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SMSC LAN8720, LAN8720i 6.6Clock Circuit, MIN, NOM, MAX, Note, Note, Note, Note, Note, Note, UNITS, NOTES, SYMBOL, PARAMETER, Table 6.12 LAN8720/LAN8720i Crystal Specifications

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Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIX Support

Datasheet

6.6Clock Circuit

LAN8720/LAN8720i can accept either a 25MHz crystal or a 25MHz single-ended clock oscillator (±50ppm) input. If the single-ended clock oscillator method is implemented, XTAL2 should be left unconnected and XTAL1/CLKIN should be driven with a nominal 0-3.3V clock signal. See Table 6.12 for the recommended crystal specifications.

Table 6.12 LAN8720/LAN8720i Crystal Specifications

PARAMETER	SYMBOL	MIN	NOM		MAX	UNITS	NOTES

Crystal Cut			AT, typ

Crystal Oscillation Mode		Fundamental Mode

Crystal Calibration Mode		Parallel Resonant Mode

Frequency	Ffund	-	25.000		-	MHz
Frequency Tolerance @ 25oC	Ftol	-	-		±50	PPM	Note 6.1
Frequency Stability Over Temp	Ftemp	-	-		±50	PPM	Note 6.1
Frequency Deviation Over Time	Fage	-	+/-3 to 5		-	PPM	Note 6.2
Total Allowable PPM Budget		-	-		±50	PPM	Note 6.3

Shunt Capacitance	CO	-	7 typ		-	pF
Load Capacitance	CL	-	20 typ		-	pF
Drive Level	PW	300	-		-	uW
Equivalent Series Resistance	R1	-	-		30	Ohm
Operating Temperature Range		Note 6.4	-		Note 6.5	oC
LAN8720/LAN8720i		-	3 typ		-	pF	Note 6.6
XTAL1/CLKIN Pin Capacitance

LAN8720/LAN8720i XTAL2 Pin		-	3 typ		-	pF	Note 6.6
Capacitance

Note 6.1 The maximum allowable values for Frequency Tolerance and Frequency Stability are application dependant. Since any particular application must meet the IEEE ±50 PPM Total PPM Budget, the combination of these two values must be approximately ±45 PPM (allowing for aging).

Note 6.2 Frequency Deviation Over Time is also referred to as Aging.

Note 6.3 The total deviation for the Transmitter Clock Frequency is specified by IEEE 802.3u as ±100 PPM.

Note 6.4 0oC for extended commercial version, -40oC for industrial version.

Note 6.5 +85oC for extended commercial version, +85oC for industrial version.

Note 6.6 This number includes the pad, the bond wire and the lead frame. PCB capacitance is not included in this value. The XTAL1/CLKIN pin, XTAL2 pin and PCB capacitance values are required to accurately calculate the value of the two external load capacitors. The total load capacitance must be equivalent to what the crystal expects to see in the circuit so that the crystal oscillator will operate at 25.000 MHz.

