THS7353 Datasheet, PDF (21/51 Pages) Texas Instruments – 3-Channel Low Power Video Buffer with I2C Control, Selectable Filters, External Gain Control, 2:1 Input MUX, and Selectable Input Modes

THS7353
www.ti.com
SLOS484 – NOVEMBER 2005
APPLICATION INFORMATION (continued)
INPUT OVERVOLTAGE PROTECTION
The THS7353 is built using a high-speed complementary bipolar and CMOS process. The internal junction
breakdown voltages are low for these very small geometry devices. These breakdowns are reflected in the
Absolute Maximum Ratings table. All input and output device pins are protected with internal ESD protection
diodes to the power supplies, as shown in Figure 58.
V_S+
External
Input/
Output
Pin
Internal
Circuitry
Figure 58. Internal ESD Protection
These diodes provide moderate protection to input overdrive voltages above and below the supplies. The
protection diodes can typically support 30-mA of continuous current when overdriven.
TYPICAL CONFIGURATION and VIDEO TERMINOLOGY
A typical application circuit using the THS7353 as a video input buffer is shown in Figure 59. It shows the
A-channel inputs of the THS7353 buffering and filtering a set of HDTV inputs and driving a video ADC / decoder.
Although the high-definition video (HD) or enhanced-definition (ED) Y’P’_BP’_R (sometimes labeled Y’U’V’ or
incorrectly labeled Y’C’_BC’_R) channels are shown, these channels can easily be S-Video Y’/C’ channels and the
composite video baseband signal (CVBS) of a standard definition video (SD) system. These signals can also be
G'B'R' (R'G'B') signals or other variations. Note that for computer signals the sync should be embedded within
the signal for a system with only 3-signals. This is sometimes labeled as R'G'sB' (sync on green) or R'sG'sB's
(sync on all signals).
The second set of inputs (B-Channels) shown can be HD, ED, SD, or G’B’R’ video signals. The THS7353’s
flexibility allows for almost any input signal to be driven into the THS7353 regardless of the other set of inputs.
Simple control of the I²C configures the THS7353. For example, the THS7353 can be configured to have
Channel 1 Input connected to input A while Channels 2 and 3 are connected to input B. See the various sections
explaining the I²C interface later in this data sheet.
Note that the Y’ term is used for the luma channels throughout this document rather than the more common
luminance (Y) term. The reason is to account for the definition of luminance as stipulated by the CIE -
International Commission on Illumination. Video departs from true luminance since a nonlinear term, gamma, is
added to the true RGB signals to form R'G'B' signals. These R'G'B' signals are then used to mathematically
create luma (Y'). Thus luminance (Y) is not maintained requiring a difference in terminology.
This rationale is also used for the chroma (C') term. Chroma is derived from the non-linear R'G'B' terms and thus
it is nonlinear. Chominance (C) is derived from linear RGB giving the difference between chroma (C') and
chrominance (C). The color difference signals (P'_B / P'_R / U' / V') are also referenced this way to denote the
nonlinear (gamma corrected) signals.
R'G'B' (commonly mislabeled RGB) is also called G'B'R' (again commonly mislabeled as GBR) in professional
video systems. The SMPTE component standard stipulates that the luma information is placed on the first
channel, the blue color difference is placed on the second channel, and the red color difference signal is placed
on the third channel. This is consistent with the Y'P'_BP'_R nomenclature. Because the luma channel (Y') carries the
sync information and the green channel (G') also carries the sync information, it makes logical sense that G' be
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