4

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Application Information

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 IMP5225, 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 IMP5225 closely repro-

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

the device the DISC1 and DISC2 pins are pulled HIGH. 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 DISC1 and DISC2 pins must be

driven LOW. 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 IMP5225 is its compatibility with

active negation drivers.

VV

R

I

REF

LINE

−

()

= .

1

T

C

E

N

N

O

C

S

I

D2

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

HH

d

e

l

b

a

s

i

DA

m

5

1

HL

d

e

l

b

a

n

EA

m

5

1

LH

d

e

l

b

a

n

EA

m

5

1

LL

d

e

l

b

a

s

i

DA

µ

0

5

1

n

e

p

On

e

p

Od

e

l

b

a

s

i

DA

µ

0

5

1

s

p

e

.

4

0

t

_

5

2

2

5

Figure 3.

Table 1. Power Up/ Power Down Function Table

5225_03.eps

DISCONNECT 1

1 Meter, AWG 28

DISCONNECT 2

IMP5225

DISCONNECT 1

Receiver

Driver

DISCONNECT 2

IMP5225

Figure 1. Receiving Waveform – 20MHz

Figure 2. Driving Waveform – 20MHz

IMP5

IMP5225

IMP5225