ST AN2526 APPLICATION NOTE

AN2526

Application note

STMAV340 evaluation board & PCB layout recommendation

Introduction

STMAV340 has 4 channels and 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 switch can be used to switch two complete sets of RGB and YPbPr to a single RGB/YPbPr output. One additional 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 reduction.

STMAV340 in a TV application

VIDEO RECEIVER

R/Y

G/Pb

B/Pr

CVBS

H/V SYNC

STMAV340

ID/VESA

R Y

G Pb

B Pr

CVBS1/2

April 2007

Rev 1

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Contents	AN2526

Contents

1	Evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	3
2	PCB layout recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	6
3	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	9

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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 to 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 either directly from a DC power supply or from a DC adaptor. If it is powered from DC power supply, 5VDC is connected to the power socket labeled VCC5V 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 switching from coupling to the analog lines, the power 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 by the digital part and, as such, there is no need to have a separate analog and digital supply for STMAV340.

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

	Table 1.	STMAV340 Demo board power supply
	Designator		Notes
		VCC5V	Connect to 5 V of external power supply.
		GND	Connect to ground of external power supply.
		DC JACK	Connect to DC adaptor output if the board is to be powered from DC
			adaptor. Input voltage: 7 to 15 V
Note:	External power can be applied to either VCC5V/GND or DC JACK, but not to both.

●Video input & output ports

There are four video input ports: VGA1, VGA2, 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 synchronization signals, two STG719 are incorporated to switch both horizontal and vertical synchronization.

VGA port also has some ID signals. To prevent 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 opened. If VGA2 is active and to be directed to VGA_OUT, JP5 to JP8 should be closed whereas JP1 to JP4 should be opened.

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