IMP51 1 1/51 1 2
Application Information
Figure 1. Receiving Waveform – 20MHz
Receiver
1 Meter, AWG 28
Figure 2. Driving Waveform – 20MHz
Driver
IMP5111
IMP5112
IMP5111
IMP5112
5111/5112_03.eps
Figure 3.
IMP5111/IMP5112 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;
Disable /Sleep Mode
The IMP5111 has an active LOW disconnect pin, and the IMP5112
has an active HIGH disconnect pin. The disable mode is entered
if the disconnect pin on either device is left open.
When disabled the termination lines are in a high impedance
state, and the power supply current drops to 275µA typically. The
disable mode can be used to save power or completely eliminate
the terminator from the SCSI bus.
Disabled terminators appear as distributed capacitance on the
bus. The IMP5111/5112 have been optimized to have only 3pF of
capacitance per output when in the disabled mode.
The IMP5111/5112 are compatible with active negation drivers.
The devices will handle up to 60mA of sink current for drivers
which exceed the 2.85V output high level
.
(
V
REF
−
V
LINE
)
=
I.
R
The IMP5111/5112, with their unique architecture, applies the
maximum amount of current regardless of line voltage until the
termination high threshold (2.85V) is reached.
Table 1. Power Up/ Power Down Function Table
IMP5111
DISCONNECT
H
L
Open
IMP5112
DISCONNECT
L
H
Open
Outputs
Enabled
Disabled/High Impedance
Disabled/High Impedance
Quiescent Current
6mA
275
µA
275
µA
5111/5112_t04a.eps
4
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