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Application Information

IMP5219 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 IMP5219, with its unique new architecture, applies the maxi-

mum amount of current regardless of line voltage until the

termination high threshold (2.85V) is reached.

Acting as a near ideal line terminator, the IMP5219 closely repro-

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

device the Disable pin must be driven HIGH or left Open. When

enabled, quiescent current is 6mA and the device will respond to

line demands by delivering 24mA on assertion and by imposing

2.85V on de-assertion.

Disable/Sleep Mode

Disable mode places the device in a sleep state, where quiescent

current typically 375

µA. When disabled, all outputs are in a high

impedance state and output capacitance is a low 3pF. Sleep mode

can be used for power conservation or to remove the terminator

from the SCSI chain.

An additional feature of the IMP5219 is its compatibility with

active negation drivers.

Table 1. Power Up/ Power Down Function Table

e

l

b

a

s

i

Ds

t

u

p

t

u

Ot

n

e

r

r

u

C

t

n

e

c

s

e

i

u

Q

Hd

e

l

b

a

n

EA

m

6

L

h

g

i

H

/

e

l

b

a

s

i

D

e

c

n

a

d

e

p

m

I

5

7

3

µA

n

e

p

Od

e

l

b

a

n

EA

m

6

s

p

e

.

4

0

t

_

9

1

2

5

VV

R

I

REF

LINE

−

()

= .

Figure 3.

5219_03.eps

1 Meter, AWG 28

IMP5219

Receiver

Driver

IMP5219

Figure 1. Receiving Waveform – 20MHz

Figure 2. Driving Waveform – 20MHz

IMP5

IMP52