Datasheet

75 W
S-VideoY'1Out
CVBS1Out
CVBS
R
SOC/DAC/Encoder
S-Video Y’
R
S-Video C’
R
Y'/G'
R
1
2
3
4
5
6
7
8
9
10
20
19
18
17
16
15
14
13
12
11
SD1OUT
SD2OUT
SD3OUT
DisableSD
GND
DisableHD
HD1OUT
HD2OUT
HD3OUT
BypassHD
SD1IN
SD2IN
SD3IN
NC
V
S+
NC
HD1IN
HD2IN
HD3IN
BypassSD
THS7365
Bypass
SDLPF
Bypass
HDLPF
P' /B'
B
R
P' /R'
R
R
75 W
75 W
S-VideoC'1Out
75 W
75 W
75 W
Y'/G'1Out
75 W
P’ /B'1Out
B
75 W
75 W
P' /R'1Out
R
75 W
75 W
75 W
75 W
S-VideoY'1Out
CVBS1Out
75 W
75 W
S-VideoC'1Out
75 W
75 W
75 W
Y'/G'1Out
75 W
P' /B'1Out
B
75 W
75 W
P’ /R'1Out
R
75 W
75 W
75 W
+2.7Vto
+5V
DisableHD
DisableSD
THS7365
SBOS467 – MARCH 2009 .................................................................................................................................................................................................. www.ti.com
Figure 120. Typical Six-Channel System with DC-Coupled Line Driving and Two Outputs Per Channel
One concern of dc-coupling, however, arises if the but power and thermal analysis should always be
line is terminated to ground. If the ac-bias input examined in any system to ensure that no issues
configuration is used, the output of the THS7365 has arise. Be sure to utilize RMS power and not
a dc bias on the output, such as 1.6 V. With two lines instantaneous power when evaluating the thermal
terminated to ground, this configuration allows a dc performance.
current path to flow, such as 1.6 V/75- Ω = 21.3 mA.
Note that the THS7365 can drive the line with
The result of this configuration is a slightly decreased
dc-coupling regardless of the input mode of
high output voltage swing and an increase in power
operation. The only requirement is to make sure the
dissipation of the THS7365. While the THS7365 was
video line has proper termination in series with the
designed to operate with a junction temperature of up
output (typically 75 Ω ). This requirement helps isolate
to +125 ° C, care must be taken to ensure that the
capacitive loading effects from the THS7365 output.
junction temperature does not exceed this level or
Failure to isolate capacitive loads may result in
else long-term reliability could suffer. Using a 5-V
instabilities with the output buffer, potentially causing
supply, this configuration can result in an additional
ringing or oscillations to appear. The stray
dc power dissipation of (5 V – 1.6 V) × 21.3 mA =
capacitance appearing directly at the THS7365 output
72.5 mW per channel. With a 3.3-V supply, this
pins should be kept below 220 pF for the 9.5-MHz
dissipation reduces to 36.2 mW per channel. The
filter channels and below 15 pF for the 36-MHz filter
overall low quiescent current of the THS7365 design
channels. One way to help ensure this condition is
minimizes potential thermal issues even when using
satisfied is to make sure the 75- Ω source resistor is
the TSSOP package at high ambient temperatures,
placed next to each THS7365 output pin. If a large
ac-coupling capacitor is used, the capacitor should be
placed after this resistor.
38 Submit Documentation Feedback Copyright © 2009, Texas Instruments Incorporated
Product Folder Link(s): THS7365