ST AN2526 APPLICATION NOTE

AN2526

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Application note

STMAV340 evaluation board & PCB layout recommendation

Introduction

STMA V34 0 has 4 chan nels an d a 2 to 1 video switch that is well suited for switching analog
video signals on a TV or monitor set. Below is a diagram of STMAV340 typical application
configuration. As illustrated on the picture below , the 3 channels of the s witch can be used to
switch two complete sets of RGB a nd YPbPr to a single RGB/YPbPr output. One additio nal
channel can be used to switch 2 CBVS inputs to a single output that can be directly
connected to a single CVBS receiver input.

Without STMAV340 integrated in the system, the video receiver needs to have more input
pins to accommodate the many video inputs at the back panel. With the introduction of
STMAV340, less IO pins are required at the video receiver. Together with the optimized pin
arrangement, the result is a straightforward system design and overall cost reducti on.

STMAV340 in a TV application

VIDEO RECEIVER

G/Pb B/P

CVBS

STMAV340

R Y G Pb B Pr CVBS1/2

H/V SYNC

ID/VESA

April 2007 Rev 1 1/10

www.st.com

Contents AN2526

Contents

1 Evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 3

2 PCB layout recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 6

3 Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 9

2/10

AN2526 Evaluation board

1 Evaluation board

The evaluation board was designed with trouble-free customer evaluation in mind. Instead
of having two sets of RGB (VGA connector) and YPbPr (RCA connector) as inputs and
branching the output to the VGA and RCA connectors, two VGA RGB inputs are connected
and the outputs go directly to single VGA connector t o a display unit.

For the evaluation, the customer can connect the two sets of inputs to two VGA port of PC,
while the output can be directly connected to the VGA port of the display unit.

● Power supply

The board can be powered e ither directly f rom a DC po wer su pply or from a DC adaptor. If it
is powered from DC power supply, 5VDC is connected to the power socket labeled V
and the ground is connected to the power socket labeled GND. The board can also be
powered from a DC adaptor having output voltage of 7 V to 15 V. The DC adaptor voltage is
regulated to 5 V by the on board regulator. The DC adaptor can be center positive or
negative and it should be connected to the DC JACK.

To prevent the digital lines s witching from coup ling to the analog lines , the pow er distribution
is separated from digital and analog sections. Although STMAV340 has also two digital
lines, which are OE and SEL, it should still be powered from the analog supply because its
main function is to switch analog signals and those two digital lines are mostly static during
operation. Hence the analog lines are not disturbed b y t he digital pa rt and, as such, there is
no need to have a separate analog and digital supply for STMAV340.

CC

5V

The analog and digital sections on the board are isolated by ferrite beads.

Table 1. STMAV340 Demo board power supply

Designator Notes

V

5V Connect to 5 V of external power supply.

CC

GND Connect to ground of external power supply.

DC JACK

Connect to DC adaptor output if the board is to be powered from DC

Note: External power can be applied to either V

● Video input & output ports

There are four video input ports: VGA1, V GA2, CVBS1, and CVBS2. STMAV340 performs
the switching of these video inputs. Depending on the SEL control line, either VGA1 or
VGA2 input is directed to VGA_OUT and either CVBS1 or CVBS2 is directed to
CVBS_OUT.

Since STMAV340 does not perform the switching of VGA syn ch ro niz at ion sign als, two
STG719 are incorporated to switch both horizontal and vertical synchronization.

VGA port also has some ID signals. To pre vent clashing between ID signals from VGA input
1 and 2, the ID lines are isolated by jumpers. If VGA1 is active and to be directed to
VGA_OUT, JP1 to JP4 should be closed whereas JP5 to JP8 should be ope ned. If VGA2 is
active and to be directed to VGA_OUT, JP5 to JP8 should be closed whereas JP1 to JP4
should be opened.

adaptor. Input voltage: 7 to 15 V

5V/GND or DC JACK, but not to both.

CC

3/10