THS7375IPWR datasheet(22/36 Pages) TI

22 / 36 page

OUTPUT MODE OF OPERATION:

75 W

Y'/G'Out

CVBS/Sync

CVBS

+1.8V

DaVinci

DMxxxx

Y'/G'

P' /B'

P' /R'

CH1OUT

CH2OUT

CH3OUT

CH4OUT

S+

BYPASS

CH1IN

CH2IN

CH3IN

CH4IN

GND

DISABLE

THS7375

ToGPIOController

orGND

75 W

P' /B'Out

75 W

P' /R'Out

75 W

+3Vto+5V

THS7375

SBOS449 – SEPTEMBER 2008......................................................................................................................................................................................... www.ti.com

This mode of operation is recommended for use with

that results in a slightly decreased high output voltage

chroma (C’), P’B, P’R, U’, V’, and non-sync R'G'B’

swing and an increase in power dissipation of the

signals. This method can also be used with signals

THS7375. While the THS7375 was designed to

with sync, if desired. The benefit of using the STC

operate with a junction temperature of up to +125°C,

function is that it maintains a constant back-porch

care must be taken to ensure that the junction

voltage as opposed to a back-porch voltage that

temperature does not exceed this level; otherwise,

fluctuates depending on the video content. Because

long-term

reliability

could

suffer.

Although

this

the corner frequency of the input is a very low 2.5 Hz,

configuration only adds less than 10 mW of power

the corner frequency of the input is also a very low

dissipation

per

channel,

the

overall

low-power

2.5 Hz, which is respectable performance relative to a

dissipation

the

THS7375

design

minimizes

STC configuration.

potential thermal issues even when using the TSSOP

package at high ambient temperatures.

Note that the THS7375 can drive the line with dc

DC-COUPLED

coupling regardless of the input mode of operation.

The only requirement is to make sure the video line

The THS7375 incorporates a rail-to-rail output stage

has

proper

termination

series

with

the

that can be used to drive the line directly without the

output—typically 75-

Ω. This termination helps isolate

need for large ac coupling capacitors, as shown in

capacitive loading effects from the THS7375 output.

Figure 50. This approach offers the best line tilt and

Failure to isolate capacitive loads may result in

field tilt (or droop) performance because no ac

instabilities with the output buffer, potentially causing

coupling occurs. Keep in mind that if the input is

ringing

oscillations

appear.

The

stray

ac-coupled, then the resulting tilt because of the input

capacitance appearing directly at the THS7375 output

ac coupling is seen on the output regardless of the

pins should be kept below 22-pF. The best way to

output coupling. The 80-mA output current drive

ensure this limit is maintained is to place the 75-

Ω

capability of the THS7375 was designed to drive two

series output resistor as close as possible to the

video lines simultaneously (essentially, a 75-

Ω load)

output pin. If an output capacitor is used, as

while maintaining as wide an output dynamic range

discussed in the next section, then it should be

as possible.

placed after the resistor.

One concern of dc coupling, however, arises if the

line is terminated to ground. If the ac-bias input

configuration is used, the output of the THS7375 has

a dc bias on the output. With two lines terminated to

ground, this configuration creates a dc current path

Figure 50. Typical SDTV System with DC-Coupled Line Driving

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THS7375IPWR Datasheet(PDF) 22 Page - Texas Instruments

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