4.6.2 LVCMOS Output Impedance and Drive Strength Selection
Each LVCMOS driver has a configurable output impedance to accommodate different trace impedances and drive strengths. A series
source termination resistor (Rs) is recommended close to the output to match the selected output impedance to the trace impedance
(i.e. Rs = Trace Impedance – Zs). There are multiple programmable output impedance selections for each VDDO option as shown in
the following table. Generally, the lowest impedance for a given supply voltage is preferable, since it will give the fastest edge rates.
Table 4.8. LVCMOS Output Impedance and Drive Strength Selections
VDDO
OUTx_CMOS_DRV
Driver Impedance (Zs)
Drive Strength (Iol/Ioh)
3.3 V
0x1
38 Ω
10 mA
0x2
30 Ω
12 mA
0x3
1
22 Ω
17 mA
2.5 V
0x1
43 Ω
6 mA
0x2
35 Ω
8 mA
0x3
1
24 Ω
11 mA
1.8 V
0x3
1
31 Ω
5 mA
Note:
1. Use of the lowest impedance setting is recommended for all supply voltages.
Table 4.9. LVCMOS Drive Strength Registers
Register Name
Hex Address
[Bit Field]
Function
OUT0A_CMOS_DRV
0x0104[7:6]
LVCMOS output impedance. See the table
above for settings.
OUT0_CMOS_DRV
0x0109[7:6]
OUT1_ CMOS_DRV
0x010E[7:6]
OUT2_ CMOS_DRV
0x0113[7:6]
OUT3_ CMOS_DRV
0x0118[7:6]
OUT4_ CMOS_DRV
0x011D[7:6]
OUT5_ CMOS_DRV
0x0122[7:6]
OUT6_ CMOS_DRV
0x0127[7:6]
OUT7_ CMOS_DRV
0x012C[7:6]
OUT8_ CMOS_DRV
0x0131[7:6]
OUT9_ CMOS_DRV
0x0136[7:6]
OUT9A_ CMOS_DRV
0x013B[7:6]
4.6.3 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. Each output driver automatically detects the voltage
on the VDDO pin to properly determine the correct output voltage.
Si5386 Rev. E Reference Manual • Output Clocks
Skyworks Solutions, Inc. • Phone [781] 376-3000 • Fax [781] 376-3100 • [email protected] • www.skyworksinc.com
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Rev. 1.2 • Skyworks Proprietary Information • Products and Product Information are Subject to Change Without Notice • December 9, 2021
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