AND8094 Datasheet, PDF (1/2 Pages) ON Semiconductor – Three New Tiny Switches Facilitate Video Switching

AND8094/D
Three New Tiny Switches
Facilitate Video Switching
Prepared by: Fred Zlotnick
ON Semiconductor
http://onsemi.com
APPLICATION NOTE
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.
B₁ 1
6 Select Select 1
1
GND 2
5 V_CC
0
V₊ 2
B₀ 3
4A
GND 3
6 NO
5 COM
4 NC
NLASB3157
NLAS4599 or NLAST4599
NLASB3157
NLAST4599
NLAS4599
NLAS1053
Input
Out
Figure 1.
I/O Jack
© Semiconductor Components Industries, LLC, 2003
1
April, 2003 - Rev. 1
RG-59 Cable
Figure 2.
Publication Order Number:
AND8094/D