Skyworks Si5341 - LVCMOS Output Impedance and Drive Strength Selection; LVCMOS Output Signal Swing

5.3.5 LVCMOS Output Impedance and Drive Strength Selection
Each LVCMOS driver has a configurable output impedance to accommodate different trace impedances and drive strengths. A source
termination resistor (Rs) is highly recommended to help match the selected output impedance to the trace impedance (i.e. Rs ~= Trace
Impedance – Zs). For the best signal integrity, Silicon Labs strongly recommends using the setting that produces the lowest source
impedance and then choosing the proper external source resistor to produce the best signal shape at the end of the signal trace.
VDDO
OUTx_CMOS_DRV
Value Setting
Source Impedance (Z
S
)
3.3 V
0x01 38 Ω
0x02 30 Ω
0x03
1
22 Ω
2.5 V
0x01 43 Ω
0x02 35 Ω
0x03
1
24 Ω
1.8 V
0x02 46 Ω
0x03
1
31 Ω
Note:
1. This setting is strongly recommended.
Table 5.5. LVCMOS Drive Strength Control Registers
Setting Name
Hex Address [Bit Field]
Function
Si5341 Si5340
OUT0_CMOS_DRV
OUT1_CMOS_DRV
OUT2_CMOS_DRV
OUT3_CMOS_DRV
OUT4_CMOS_DRV
OUT5_CMOS_DRV
OUT6_CMOS_DRV
OUT7_CMOS_DRV
OUT8_CMOS_DRV
OUT9_CMOS_DRV
0109[7:6]
010E[7:6]
0113[7:6]
0118[7:6]
011D[7:6]
0122[7:6]
0127[7:6]
012C[7:6]
0131[7:6]
013B[7:6]
0113[7:6]
0118[7:6]
0127[7:6]
012C[7:6]
—
—
—
—
—
—
LVCMOS output impedance. See previous table.
5.3.6 LVCMOS Output Signal Swing
The signal swing (V
OL
/V
OH
) of the LVCMOS output drivers is set by the voltage on the VDDO pins. Each output driver has its own
VDDO pin allowing a unique output voltage swing for each of the LVCMOS drivers.
Si5341, Si5340 Rev D Family Reference Manual • Output Clocks
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • sales@skyworksinc.com • www.skyworksinc.com
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