TUSB1310A datasheet(30/42 Pages) TI

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VDDO1P1

VSSOSC

VDDO1P8

VSSO

CL1

Crystal

VDD1P8

CL2

VDD1P1

TUSB1310A

SLLSE32D

– NOVEMBER 2010 – REVISED MAY 2011

www.ti.com

Load capacitance (CLOAD) of the crystal varying with the crystal vendors is the total capacitance value of

the entire oscillation circuit system as seen from the crystal. It includes two external capacitors CL1 and

CL2 in Figure 5-4. The trace length between the decoupling capacitors and the corresponding power pins

on the TUSB1310A needs to be minimized. It is also recommended that the trace length from the

capacitor pad to the power or ground plane be minimized.

Figure 5-4. Typical Crystal Connections

5.2

Clock Source Requirements

5.2.1

Clock Source Selection Guide

Reference clock jitter is an important parameter. Jitter on the reference clock will degrade both the

transmit eye and receiver jitter tolerance no matter how clean the rest of the PLL is, thereby impairing

system performance. Additionally, a particularly jittery reference clock may interfere with PLL lock

detection mechanism, forcing the Lock Detector to issue an Unlock signal. A good quality, low jitter

reference clock is required to achieve compliance with supported USB3.0 standards. For example,

USB3.0 specification requires the random jitter (RJ) component of either RX or TX to be 2.42 ps (random

phase jitter calculated after applying jitter transfer function - JTF). As the PLL typically has a number of

additional jitter components, the Reference Clock jitter must be considerably below the overall jitter

budget.

5.2.2

Oscillator

If an external clock source is used, XI should be tied to the clock source and XO should be left floating.

Table 5-1. Oscillator Specification

PARAMETER

MIN

TYP

MAX

UNITS

CONDITION

Frequency tolerance

±50

ppm

Operational temperature

Frequency stability

±50

ppm

1 year aging

Rise/Fall time

nsec

20% - 80%

Reference clock RJ

0.8

psec

with JTF (1 sigma)(1)(2)

(1)

Sigma value assuming Gaussian distribution

(2)

After application of JTF

DESIGN GUIDELINES

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