LT1739 Ver la hoja de datos (PDF) - Linear Technology

Número de pieza

componentes Descripción

Fabricante

LT1739

Dual 500mA, 200MHz xDSL Line Driver Amplifier

Linear Technology 

LT1739

APPLICATIO S I FOR ATIO

Using DC blocking capacitors, as shown in Figure 16, to

AC couple the signal to the transformer eliminates the

possibility for DC current to flow under any conditions.

These capacitors should be sized large enough to not

impair the frequency response characteristics required for

the data transmission.

Another important fault related concern has to do with

very fast high voltage transients appearing on the tele-

phone line (lightning strikes for example). TransZorbs®,

varistors and other transient protection devices are often

used to absorb the transient energy, but in doing so also

create fast voltage transitions themselves that can be

coupled through the transformer to the outputs of the line

driver. Several hundred volt transient signals can appear

at the primary windings of the transformer with current

into the driver outputs limited only by the back termination

resistors. While the LT1739 has clamps to the supply rails

at the output pins, they may not be large enough to handle

the significant transient energy. External clamping diodes,

such as BAV99s, at each end of the transformer primary

help to shunt this destructive transient energy away from

the amplifier outputs.

TransZorb is a registered trademark of General Instruments, GSI

+IN

1000pF

110Ω

110Ω

12V

+

1/2

LT1739

–

1k

1k

24.9k

SHDN

12V –12V

0.1µF

12.7Ω

BAV99

1:2

LINE

LOAD

–

0.1µF

1/2

12.7Ω

LT1739

–IN

+

SHDNREF

BAV99

–12V

12V –12V

1739 F16

Figure 16. Protecting the Driver Against Load Faults and Line Transients

1739fas, sn1739

15

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