Si5345-44-42-D-RM
Rev. 1.0
47
7. 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 Figure 21. 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. The OUT9 and FB_IN pins are recommended for the external feedback
connection in the Si5345. OUT3 and FB_IN pins are recommended for the external feedback in the Si5344. OUT1
or OUT2 are recommended with FB_IN in the Si5342. 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.
Figure 21. Si5345 Zero Delay Mode Set-up
Table 32 lists the registers used for the Zero Delay mode.
VDDO7
OUT7
OUT7
÷R
7
OUT0
VDDO0
OUT0
÷R
0
Si5345/44/42
IN0
IN0
IN1
IN1
IN2
IN2
÷P
1
÷P
0
÷P
2
DSPLL
LPF
PD
÷M
15GHz
IN3/FB_IN
÷P
3
10
0
IN3/FB_IN
÷N
0
t
0
÷N
1
t
1
÷N
2
t
2
÷N
3
t
3
÷N
4
t
4
OUT2
VDDO2
OUT2
÷R
2
External Feedback Path
OUT1
VDDO1
OUT1
÷R
1
OUT8
VDDO8
OUT8
÷R
8
OUT9
VDDO9
OUT9
÷R
9