USS-820FD
USB Device Controller
Data Sheet, Rev. 1
August 2004
Electrical Characteristics
(continued)
Power Considerations
The USB specification places current limits on bus-powered devices. The limit is tighter for a device that has not
yet been configured. The tightest limit is for a suspended device.
The current values listed in Table 45 for a preconfigured device assume fairly low activity (about 5%) on USB. The
maximum value for a configured device assumes the device is transmitting 80% of the time on USB. All current
values assume a 35 pF load on the package pins.
The limit for suspended devices can only be met if careful measures are taken to control the interface to the USS-
820FD, as documented in the Suspend and Resume Behavior section.
USB Transceiver Driver Characteristics
Table 46. USB Transceiver Driver Characteristics
Parameter
Rise and Fall Times:
(10%—90%)
(90%—10%)
Rise/Fall Time Matching
Crossover Point
Output Impedance*
Symbol
t
R
t
F
t
RFM
V
CRS
Z
DRV
Test Conditions
OEN = 0, C
L
= 50 pF
OEN = 0, C
L
= 50 pF
OEN = 0, C
L
= 50 pF
OEN = 0, C
L
= 50 pF
OEN = 0
Min
4
4
90
1.3
28
Max
20
20
110
2.0
43
Unit
ns
ns
%
V
Ω
* At steady-state drive, when used with an external series resistor of 24
Ω.
48
Agere Systems Inc.
AGERE [ AGERE SYSTEMS ]
