LPC47M14X datasheet(178/205 Pages) SMSC

178 / 205 page

SMSC DS – LPC47M14X

Page 178

Rev. 03/19/2001

Vc c

Al l H o s t

A cce s s e s

FIGURE 9 – POWER-UP TIMING

NAME

DESCRIPTION

MIN

TYP

MAX

UNITS

Vcc Slew from 2.7V to 0V

300

µs

Vcc Slew from 0V to 2.7V

100

µs

All Host Accesses After Powerup (Note 1)

125

500

µs

Note 1: Internal write-protection period after Vcc passes 2.7 volts on power-up

USB Hub Interface Timing

The USB Hub uses a differential output driver to drive the USB data signal onto the USB cable. The output rise time

and fall times are measured between 10% and 90% of the signal (see FIGURE 10). Rise and fall time requirements

apply to differential transitions as well as to transitions between differential and single-ended signaling.

The rise and fall times for full-speed buffers are much more stringent than that of low speed buffers. These values,

listed in Table 77, are measured with a load of 50pF and are matched to within

±10% to minimize RFI emissions and

signal skew.

The rise and fall times for low-speed buffers are measure with the loads shown in FIGURE 12. A downstream port is

allowed 150pF of input/output capacitance (CIND). A low-speed device (including cable) may have a capacitance of

as little as 200pF and as much as 450pF. This gives a range of 200pF to 600pF as the capacitive load that the

downstream low-speed buffer must support. Upstream buffers on low-speed devices must be designed to drive the

capacitance of the attached cable plus an additional 150pF. In all cases, the edges must be matched to within

±20%

to minimize RFI emissions and signal skew.

Table 77 – Electrical Source Characteristics

The values listed below satisfy speeds up to 12Mbps (Full Speed)

PARAMETER

SYM

CONDITIONS

(NOTES 1, 2, 3)

MIN

MAX

UNIT

DRIVER

CHARACTERISTICS:

DRIVER CHARACTERISTICS (Full-Speed)

Transition Time:

Rise Time

Fall Time

Note 4,5 and FIGURE 10

& FIGURE 11

CL = 50 pF

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