THS7364_10 Datasheet, PDF (33/47 Pages) Texas Instruments – 6-Channel Video Amplifier with 3 SD and 3 Full-HD Filters with 6-dB Gain

THS7364
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CVBS
S-Video Y’
S-Video C’
Y'/G'
P'_B/B'
P'_R/R'
THS7364
1 SD1 IN
SD1 OUT 20
R
2 SD2 IN
SD2 OUT 19
3 SD3 IN
SD3 OUT 18
4 NC
R
+2.7 V to
+5 V
5 V_S+
6 NC
Disable SD 17
GND 16
Disable FHD 15
Disable SD
Disable FHD
7 FHD1 IN FHD1 OUT 14
R
8 FHD2 IN FHD2 OUT 13
9 FHD3 IN FHD3 OUT 12
10 Bypass SD Bypass FHD 11
R
Bypass
SD LPF
R
Bypass
FHD LPF
R
CVBS 1 Out
75 W
S-Video Y' 1 Out
75 W
S-Video C' 1 Out
75 W
Y'/G' 1 Out
75 W
P’_B/B' 1 Out
75 W
P'_R/R' 1 Out
75 W
SBOS530 – AUGUST 2010
CVBS 1 Out
75 W
75 W
75 W
S-Video Y' 1 Out
75 W
75 W
75 W S-Video C' 1 Out
75 W
75 W
75 W
Y'/G' 1 Out
75 W
75 W
75 W
P'_B/B' 1 Out
75 W
75 W
75 W
P’_R/R' 1 Out
75 W
75 W
75 W
(1) Figure 81. Typical Six-Channel System with DC-Coupled Line Driving and Two Outputs Per Channel
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 THS7364 has
a dc bias on the output, such as 1.6 V. With two lines
terminated to ground, this configuration allows a dc
current path to flow, such as 1.6 V/75-Ω = 21.3 mA.
The result of this configuration is a slightly decreased
high output voltage swing and an increase in power
dissipation of the THS7364. While the THS7364 was
designed to operate with a junction temperature of up
to +125°C, care must be taken to ensure that the
junction temperature does not exceed this level or
else long-term reliability could suffer. Using a 5-V
supply, this configuration can result in an additional
dc power dissipation of (5 V – 1.6 V) × 21.3 mA =
72.5 mW per channel. With a 3.3-V supply, this
dissipation reduces to 36.2 mW per channel. The
overall low quiescent current of the THS7364 design
minimizes potential thermal issues even when using
the TSSOP package at high ambient temperatures,
but power and thermal analysis should always be
examined in any system to ensure that no issues
arise. Be sure to use RMS power and not
instantaneous power when evaluating the thermal
performance.
Note that the THS7364 can drive the line with
dc-coupling regardless of the input mode of
operation. The only requirement is to make sure the
video line has proper termination in series with the
output (typically 75 Ω). This requirement helps isolate
capacitive loading effects from the THS7364 output.
Failure to isolate capacitive loads may result in
instabilities with the output buffer, potentially causing
ringing or oscillations to appear. The stray
capacitance appearing directly at the THS7364 output
pins should be kept below 20 pF for the fixed SD filter
channels and below 15 pF for the FHD filter
channels. One way to help ensure this condition is
satisfied is to make sure the 75-Ω source resistor is
placed within 0.5 inches, or 12.7 mm, of the THS7364
output pin. If a large ac-coupling capacitor is used,
the capacitor should be placed after this resistor.
Copyright © 2010, Texas Instruments Incorporated
Product Folder Link(s): THS7364
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