5
IMP5
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Application Information
Figure 1. Receiving Waveform – 20MHz
Figure 2. Driving Waveform – 20MHz
Receiver
1 Meter, AWG 28
IMP5115
Driver
IMP5115
5115_03.eps
Figure 3.
IMP5115 Maximizes Line Current
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 IMP5115 closely repro-
duces the optimum case when the device is enabled. To enable the
device the Disable pin must be driven LOW. When enabled,
quiescent current is 6mA and the device will respond to line
demands by delivering 24mA on assertion and by imposing 2.85V
on de-assertion.
Disable/Sleep Mode
Disable mode places the device in a sleep state, where quiescent
current typically 375µA. 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 IMP5115 are their compatibility with
active negation drivers.
(
V
REF
−
V
LINE
)
=
I.
R
The IMP5115, with its unique new architecture, applies the maxi-
mum amount of current regardless of line voltage until the
termination high threshold (2.85V) is reached.
Table 1. Power Up/ Power Down Function Table
Disable
H
L
Open
Outputs
Enabled
Disabled/High Impedance
Enabled
Quiescent Current
6mA
375
µA
6mA
5115_t04.eps
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© 2000 IMP, Inc.
IMP [ IMP, INC ]
