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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 x 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 matching resistors appropriately placed. The output Video amplifier needs to have a series 75 resistor and its dc level is 2.5 V. The input is assumed to be 75 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 1 GND 2 0 B0 3 NLASB3157
6 5 4
Select VCC A
Select 1 V+ 2 GND 3
6 NO 5 COM 4 NC Input
NLASB3157 NLAST4599 NLAS4599 NLAS1053 Out
NLAS4599 or NLAST4599
Figure 1.
I/O Jack
RG-59 Cable
Figure 2.
(c) Semiconductor Components Industries, LLC, 2003
1
April, 2003 - Rev. 1
Publication Order Number: AND8094/D
AND8094/D
SENSEFET is a trademark of Semiconductor Components Industries, LLC.
ON Semiconductor and are registered trademarks of Semiconductor Components Industries, LLC (SCILLC). SCILLC reserves the right to make changes without further notice to any products herein. SCILLC makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does SCILLC assume any liability arising out of the application or use of any product or circuit, and specifically disclaims any and all liability, including without limitation special, consequential or incidental damages. "Typical" parameters which may be provided in SCILLC data sheets and/or specifications can and do vary in different applications and actual performance may vary over time. All operating parameters, including "Typicals" must be validated for each customer application by customer's technical experts. SCILLC does not convey any license under its patent rights nor the rights of others. SCILLC products are not designed, intended, or authorized for use as components in systems intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the SCILLC product could create a situation where personal injury or death may occur. Should Buyer purchase or use SCILLC products for any such unintended or unauthorized application, Buyer shall indem nify and hold SCILLC and its officers, employees, subsidiaries, affiliates, and distributors harmless against all claims, costs, damages, and expenses, and reasonable attorney fees arising out of, directly or indirectly, any claim of personal injury or death associated with such unintended or unauthorized use, even if such claim alleges that SCILLC was negligent regarding the design or manufacture of the part. SCILLC is an Equal Opportunity/Affirmative Action Employer.
PUBLICATION ORDERING INFORMATION
Literature Fulfillment: Literature Distribution Center for ON Semiconductor P.O. Box 5163, Denver, Colorado 80217 USA Phone: 303-675-2175 or 800-344-3860 Toll Free USA/Canada Fax: 303-675-2176 or 800-344-3867 Toll Free USA/Canada Email: ONlit@hibbertco.com N. American Technical Support: 800-282-9855 Toll Free USA/Canada JAPAN: ON Semiconductor, Japan Customer Focus Center 2-9-1 Kamimeguro, Meguro-ku, Tokyo, Japan 153-0051 Phone: 81-3-5773-3850 ON Semiconductor Website: http://onsemi.com For additional information, please contact your local Sales Representative.
http://onsemi.com
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AND8094/D

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