Datasheet

Application Information

13−1

SLLS535E − April 2008 TUSB6250

13 Application Information

13.1 Crystal Selection and Reference Circuitry

The TUSB6250 is designed to use an external 24-MHz crystal connected between the XTAL1 and XTAL2 pins

to provide the reference for an internal oscillator circuit. The oscillator, in turn, drives a PLL circuit that

generates the various clocks required for transmission and resynchronization of data at the full-speed and

high-speed data rates.

The following are some typical specifications for crystals that can be used in order to achieve the required

frequency, accuracy, and stability.

• Frequency: 24 MHz

• Crystal mode of operation: fundamental

• Crystal circuit type: parallel resonant

• Frequency tolerance: ±50 ppm (maximum: ±100 ppm)

• Frequency stability: ±50 ppm (maximum: ±100 ppm)

• Aging (long term stability): ±5 ppm per year

• Maximum equivalent series resistance (ESR): 50 Ω (100 Ω, if C

and C

< 10 pF).

The C

and C

are the load capacitors to be used for fundamental parallel resonant crystal circuitry. They

should be of equal value for optimum symmetry. See the Selection and Specification of Crystals for Texas

Instruments USB 2.0 Devices application note (SLLA122) for detailed information.