ST AN2471 APPLICATION NOTE

AN2471

Application note

STMAV335 evaluation board &

PCB layout recommendation

Introduction

STMAV335 has three sets of 3 to 1 switches that are well suited for switching analog video signals on the back panel of television sets or monitors. Below is a diagram of an STMAV335 typical application configuration:

Typical display unit back panel video input

VID EO RECEIVER

YPbPr OR RG B OR CVBS& S-VID EO

STM A V 335

Y PbPr		RG B	CV BS& S-V ID EO

As illustrated above, STMAV335 is used to switch one of the three video input sets to the video receiver. Depending on the SEL inputs, YPbPr, RGB, or CVBS&S-VIDEO signals will be directed to the video receiver. Hence less IO is required at the video receiver to handle the many different video signal inputs on the display unit back panel.

Ultimately, integrating STMAV335 to the system will result in a straightforward system design and overall cost reduction.

March 2007

Rev 1

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www.st.com

Contents	AN2471

Contents

1	Evaluation board . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		. 3
	1.1	Power supply . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	3
2	Video input & output ports . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		4
	2.1	Video input conditioning . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .	4
3	PCB layout recommendation . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		7
4	Revision history . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . .		11

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AN2471	Evaluation board

1 Evaluation board

The STMAV335 evaluation board provides the customer with straightforward evaluation on the performance and the typical use of the switch in the real system.

The boards include an STMAV335 switch, video input and output connectors, jumper for setting the control lines status, and a power supply portion.

1.1Power supply

The board can be powered either directly from a DC power supply or from a DC adaptor. If it is powered from a 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 will be 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 digital noise from coupling to the analog lines, the power distribution is separated from digital and analog sections. Though STMAV335 has also two digital lines, which are SEL1 and SEL2, it should still be powered from the analog supply. The reason is because its main function is to switch analog signals and those two digital lines are mostly static during operation. Hence the analog lines will not be disturbed by the digital part and as such, there is no need to have a separate analog and digital supply for STMAV335.

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

	Table 1.	Power connector
		Designator	Notes
	VCC5V		Connect to 5 V of external power supply.
	GND		Connect to ground of external power supply.
			Connect to DC adaptor output if the board is to be
	DC JACK		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.

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Video input & output ports	AN2471

2 Video input & output ports

STMAV335 can switch three sets of video input to a single set of video output. On the evaluation board, the three sets of video input are:

1.RGB (VGA port)

2.YPbPr (3 RCA connector)

3.CVBS (RCA connector) & S-VIDEO ( S-connector)

In the real system, the outputs of STMAV335 are directly connected to the video receiver. However for the STMAV335 evaluation board, each output line branches to three signal lines. The reason for this is because each set of different video signal has a different type of connector. During evaluation, each output line should be branched and be connected to a different video connector on the display unit back panel by a cable.

To avoid any PCB trace stub, the 1 to 3 branching of each output line cannot be shorted on the board. The branching of the output line is done by a zero ohm resistor. Depending on which particular set of video signal is active, the zero ohm resistors should be soldered such that the output of STMAV335 is connected to the right video output connector.

	Table 2.	Evaluation board video input & output
	Input		Output	SEL	0Ω Jumper output
				SEL1 = ‘1’	J11	= ‘R’
	RGB (VGA_IN)		RGB (VGA_OUT)		J12	= ‘G’
				SEL2 = ‘0’
					J13	= ‘B’
	Y (Y_IN)		Y (Y_OUT)	SEL1 = ‘0’	J11	= ‘Y’
	Pb (Pb_IN)		Pb (Pb_OUT)		J12	= ‘Pb’
				SEL2 = ‘1’
	Pr (Pr_IN)		Pr (Pr_OUT)		J13	= ‘Pr’
	CVBS (CVBS_IN)		CVBS (CVBS_OUT)	SEL1 = ‘0’	J11	= ‘CVBS’
	S-VIDEO		S-VIDEO		J12	= ‘Y(S)’
				SEL2 = ‘0’
	(S VIDEO_IN)		(S VIDEO_OUT)		J13	= ‘C’
Note:	SEL1→ JP9, SEL2 → JP10, OPEN = '1' & CLOSE = '0'

2.1Video input conditioning

The blanking level might vary between different video transmitters. This STMAV335 evaluation board can handle video signals with blanking level of 0V to 2.5 V.

If video signal blanking levels are outside the above range, some input conditioning should be done to modify the blanking level to the range specified.

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