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LAN8720AI 参数 Datasheet PDF下载

LAN8720AI图片预览
型号: LAN8720AI
PDF下载: 下载PDF文件 查看货源
内容描述: 小尺寸RMII 10/100以太网收发器, HP Auto-MDIX的支持 [Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support]
分类和应用: 以太网局域网(LAN)标准
文件页数/大小: 79 页 / 1119 K
品牌: SMSC [ SMSC CORPORATION ]
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Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support  
Datasheet  
3.7.4.1  
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 Figure 3.7.  
LAN8720A/LAN8720Ai  
10/100 PHY  
24-QFN  
RMII  
MAC  
RMII  
MDIO  
MDC  
nINT  
Accepts external  
50MHz clock  
Mag  
RJ45  
TXD[1:0]  
TXP  
TXN  
2
2
TXEN  
RXP  
RXN  
RXD[1:0]  
CRS_DV  
RXER  
REF_CLK  
All RMII signals are  
synchronous to the supplied  
clock  
XTAL1/CLKIN  
XTAL2  
LED[2:1]  
nRST  
2
Interface  
50MHz  
Reference  
Clock  
Figure 3.7 External 50MHz clock sources the REF_CLK  
REF_CLK Out Mode  
3.7.4.2  
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 3rd overtone  
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 Figure 3.8.  
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  
compliant with the RMII specification. To ensure proper system operation, a timing analysis of  
the MAC and LAN8720 must be performed.  
Revision 1.4 (08-23-12)  
34  
SMSC LAN8720A/LAN8720Ai  
DATASHEET