lan8720 Standard Microsystems Corp., lan8720 Datasheet - Page 27

• Manufacturer Part Number: lan8720
• Description: Small Footprint Rmii 10/100 Ethernet Transceiver With Hp Auto-mdix Support
• Manufacturer: Standard Microsystems Corp.

Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support
Datasheet
SMSC LAN8720/LAN8720i
4.7.1
4.7.2
Reference
50MHz
Clock
Accepts external
REF_CLK
REF_CLK In Mode
A 50MHz source of REF_CLK must be available external to the LAN8720 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 LAN8720 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
The LAN8720 is a small size, low pin count device. In order to optimize package size and cost, the
REFCLKO pin is multiplexed with the nINT pin. Therefore, in this specific mode of operation, the nINT
pin is disabled since REFCLKO is used to provide the 50MHz clock to the MAC.
50MHz clock
MAC
Interface
RMII
Figure 4.4 External 50MHz clock sources the REF_CLK
2
2
2
MDIO
MDC
nINT
TXD[1:0]
TXEN
RXD[1:0]
CRS_DV
RXER
LED[2:1]
nRST
DATASHEET
27
10/100 PHY
LAN8720
24-QFN
RMII
XTAL1/CLKIN
Figure
XTAL2
RXP
RXN
TXN
TXP
Figure
4.4.
4.5.
Mag
All RMII signals are
synchronous to the supplied
clock
Revision 1.0 (04-15-09)
rd
RJ45
overtone