LX5122CDB MICROSEMI [Microsemi Corporation], LX5122CDB Datasheet - Page 3

• Manufacturer Part Number: LX5122CDB
• Description: ULTRA 27-LINE, PLUG AND PLAY SCSI TERMINATOR
• Manufacturer: MICROSEMI [Microsemi Corporation]

UltraMAX
Copyright © 1999
Rev. 1.0
Cable transmission theory suggests that in order to optimize
signal speed and quality, the termination should act both as
an ideal voltage reference when the line is released (de-asserted)
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
6/99
DISC1
DISC1
H
H
L
L
L
L
L
L
L
L
L
V
CC
V
DISC2
CC
DISC2
P
H
H
L
L
L
L
L
L
L
L
L
OWER
1.4V
U
P
W1
DC
DC
DC
H
H
H
H
L
L
L
L
/ P
P R O D U C T D A T A B O O K 1 9 9 6 / 1 9 9 7
ULTRA 27-L
OWER
TERM POWER
W2
DC
DC
DC
H
H
H
H
L
L
L
L
D
P
OWN
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
N1
DC
DC
DC
H
H
H
H
L
L
L
L
F
UNCTION
INE
B L O C K D I A G R A M
, P
Disabled
Disabled
Disabled
Disabled
Disabled
Disabled
Enabled
Enabled
Enabled
Enabled
Enabled
T1-T18
LUG AND
T
ABLE
CURRENT
BIASING
D
CIRCUIT
P
linearly by the equation V = I * R. The UltraMAX LX5122, with
its unique new architecture, applies the maximum amount of
current regardless of line voltage until the termination high
threshold (2.85V) is reached.
reproduces the optimum case when the device is enabled. To
enable the device the DISC1 and DISC2 pins must be driven
Disabled
Disabled
Disabled
Disabled
T19-T27
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
Enabled
A T A
LAY
Acting as a near ideal line terminator, the LX5122 closely
SCSI T
S
H E E T
per the above table. During this mode of operation,
quiescent current is 12mA and the device will
respond to line demands by delivering 24mA on
assertion and by imposing 2.85V on de-assertion.
Disable mode places the device in a sleep state,
where a meager 150µA of quiescent current is
consumed. Additionally, all outputs are in a Hi-
Z (impedance) state. Sleep mode can be used
for power conservation or to completely eliminate
the terminator from the SCSI chain.
patibility with active negation drivers.
ERMINATOR
An additional feature of the LX5122 is its com-
LIMITING CIRCUIT
24mA CURRENT
2.85V
1 OF 27 CHANNELS
DATA OUTPUT
PIN DB(0)
LX5122
3