4

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Application Information

IMP5111/IMP5112 Maximizes Line Current

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 IMP5111/5112, with their unique architecture, applies the

maximum amount of current regardless of line voltage until the

termination high threshold (2.85V) is reached.

Disable /Sleep Mode

The IMP5111 has an active LOW disconnect pin, and the IMP5112

has an active HIGH disconnect pin. The disable mode is entered

if the disconnect pin on either device is left open.

When disabled the termination lines are in a high impedance

state, and the power supply current drops to 275

µA typically. The

disable mode can be used to save power or completely eliminate

the terminator from the SCSI bus.

Disabled terminators appear as distributed capacitance on the

bus. The IMP5111/5112 have been optimized to have only 3pF of

capacitance per output when in the disabled mode.

The IMP5111/5112 are compatible with active negation drivers.

The devices will handle up to 60mA of sink current for drivers

which exceed the 2.85V output high level

.

VV

R

I

REF

LINE

−

()

= .

Figure 3.

5111/5112_03.eps

1 Meter, AWG 28

IMP5111

IMP5112

Receiver

Driver

IMP5111

IMP5112

Figure 1. Receiving Waveform – 20MHz

Figure 2. Driving Waveform – 20MHz

1

1

1

5

P

M

I

T

C

E

N

N

O

C

S

I

D

2

1

1

5

P

M

I

T

C

E

N

N

O

C

S

I

D

s

t

u

p

t

u

Ot

n

e

r

r

u

C

t

n

e

c

s

e

i

u

Q

HL

d

e

l

b

a

n

EA

m

6

LH

e

c

n

a

d

e

p

m

I

h

g

i

H

/

d

e

l

b

a

s

i

D5

7

2

µA

n

e

p

On

e

p

Oe

c

n

a

d

e

p

m

I

h

g

i

H

/

d

e

l

b

a

s

i

D5

7

2

µA

s

p

e

.

a

4

0

t

_

2

1

1

5

/

1

1

1

5

Table 1. Power Up/ Power Down Function Table

IMP5

IMP5