IMP51IM11P/55121129
Application Information
Figure 1. Receiving Waveform – 20MHz
Figure 2. Driving Waveform – 20MHz
Receiver
Driver
1 Meter, AWG 28
IMP5219
IMP5219
5219_03.eps
Figure 3.
IMP5219 Maximizes Line Current
Disable/ Sleep Mode
Cable transmission theory suggests to optimize signal speed and Disable mode places the device in a sleep state, where quiescent
quality, the termination should act both as an ideal voltage refer- current typically 375µA. When disabled, all outputs are in a high
ence when the line is released (deasserted) and as an ideal impedance state and output capacitance is a low 3pF. Sleep mode
current source when the line is active (asserted). Common active can be used for power conservation or to remove the terminator
terminators which consist of linear regulators in series with resis- from the SCSI chain.
tors (typically 110Ω) are a compromise. With coventional linear
An additional feature of the IMP5219 is its compatibility with
terminators as the line voltage increases the amount of current
active negation drivers.
decreases linearly by the equation;
Table 1. Power Up/ Power Down Function Table
V
REF − V
(
)
= I.
LINE
R
Disable
Outputs
Quiescent Current
The IMP5219, 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.
H
Enabled
6mA
Disable/High
Impedance
L
375µA
Acting as a near ideal line terminator, the IMP5219 closely repro-
duces the optimum case when the device is enabled. To enable the
device the Disable pin must be driven HIGH or left Open. 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.
Open
Enabled
6mA
5219_t04.eps
4
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