LAN8720A-CP-TR SMSC, LAN8720A-CP-TR Datasheet - Page 34

• Manufacturer Part Number: LAN8720A-CP-TR
• Description: Ethernet ICs RMII 10/100 ETH XCVR w/HP AutoMDIXSupport
• Manufacturer: SMSC

Specifications of LAN8720A-CP-TR

• Product: Ethernet Transceivers
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Revision 1.2 (11-10-10)
3.7.4.1
3.7.4.2
Reference
50MHz
Clock
Accepts external
REF_CLK
REF_CLK In Mode
In REF_CLK In Mode, the 50MHz REF_CLK is driven on the XTAL1/CLKIN pin. A 50MHz source for
REF_CLK must be available external to the device when using this mode. The clock is driven to both
the MAC and PHY as shown in
REF_CLK Out Mode
To reduce BOM cost, the device includes a feature to generate the RMII REF_CLK signal from a low-
cost, 25MHz fundamental crystal. This type of crystal is inexpensive in comparison to 3
crystals that would normally be required for 50MHz. The MAC must be capable of operating with an
external clock to take advantage of this feature as shown in
In order to optimize package size and cost, the REFCLKO pin is multiplexed with the nINT pin. In
REF_CLK Out mode, the nINT functionality is disabled to accommodate usage of REFCLKO as a
50MHz clock to the MAC.
Note: The REF_CLK Out Mode is not part of the RMII Specification. Timing in this mode is not
50MHz clock
MAC
compliant with the RMII specification. To ensure proper system operation, a timing analysis of
the MAC and LAN8720 must be performed.
Interface
RMII
Figure 3.7 External 50MHz clock sources the REF_CLK
2
2
2
Figure
DATASHEET
nINT
MDIO
MDC
TXD[1:0]
TXEN
RXD[1:0]
CRS_DV
RXER
LED[2:1]
nRST
LAN8720A/LAN8720Ai
3.7.
34
10/100 PHY
24-QFN
RMII
Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support
XTAL1/CLKIN
XTAL2
RXP
RXN
Figure
TXN
TXP
3.8.
SMSC LAN8720A/LAN8720Ai
Mag
All RMII signals are
synchronous to the supplied
clock
rd
Datasheet
RJ45
overtone