
SMSC DS – LPC47M14X
Page 178
Rev. 03/19/2001
t 3
V c c
A ll H o s t
A c c e s s e s
t 2
t 1
FIGURE 9 – POWER-UP TIMING
NAME
DESCRIPTION
MIN
TYP
MAX
UNITS
t1
Vcc Slew from 2.7V to 0V
300
μ
s
t2
Vcc Slew from 0V to 2.7V
100
μ
s
t3
All Host Accesses After Powerup (Note 1)
125
500
μ
s
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 (C
IND
). 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)
SYM
(NOTES 1, 2, 3)
PARAMETER
DRIVER
CHARACTERISTICS:
DRIVER CHARACTERISTICS (Full-Speed)
Transition Time:
Rise Time
Fall Time
CONDITIONS
MIN
MAX
UNIT
TR
TF
Note 4,5 and FIGURE 10
& FIGURE 11
CL = 50 pF
CL = 50 pF
4
4
20
20
ns
ns