Datasheet

75 W
Y'/G'Out
CVBS/Sync
CVBS
+3.3V
R
DAC/Encoder
SDTV
CVBS
S-Video
Y'P’ P'
R'G'B’
B R
Y'/G'
R
P' /B'
B
R
P' /R'
R
R
1
2
3
4
5
6
7
14
13
12
11
10
9
8
CH1OUT
CH2OUT
CH3OUT
CH4OUT
V
S+
BYPASS
NC
CH1IN
CH2IN
CH3IN
CH4IN
GND
DISABLE
NC
THS7374
ToGPIOController
orGND
75 W
75 W
P' /B'Out
B
75 W
75 W
P' /R'Out
R
75 W
75 W
75 W
+3Vto+5V
THS7374
SLOS590B –JULY 2008–REVISED JANUARY 2011 www.ti.com
OUTPUT MODE OF OPERATION: DC care must be taken to ensure that the junction
COUPLED temperature does not exceed this level; otherwise,
long-term reliability could suffer. Although this
The THS7374 incorporates a rail-to-rail output stage
configuration only adds less than 10 mW of power
that can be used to drive the line directly without the
dissipation per channel, the overall low-power
need for large ac coupling capacitors, as shown in
dissipation of the THS7374 design minimizes
Figure 61. This approach offers the best line tilt and
potential thermal issues even when using the TSSOP
field tilt (or droop) performance because no ac
package at high ambient temperatures.
coupling occurs. Keep in mind that if the input is
ac-coupled, then the resulting tilt because of the input Note that the THS7374 can drive the line with dc
ac coupling is seen on the output regardless of the coupling regardless of the input mode of operation.
output coupling. The 80-mA output current drive The only requirement is to make sure the video line
capability of the THS7374 was designed to drive two has proper termination in series with the
video lines simultaneously (essentially, a 75-Ω load) output—typically 75-Ω. This termination helps isolate
while maintaining as wide an output dynamic range capacitive loading effects from the THS7374 output.
as possible. Failure to isolate capacitive loads may result in
instabilities with the output buffer, potentially causing
One concern of dc coupling, however, arises if the
ringing or oscillations to appear. The stray
line is terminated to ground. If the ac-bias input
capacitance appearing directly at the THS7374 output
configuration is used, the output of the THS7374 has
pins should be kept below 20-pF. The best way to
a dc bias on the output. With two lines terminated to
ensure this limit is maintained is to place the 75-Ω
ground, this configuration creates a dc current path
series output resistor as close as possible to the
that results in a slightly decreased high output voltage
output pin. If an output capacitor is used, as
swing and an increase in power dissipation of the
discussed in the next section, then it should be
THS7374. While the THS7374 was designed to
placed after the resistor.
operate with a junction temperature of up to +125°C,
Figure 61. Typical SDTV System with DC-Coupled Line Driving
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Product Folder Link(s): THS7374