ST AN2705 APPLICATION NOTE

AN2705

Application note

TSH173 triple video buffer with filter for SD video evaluation board user guidelines

Introduction

This application note describes the TSH173 evaluation board, designed to help you evaluate the TSH173 triple video buffer.

This document includes:

■A short description of the TSH173 video buffer, including the internal block diagram

■A description of the evaluation board and all of its components

■The layout of the evaluation board

About the TSH173

The TSH173 is a single supply triple video buffer featuring an internal gain of 6dB and an internal low pass filter of 8.2MHz cut-off frequency for each channel to fit with Standard Definition requirements for video line interfaces.

Figure 1. TSH173 evaluation board

Main features of the TSH173

– 4.5V to 5.5V single supply operation	– No input capacitor required
– R-G-B, Y-Pb-Pr, Y-C-CVBS driving	– Very low harmonic distortion
– 3 channels with 6dB gain buffer	– Each output can drive ACor DC-coupled 150Ωloads
– 3 video reconstruction filters for SD	– Tested on 5V power supply
– 3 internal input DC level shifter
January 2008	Rev 1	1/8

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TSH173 description	AN2705

1 TSH173 description

Figure 2. TSH173 internal block diagram

Table 1.	Pin description
	Name	Pin number	Description
IN1, IN2, IN3		1, 2, 3	Input pins
OUT1, OUT2, OUT3		8, 7, 6	Output pins
+VCC		4	Positive supply
GND		5	Ground

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AN2705	Evaluation board description

2 Evaluation board description

This board is designed to be tested with a 75Ωgenerator and 75Ωmeasurement tool.

Input signal must be between 0V and 1.4V so that it is not clamped. Otherwise, you must replace the zero ohm resistor by a 100nF capacitor in CR1, CR2, and CR3, and add a resistor bridge to polarize the input signal at the right level as shown in Figure 3. Resistor bridge footprints are located on the back of the PCB.

Figure 3. TSH173 input

The TSH173 output can be AC coupled by a 220nF capacitor to minimize the DC component on the line. To do this, you must remove the R4, R11, and R18 zero ohm resistors and solder a 220µF capacitor on C6, C8, and C10 footprints as shown in Figure 4.

Figure 4. TSH173 AC output

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