SMSC LAN8720/LAN8720i	65	Revision 1.0 (05-28-09)
	DATASHEET

Contents

LAN8720/LAN8720i Small Footprint RMII 10/100 Ethernet Transceiver with HP Auto-MDIXSupport PRODUCT FEATURES DATASHEET Table of Contents Page Page List of Figures List of Tables Page Chapter 1 Introduction 1.1General Terms and Conventions 1.2General Description RJ45 Crystal or 1.3Architectural Overview 1.3.1Configuration Figure 1.2 LAN8720/LAN8720i Architectural Overview Chapter 2 Pin Configuration 2.1Package Pin-outDiagram and Signal Table Table 2.1 LAN8720/LAN8720i 24-PINQFN Pinout PIN NO PIN NAME Chapter 3 Pin Description 3.1MAC Interface Signals 3.2LED Signals 3.3Management Signals 3.4General Signals 3.510/100 Line Interface Signals 3.6Analog Reference 3.7Power Signals Chapter 4 Architecture Details 4.1Top Level Functional Architecture 4.2100Base-TXTransmit 4.2.1100M Transmit Data Across the MII/RMII Interface 4.2.24B/5B Encoding 4.2.3Scrambling 4.2.4NRZI and MLT3 Encoding 4.2.5100M Transmit Driver 4.2.6100M Phase Lock Loop (PLL) 4.3100Base-TXReceive 4.3.1100M Receive Input 4.3.2Equalizer, Baseline Wander Correction and Clock and Data Recovery 4.3.3NRZI and MLT-3Decoding 4.3.4Descrambling 4.3.5Alignment 4.3.65B/4B Decoding 4.3.7Receive Data Valid Signal 4.410Base-TTransmit 4.4.110M Transmit Data Across the MII/RMII Interface 4.4.2Manchester Encoding 4.4.310M Transmit Drivers 4.510Base-TReceive 4.5.110M Receive Input and Squelch 4.5.2Manchester Decoding 4.5.310M Receive Data Across the MII/RMII Interface 4.5.4Jabber Detection 4.6MAC Interface 4.6.1RMII 4.7Reference Clock 4.7.1REF_CLK In Mode 4.7.2REF_CLK OUT Mode MAC RMII 10/100 PHY Mag Figure 4.5 LAN8720 sources REF_CLK from a 25MHz crystal 4.8Auto-negotiation Page 4.8.1Parallel Detection 4.8.2Re-starting Auto-negotiation 4.8.3Disabling Auto-negotiation 4.8.4Half vs. Full Duplex 4.9HP Auto-MDIXSupport 4.10nINTSEL Strapping and LED Polarity Selection 4.11REGOFF and LED Polarity Selection 4.12PHY Address Strapping 4.13Variable Voltage I/O 4.14Transceiver Management Control 4.14.1Serial Management Interface (SMI) Figure 4.10 MDIO Timing and Frame Structure - READ Cycle Figure 4.11 MDIO Timing and Frame Structure - WRITE Cycle Chapter 5 SMI Register Mapping Page Page Page 5.1SMI Register Format Table 5.21 Register 0 - Basic Control ADDRESS DEFAULT Table 5.22 Register 1 - Basic Status Table 5.22 Register 1 - Basic Status (continued) Table 5.23 Register 2 - PHY Identifier Table 5.24 Register 3 - PHY Identifier Table 5.25 Register 4 - Auto Negotiation Advertisement Table 5.25 Register 4 - Auto Negotiation Advertisement (continued) Register 5 - Auto Negotiation Link Partner Ability Table 5.27 Register 6 - Auto Negotiation Expansion Table 5.28 Register 16 - Silicon Revision Table 5.29 Register 17 - Mode Control/Status Table 5.29 Register 17 - Mode Control/Status (continued) Table 5.30 Register 18 - Special Modes Table 5.31 Register 26 - Symbol Error Counter Register 27 - Special Control/Status Indications Register 28 - Special Internal Testability Controls Table 5.34 Register 29 - Interrupt Source Flags Table 5.34 Register 29 - Interrupt Source Flags (continued) Table 5.35 Register 30 - Interrupt Mask Table 5.36 Register 31 - PHY Special Control/Status 5.2Interrupt Management 5.2.1Primary Interrupt System 5.2.2Alternate Interrupt System 5.3Miscellaneous Functions 5.3.1Carrier Sense 5.3.2Collision Detect 5.3.3Isolate Mode 5.3.4Link Integrity Test 5.3.5Power-Downmodes 5.3.6Reset 5.3.7LED Description 5.3.8Loopback Operation XFMR Digital Ethernet Transceiver 10/100 TXD X Digital 5.3.9Configuration Signals Table 5.39 MODE[2:0] Bus DEFAULT REGISTER BIT VALUES MODE[2:0] MODE DEFINITIONS REGISTER Chapter 6 AC Electrical Characteristics 6.1Serial Management Interface (SMI) Timing 6.2RMII 10/100Base-TX/RXTimings (50MHz REF_CLK IN) 6.2.1RMII 100Base-TTX/RX Timings (50MHz REF_CLK IN) CLKIN TXD[1:0] Page Page 6.3RMII 10/100Base-TX/RXTimings (50MHz REF_CLK OUT) 6.3.1RMII 100Base-TTX/RX Timings (50MHz REF_CLK OUT) 6.3.1.2100M RMII Transmit Timing (50MHz REF_CLK OUT) TXD[1:0] Page 6.4RMII CLKIN Requirements 6.5Reset Timing 6.6Clock Circuit Chapter 7 DC Electrical Characteristics 7.1DC Characteristics 7.1.1Maximum Guaranteed Ratings 7.1.2Operating Conditions 7.1.3Power Consumption Table 7.4 Power Consumption Device Only (REF_CLK IN MODE) VDDA3.3 TOTAL POWER CURRENT Page 7.1.4DC Characteristics - Input and Output Buffers Table 7.7 LAN Interface Signals Table 7.8 LED Signals Table 7.9 Configuration Inputs Table 7.10 General Signals Internal Pull-Up / Pull-DownConfigurations Internal Pull-Up / Pull-DownConfigurations (continued) Table 7.12 100Base-TXTransceiver Characteristics Table 7.13 10BASE-TTransceiver Characteristics Chapter 8 Application Notes 8.1Application Diagram 8.1.1RMII Diagram 8.1.2Power Supply Diagram 8.1.3Twisted-PairInterface Diagram 8.2Magnetics Selection Chapter 9 Package Outline Figure 9.1 QFN, 4x4 Taping Dimensions and Part Orientation Figure 9.2 Reel Dimensions Chapter 10 Revision History