THS7303 Datasheet, PDF (27/43 Pages) Texas Instruments – 3-Channel Low Power Video Amplifier with I2C Control, Selectable Filters, 6-dB Gain, SAG Correction, 2:1 Input MUX, and Selectable Input Bias Modes

THS7303
www.ti.com
SLOS479 – OCTOBER 2005
APPLICATION INFORMATION (continued)
THS7303. While the THS7303 is 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.
Although this configuration adds less then 10 mW of power dissipation per channel, the overall low power
dissipation of the THS7303 design minimizes potential thermal issues even when using the TSSOP package at
high ambient temperatures.
3.3 V
G’
DAC /
Encoder
(THS8200)
B’
R’
G’
B’
R’
R
R
R
0.1 mF
75 W
0.1 mF
75 W
0.1 mF
75 W
DC + 135 mV
1 NC
NC 20
DC + 135 mV
DC + 135 mV
AC STC
AC STC
AC STC
2 CH.1 IN A
3 CH.2 IN A
4 CH.3 IN A
5 CH.1 IN B
6 CH.2 IN B
7 CH.3 IN B
CH.1 OUT 19
CH. 1 SAG 18
CH.2 OUT 17
CH. 2 SAG 16
CH.3 OUT 15
CH. 3 SAG ¹⁴
8 I 2C-A1
SCL 13
9 I 2C-A0
10 GND
SDA 12
V_S+ 11
0.01 mF
G’
75 W ^Out
B’
75 W ^Out
R’
75 W ^Out
+Vs
+
100 mF
2
IC
Controller
75 W
75 W
75 W
External
Input
Figure 64. Typical G'B'R' (R'G'B') System With DC-Coupled Line Driving
Note that the THS7303 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 pin – typically 75-Ω.
This helps isolate capacitive loading effects from the THS7303 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 THS7303 output pins should be kept below 25-pF for best performance.
When driving 2 video lines, each line should have its own 75-Ω source termination resistors to isolate the lines
from each other.
OUTPUT MODES OF OPERATION – AC COUPLED
The most common method of coupling the video signal to the line is by using a large capacitor. This capacitor is
typically between 220 µF and 1000 µF, although 470 µF is most common. This value of this capacitor must be
this large to minimize the line tilt (droop) and/or field tilt associated with ac coupling as described previously in
this document. Just like the dc output configuration, connection of the output pin of each channel directly to the
SAG output pin of the corresponding channel should be as close as possible to the output pins of the THS7303.
The most common reason ac coupling is used is to ensure full interoperability with the receiving video system.
This eliminates possible ground loops. It also ensures that regardless of the reference dc voltage used on the
transmit side, the receive side can re-establishes the dc reference voltage to its own requirements.
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