3.5.12 Zero Delay Mode

A zero delay mode is available for applications that require fixed and consistent minimum delay between the selected input and outputs.

The zero delay mode is configured by opening the internal feedback loop through software configuration and closing the loop externally

as shown in the figure below. This helps to cancel out the internal delay introduced by the dividers, the crosspoint, the input, and the

output drivers. Any one of the outputs can be fed back to the FB_IN pins, although using the output driver that achieves the shortest

trace length will help to minimize the input-to-output delay. It is recommended to connect OUT9 (Si5341) or OUT3 (Si5340) to FB_IN for

external feedback. The FB_IN input pins must be terminated and ac-coupled when zero delay mode is used. A differential external

feedback path connection is necessary for best performance.

Zero Delay

Mode

Si5341

IN_SEL[1:0]

IN0

IN0b

IN1

IN1b

IN2

IN2b

OUT0b

VDDO0

OUT0

OUT2b

VDDO2

OUT2

OUT3b

VDDO3

OUT3

OUT7b

VDDO7

OUT7

OUT8b

VDDO8

OUT8

OUT9b

VDDO9

OUT9

OUT1b

VDDO1

OUT1

MultiSynth

& Dividers

FB_IN

FB_INb

External Feedback Path

PD

LPF

÷

÷

PLL

Figure 3.8. Si5341 Zero Delay Mode Setup

3.5.13 Sync Pin (Synchronizing R Dividers)

All the output R dividers are reset to the default NVM register state after a power-up or a hard reset. This ensures consistent and re-

peatable phase alignment across all output drivers to within ±100 ps of the expected value from the NVM download. Resetting the de-

vice using the RSTb pin or asserting the hard reset bit will have the same result. The SYNCb pin provides another method of re-aligning

the R dividers without resetting the device, however, the outputs will only align to within 50 ns when using the SYNCb pin. This pin is

positive edge triggered. Asserting the sync register bit provides the same function as the SYNCb pin. A soft reset will align the outputs

to within ±100 ps of the expected value based upon the Nx_DELAY parameter.

3.5.14 Output Crosspoint

The output crosspoint allows any of the N dividers to connect to any of the clock outputs.

Si5341/40 Rev D Data Sheet

Functional Description

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