Intel manual Crystal and Crystal Oscillator Connections, 21143 External Component Connections

Intel® 21143 PCI/CardBus 10/100Mb/s Ethernet LAN Controller

Figure 10. 21143 External Component Connections

Intel®	21143
Ethernet Controller
Crystal	xtal1	106
				82 pF
Connection			10 kΩ
	xtal2	105	100 Ω	120 pF	GND
Crystal	xtal1	106	20-MHz Input Clock
Oscillator		107	No Connection
Connection	xtal2
	iref	108
Current			2.4 kΩ
Reference
Connection			GND
	vcap_h	110
				0.022 µF
				GND

20-MHz Crystal

B0033-01

4.3Crystal and Crystal Oscillator Connections

Figure 10 shows two serial clock connections; select either the crystal connection or the crystal oscillator connection. According to the IEEE 802.3 standard, a 20 MHz crystal is required. The crystal frequency must not vary by more than 100 parts per million (PPM), or 0.01%. Place the crystal as close as possible to the 21143.

Because the frequency of crystals from different vendors can vary, test the crystals in the actual circuit. It may be necessary to vary the tuning of the surrounding components. However, after the capacitors have been tuned for the specific crystal, the design does not need to be altered on a board-by-board basis.

The 21143 also supports a crystal oscillator (Figure 10). This configuration requires no external component and xtal2 should be left open.This is useful for applications with multiple network connections.

Table 12 lists the crystal specifications.

Table 12. Crystal Specifications

Specification	Value	Units
Crystal frequency	20.000	MHz
Frequency tolerance	±50	PPM
Load capacitance	50	pF
Frequency stability	±30	PPM
Maximum effective series resistance	40	Ohms (Ω)
Test condition drive level	100	µW

20 Design Guide