© 2000 IMP, Inc.

Data Communications

5

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 110

Ω) are a compromise. With coventional linear

terminators as the line voltage increases the amount of current

decreases linearly by the equation;

The IMP5226, with its unique new architecture, applies the max-

imum amount of current regardless of line voltage until the

termination high threshold (2.85V) is reached.

Acting as a near ideal line terminator, the IMP5226 closely repro-

duces the optimum case when the device is enabled. To enable

the device the disconnect pin is pulled LOW. During this mode

of operation, quiescent current is 10mA, and the device will

respond to line demands by delivering 24mA on assertion and by

imposing 2.85V on deassertion.

In order to disable the device, the disconnect pin must be driven

HIGH In the disable mode, the device is in a sleep state with

quiescent current less than 150

µA. When disabled, all

outputs are in a high impedance state. Sleep mode can be used

for power conservation or to remove the terminator from the

SCSI chain.

An additional feature of the IMP5226 is its compatibility with

active negation drivers.

VV

R

I

REF

LINE

−

()

= .

Table 1. Power Up/ Power Down Function Table

Application Information

T

C

E

N

N

O

C

S

I

Ds

t

u

p

t

u

O

t

n

e

c

s

e

i

u

Q

m

u

m

i

x

a

M

t

n

e

r

r

u

C

Ld

e

l

b

a

n

EA

m

5

1

HZ

I

HA

µ

0

5

1

n

e

p

OZ

I

HA

µ

0

5

1

s

p

e

.

4

0

t

_

6

2

2

5

1

IMP5226

IMP5226