SI5335 Datasheet, PDF (20/47 Pages) Silicon Laboratories – WEB-CUSTOMIZABLE, ANY-FREQUENCY, ANY-OUTPUT QUAD CLOCK GENERATOR/BUFFER

Si5335
values for R₁ and R₂ are calculated to provide a 50 termination to V_DD-2V. Given this, the recommended resistor
values are R₁ = 127 and R₂ = 82.5  for V_DD = 3.3 V, and R₁ = 250 andR₂ = 62.5 for V_DD = 2.5 V.
3.3 V, 2.5 V
LVPECL
Rb
Keep termination close to
input pin of the Si5335
0.1 uF
50
100
0.1 uF
Rb
50
Must be ac coupled
Pin 1
Pin 2
Si5335
VDD= 3.3 V, 2.5 V
LVPECL
LVPECL Input Signal with Source Biasing Option
Keep termination close to
input pin of the Si5335
VDD VDD
R1
R1
0.1 uF
50
Pin 1
Must be ac coupled
Si5335
50
R2
VT = VDD – 2 V
R1 // R2 = 50 Ohm
0.1 uF
R2
Pin 2
LVPECL Input Signal with Load Biasing Option
Figure 6. Recommended Options for Interfacing to an LVPECL Input Signal
Since the differential receiver of the Si5335 is internally self biased, an LVPECL signal may not be dc-coupled to
the device. Figure 7 shows some common LVPECL connections that should not be used because of the dc levels
they present at the receiver’s input.
DC Coupled with
Thevenin Termination
50
50
LVPECL
VDD VDD
R1
R₁
R₂
R2
LVPECL
Rb
AC Coupled with
Thevenin Re-Biasing
VDD VDD
R1
R1
50
50
Rb
R₂
R₂
Not Recommended
Figure 7. Common LVPECL Connections that May be Destructive to the Si5335 Input
20
Rev. 1.4