LX5121

PRODUCT DA T ABOOK 1996/1997

3

Copyright © 1999

Rev. 1.0

5/99

UltraMAX

BLOCK DIAGRAM

FUNCTIONAL DESCRIPTION

TERM POWER

CURRENT

BIASING

CIRCUIT

1.4V

DISC2

24mA CURRENT

LIMITING CIRCUIT

DATA OUTPUT

PIN DB(0)

2.85V

1 OF 27 CHANNELS

DISC1

V

CC

V

CC

Cable transmission

theory suggests that in

order to optimize sig-

nal speed and quality,

the

termination

should act both as an

ideal voltage refer-

ence when the line is

released (de-asserted)

and as an ideal current

source when the line

is active (asserted).

Common active termi-

nators, which consist

of Linear Regulators in

series with resistors

(typically 110

Ω), are a

compromise.

As the

line voltage increases, the amount of current decreases linearly

by the equation V = I * R. The UltraMAX LX5121, with its

unique new architecture, applies the maximum amount of

current regardless of line voltage until the termination high

threshold (2.85V) is reached.

Acting as a near ideal line terminator, the LX5121 closely

reproduces the opti-

mum case when the

device is enabled. To

enable the device the

DISC1 and DISC2 pins

must be driven per the

above table.

During

this mode of operation,

quiescent current is

12mA and the device

will respond to line de-

mands 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 qui-

escent 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.

An additional feature of the LX5121 is its compatibility with

active negation drivers.

DISC1

DISC2

W1

W2

N1

T1-T18

T19-T27

H

L

DC

DC

DC

Enabled

Disabled

L

H

DC

DC

DC

Disabled

Enabled

L

L

DC

DC

DC

Disabled

Disabled

H

H

H

H

H

Enabled

Enabled

H

H

H

H

L

Enabled

Enabled

H

H

H

L

H

Enabled

Enabled

HH

H

L

L

Disabled

Enabled

H

H

L

H

H

Enabled

Enabled

HH

L

H

L

Disabled

Enabled

HH

L

L

H

Disabled

Disabled

H

H

LLL

Disabled

Disabled