SM320DM6446 datasheet(101/228 Pages) TI1

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6.5.1.2 24-MHz Crystal for USB Oscillator

M24XI

M24XO

M24VSS

M24VDD

Crystal

24 MHz

1.8 V

RBIAS

(optional)

1C2

) C2)

SM320DM6446

Digital Media System-on-Chip

www.ti.com

SPRS607A – JUNE 2009 – REVISED JUNE 2009

In this option, a crystal is used as the external clock input to the DM6446 USB PLL.

The 24-MHz oscillator provides the reference clock for the DM6446 USB peripheral. The on-chip oscillator

requires an external 24-MHz crystal connected across the M24XI and M24XO pins, along with two load

capacitors, as shown in Figure 6-11.The external crystal load capacitors must be connected only to the

24-MHz oscillator ground pin (M24VSS). Do not connect to board ground (VSS).

Figure 6-11. 24-MHz USB Oscillator

The RBIAS resistor is optional. If the RBIAS resistor is used, it should equal 1 M

Ω ±5%. The load

capacitors, C1 and C2, should be chosen such that the equation is satisfied (typical values are C1 = C2 =

10 pF). CL in the equation is the load specified by the crystal manufacturer. All discrete components used

to implement the oscillator circuit should be placed as close as possible to the associated oscillator pins

(M24XI and M24XO) and to the M24XVSS pin.

Table 6-11. Crystal Requirements for a 24-MHz USB Oscillator

PARAMETER

MIN

TYP

MAX

UNIT

Start-up time (from power up until oscillating at stable frequency of 24 MHz)

Oscillation frequency

MHz

ESR

Ω

Frequency stability

±50

ppm

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