Cirrus Logic CS8900A - Manual (Page 121)

DS271F5 121
CS8900A
Crystal LAN™ Ethernet Controller
CIRRUS LOGIC PRODUCT DATASHEET
7.5 10BASE-T WIRING
• If a center tap transformer is used on the RXD+ and RXD- inputs, replace the pair of Rr re-
sistors with a single 2xRr resistor.
• The Rt and Rr resistors are ±1% tolerance.
• The CS8900A supports 100, 120, and 150
Ω unshielded twisted pair cables. The proper val-
ues of Rt and Rr, for a given cable impedance, are shown below:
• Note: for 3.3V operation the turns ratio on TXD+ and TXD- is 1:2.5, rt is 8 Ω for 100 Ω cable
and the 68pF cap changes to 560pF.
Cable Impedance ( Ω) Rt ( Ω) Rr ( Ω)
100 24.3 49.9
120 30.1 60.4
150 37.4 75
Rt
Rt
CS8900A
TD +
TD -
TXD +
TXD -
1 : 2
RJ45
1
2
1 : 1
RD +
RD -
3
6
0.01 μ F
+
RXD+
RXD-
Rr
Rr
0.01
μ F
-
68 pF