© Semiconductor Components Industries, LLC, 2003

April, 2003 - Rev. 1

1

Publication Order Number:

AND8094/D

AND8094/D

Three New Tiny Switches

Facilitate Video Switching

Prepared by: Fred Zlotnick

ON Semiconductor

ON Semiconductor has just introduced four switches to

facilitate many switching functions including composite

video switching. One of the issues with today’s consumer

products is they are getting so small, there is no room for

traditional switches or extra sets of jacks needed for various

functions. One solution is to permit one set of jacks to

perform two functions, an input and an output. In this

example, we show a Digital Video Camera with analog

input/output requirements. Many consumers require the

ability to transfer their old analog tapes to digital format,

but this requires analog inputs on the camera. The size of

today’s camera is so small that providing both input jacks

and output jacks, requires too much space. One solution is

to have an A/V jack which functions as either input or

output. The onboard MCU can instruct the switch to be

either an input or output.

Any one of the four switches may be used for this

application, and they are the NLAS4599, the NLAST4599,

the NLASB3157, and the NLAS1053. The first two devices

are essentially the same, however the “T” version permits

interface to “TTL” level signals, without any additional

components. The third device is the same function as the

first two, with a slightly different pin arrangement to meet

certain customer requirements. The first two devices are

available in SOT-23 size 6-pin packages, while all three

are available in the tiny SC70 footprint, only 2

× 2 mm.

The circuitry couldn’t be simpler. These switches are all

Single Pole Double Throw (SPDT). Essentially the

common side of the part is connected to the jack center pin,

while the signal pins are connected to either the input or the

output of the camera. The resistance of the switch is low

enough not to cause much insertion loss or distortion to the

waveform. Although this application shows switching a

composite video signal, the same switch can switch the

higher bandwidth component video signals or digital signals

beyond 50 MHz as well. It is assumed that the internal

video amplifiers have their own 75

Ω matching resistors

appropriately placed. The output Video amplifier needs to

have a series 75

Ω resistor and its dc level is ≅ 2.5 V. The

input is assumed to be 75

Ω with a dc path to ground. Since

these switches are single supply, the signals passing

through them need to be between 0 and 5 Volts with white

level near mid-voltage. The dc blocking capacitor keeps

undesired dc off the input or output.

Figure 2 shows the use of these parts as described. Select

pin is connected to an MCU, the inputs and output are

connected to pins 4, 6 (4599) or 1, 3 (3157) and the jack is

either connected to 5 (4599) or 3 (4599). Vcc is assumed to

be +5 V. If a low voltage MCU is used as a controller, the

NLAST4599 can be directly interfaced to it, as long as the

supply voltage is greater than 2.3 V.

Select

GND

A

2

3

6

4

5

1

0

1NO

Select

COM

NC

GND

3

6

4

5

1

Figure 1.

NLASB3157

NLAS4599 or NLAST4599

Figure 2.

Input

Out

I/O Jack

RG-59 Cable

NLASB3157

NLAST4599

NLAS4599

NLAS1053

APPLICATION NOTE

http://onsemi.com