lx5218 Microsemi Corporation, lx5218 Datasheet - Page 4

• Manufacturer Part Number: lx5218
• Description: 9-channel Plug And Play Scs I Terminator
• Manufacturer: Microsemi Corporation

LX5218
4
Cable transmission theory suggests to optimize signal speed
and quality, the termination should act both as an ideal voltage
reference 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 resistors (typically
110 ), are a compromise. As the
line voltage increases, the amount
of current decreases linearly by the
equation V = I * R. The LX5218,
with its unique new architecture
applies the maximum amount of
current regardless of line voltage
until the termination high thresh-
old (2.85V) is reached.
minator, the LX5218 closely reproduces the optimum case
when the device is enabled. To enable the device the DISC1
and DISC2 Pins must be pulled logic High, Open, or any
combination of both High and Low. During this mode of
operation, quiescent current is 6mA and the device will
Acting as a near ideal line ter-
DISC1
DISC2
TERM POWER
THERMAL
LIMITING
CIRCUIT
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
9 - C
H A N N E L
DISC1
Open
P
P
H
H
L
L
R O D U C T I O N
F U N C T I O N A L D E S C R I P T I O N
OWER
P
U
L U G A N D
DISC2
Open
B L O C K D I A G R A M
P
/ P
H
H
L
L
CURRENT
BIASING
CIRCUIT
OWER
Outputs
Disabled
D
Enabled
Enabled
Enabled
Enabled
P
OWN
L A Y
D
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 logic Low.
This mode of operation places the device in a sleep state where
LX5218 has been optimized to have only 3pF of capacitance
per output in the sleep state.
active negation drivers. The device handles up to 60mA of
sink current for drivers which exceed the 2.85V output high.
A T A
An additional feature of the LX5218 is its compatibility with
F
S C S I T
UNCTION
S
Quiescent
Current
H E E T
275µA
LIMITING CIRCUIT
24mA CURRENT
E R M I N A T O R
6mA
6mA
6mA
6mA
T
ABLE
2.85V
a meager 275µA of quiescent cur-
rent is consumed. Additionally, all
outputs are in a Hi-Z (impedance)
state. Sleep mode can be used for
power conservation or to com-
pletely eliminate the terminator
from the SCSI chain. In the second
case, termination node capacitance
is important to consider. The ter-
minator will appear as a parasitic
distributed capacitance on the line,
which can detract from bus per-
formance.
1 OF 9 CHANNELS
For this reason, the
DATA OUTPUT
PIN DB(0)
UltraMAX
Copyright © 1997
Rev. 1.7
12/97