FUJITSU MB91401 User Manual
Page 64
MB91401
64
(9) USB interface
*1 : The AC characteristics of the USB interface conform to USB Specification Revision 1.1.
*2 :
<
Driver Characteristics TFR, TFF, TFRFM>
These items specify the differential data signal rise (trise) and fall (tfall) times.
These are defined as the times between 10
%
to 90
%
of the output signal voltage.
For the full-speed buffer, trise and tfall are specified such that the tr/tf ratio falls within
±
10
%
to minimize RFI
radiation.
*3 :
USB full-speed connection is performed via a shielded twisted-pair cable at a characteristic impedance of
90
Ω
±
15
%
. The USB Standard stipulates that the USB driver’s output impedance must be within the range
of 28
Ω
to 44
Ω
. The USB Standard also stipulates that a discrete serial resistor (R
S
) must be added to have
balance while satisfying the above standard.
The output impedance of the USB I/O buffer on this LSI is about 3
Ω
to 19
Ω
. Serial resistor R
S
to be added
must be 25
Ω
to 30
Ω
(27
Ω
recommended) .
Capacitor CL of 50 pF must be added as well.
Parameter
Symbol
Pin
Value
Unit
Remarks
Min
Typ
Max
Input clock
tucyc
UCLK48
48*
1
MHz 2500ppm accuracy*
1
RISE Time
tutfr
UDP, UDM
4
20
ns
*2
Fall Time
tutff
UDP, UDM
4
20
ns
*2
Differential Rise and Fall
Timing Matching
tutfrfm
UDP, UDM
90
111.11
%
*2
Driver Output Resistance
tzdrv
UDP, UDM
28
44
Ω
*3
UCLK48
tucyc
10%
10%
90%
90%
tutff
tutfr
UDP
UDM
Prelminary
2004.11.12