference is OSCinP pin.

3ns seems long to me. A 100MHz clock period is just 10ns.

See below the clock and sync pulse signals generated from LMK04832, rise time is less than 1ns.

0 Hans over 2 years ago in reply to Noel Fung

TI__Genius 12865 points

Hi Noel,

so OSCIN = OSCINP? That means it is not differential?

Thanks and Best Regards, Hans

+1 Noel Fung over 2 years ago in reply to Hans

TI__Guru** 112170 points

Hi Hans,

Single-ended signal should be connected to the OSCINP pin, and have OSCINN pin AC-shunt to ground. Output of the OSCIN buffer is OSCINP - OSCINN = OSCINP.

For differential signal, OSCINP-OSCINN = 2x OSCINP.

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LMX2594: SYNC Signal requirements