IMP5226
1
Application Information
Cable transmission theory suggests to optimize signal speed and
quality, the termination should act both as an ideal voltage refer-
ence when the line is released (deasserted) and as an ideal
current source when the line is active (asserted). Common active
terminators which consist of linear regulators in series with resis-
tors (typically 110Ω) are a compromise. With coventional linear
terminators as the line voltage increases the amount of current
decreases linearly by the equation;
Acting as a near ideal line terminator, the IMP5226 closely repro-
duces the optimum case when the device is enabled. To enable
the device the disconnect pin is pulled LOW. During this mode
of operation, quiescent current is 10mA, and the device will
respond to line demands by delivering 24mA on assertion and by
imposing 2.85V on deassertion.
In order to disable the device, the disconnect pin must be driven
HIGH In the disable mode, the device is in a sleep state with
quiescent current less than 150µA. When disabled, all
outputs are in a high impedance state. Sleep mode can be used
for power conservation or to remove the terminator from the
SCSI chain.
V
REF − V
(
)
= I.
LINE
R
The IMP5226, with its unique new architecture, applies the max-
imum amount of current regardless of line voltage until the
termination high threshold (2.85V) is reached.
An additional feature of the IMP5226 is its compatibility with
active negation drivers.
Table 1. Power Up/ Power Down Function Table
Maximum Quiescent
DISCONNECT Outputs
Current
L
Enabled
15mA
150µA
150µA
H
HI Z
Open
HI Z
5226_t04.eps
© 2000 IMP, Inc.
Data Communications
5
A1PROS [ A1 PROS CO., LTD. ]
