IMP5
IMP5225
1 1 1/51 1 2
Application Information
Figure 1. Receiving Waveform – 20MHz
Receiver
DISCONNECT 1
IMP5225
DISCONNECT 2
1 Meter, AWG 28
Figure 2. Driving Waveform – 20MHz
Driver
DISCONNECT 1
IMP5225
DISCONNECT 2
5225_03.eps
Figure 3.
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 IMP5225 closely repro-
duces the optimum case when the device is enabled. To enable
the device the DISC1 and DISC2 pins are pulled HIGH. 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 DISC1 and DISC2 pins must be
driven LOW. 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.
An additional feature of the IMP5225 is its compatibility with
active negation drivers.
(
V
REF
−
V
LINE
)
=
I.
R
The IMP5225, 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.
Table 1. Power Up/ Power Down Function Table
DISCONNECT 1
H
H
L
L
Open
DISCONNECT 2
H
L
H
L
Open
Outputs
Disabled
Enabled
Enabled
Disabled
Disabled
Maximum Quiescent
Current
15mA
15mA
15mA
150µA
150µA
5225_t04.eps
4
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© 2000 IMP, Inc.
A1PROS [ A1 PROS CO., LTD. ]
