ISL59830

FN7489 Rev.1.00

Page 13 of 15

May 4, 2006

NTSC

The ISL59830, generating a negative rail internally, is ideally

suited for NTSC video with its accompanying negative-going

sync signals; easily handled by the ISL59830 without the need

of an additional supply as the ISL59830 generates a negative

rail with an internal charge pump referenced at negative 1/2

the positive supply.

YPbPr

YPbPr signals originating from a DVD player requiring three

channels of very tightly-controlled amplifier gain accuracy

present no difficulty for the ISL59830. Specifically, this

standard encodes sync on the Y channel and it is a negative-

going signal; easily handled by the ISL59830 without the need

of an additional supply as the ISL59830 generates a negative

rail placed at negative 1/2 the positive supply. Additionally, the

Pb and Pr are bipolar analog signals and the video signals are

negative-going; and again easily handled by the ISL59830.

Driving Capacitive Loads and Cables

The ISL59830, internally-compensated to drive 75

 cables,

will drive 10pF loads in parallel with 1k

 with less than 5dB of

peaking. If less peaking is required, a small series resistor,

usually between 5

 to 50, can be placed in series with the

output. This will reduce peaking at the expense of a slight

closed loop gain reduction. When used as a cable driver,

double termination is always recommended for reflection-free

performance. For those applications, a back-termination series

resistor at the amplifier's output will isolate the amplifier from

the cable and allow extensive capacitive drive. However, other

applications may have high capacitive loads without a back-

termination resistor. Again, a small series resistor at the output

can help to reduce peaking. The ISL59830 is a triple amplifier

designed to drive three channels; simply deal with each

channel separately as described in this section.

DC-Restore

When the ISL59830 is AC-coupled it becomes necessary to

restore the DC reference for the signal. This is accomplished

with a DC-restore system applied between the capacitive "AC"

coupling and the input of the device. Refer to Application

Circuit for reference DC-restore solution.

Amplifier Disable

The ISL59830 can be disabled and its output placed in a high

impedance state. The turn-off time is around 25ns and the turn-

on time is around 200ns. When disabled, the amplifier's supply

current is reduced to 80mA typically, reducing power

consumption. The amplifier's power-down can be controlled by

standard TTL or CMOS signal levels at the EN pin. The applied

logic signal is relative to GND pin. Letting the EN pin float or

applying a signal that is less than 0.8V above GND will enable

the amplifier. The amplifier will be disabled when the signal at

active.

Output Drive Capability

The ISL59830 does not have internal short-circuit protection

circuitry. A short-circuit current of 80mA sourcing and 150mA

sinking for the output is connected to half way between the

rails with a 10

 resistor. If the output is shorted indefinitely, the

power dissipation could easily increase such that the part will

be destroyed. Maximum reliability is maintained if the output

current never exceeds ±40mA, after which the electro-

migration limit of the process will be exceeded and the part will

be damaged. This limit is set by the design of the internal metal

interconnections.

Power Dissipation

With the high output drive capability of the ISL59830, it is

possible to exceed the 150°C absolute maximum junction

temperature under certain load current conditions. Therefore, it

is important to calculate the maximum junction temperature for

an application to determine if load conditions or package types

need to be modified to assure operation of the amplifier in a

safe operating area.

The maximum power dissipation allowed in a package is

determined according to:

Where:

The maximum power dissipation actually produced by an IC is

the total quiescent supply current times the total power supply

voltage, plus the power in the IC due to the load, or:

for sourcing:

for sinking:

Where:

i = Number of output channels

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