ticomaaj 3Q 2008 Texas Instruments Incorporated Interface Data Transmission Cascading of input serializers boosts channel density for digital inputs Introduction Programmable logic controllers PLCs play an integral role in industrial automation They ID: 24527
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16Analog Applications Journal www.ti.com/aaj3Q 2008Texas Instruments Incorporatedproximity switches, fuel sensors, light barriers, over-Traditionally, digital inputs used discrete componentsResistor-capacitor (RC) filters reduced bouncing ofmechanical switches, while a per-channel optocoupler however, requires bulky components, many isolation With a typical resistor chain providing about 2.2 kin power consumptions of 260 mW or 400 mW at 30 V.density. GND1GND2 Load SCLK STE SOMIGND VREG TEMPOptional RIN 0:7 Signal Conditioning Serializer 0 V24 V TI’s SN65HVS88x product family addresses these limita-lower power resistor.of the input. Without the LED, this pin simply connects nel input, it still provides a four-channel isolation, savinginterface? We previously calculated a worst-case dissipa-tion of 400 mW/channel totaling almost 13 W: this is toorange, limiting the per-channel dissipation to 90 mW at 30 V. This reduces power dissipation by more than 75% Texas Instruments Incorporated 17Analog Applications Journal components by using the integrated debounce filter, set toISO721 –High-speed digital isolatorwww.ti.com/iso721www.ti.com/sn65hvs882 ISO72414 x SN65HVS880Host ControllerINALoad OUTBINBSTE OUTCINCSCLK INDOUTDSOMI SOPIP7IP0CLKCELDSIP Serializer SOPIP7CLKCELDSIP Serializer SOPIP7CLKCELDSIP Serializer SOPIP7CLKCELDSIP Serializer Figure 2. Simplified 32-channel digital input with cascading,using four HVS88x serializers and one ISO7241 digital isolator PARAMETER SN65HVS880 SN65HVS882 Serialization Yes Yes Cascading Yes Yes Current Limitation Yes Yes Debounce Filter Yes Yes VCC 18 V to 30 V 10 V to 34 V Undervoltage Indicator Yes (~15 V) No 5-V Output Yes Yes Input Voltage Range 0 V to 30 V 0 V to 34 V Temperature Range –40°C to 85°C –40°C to 125°C Over-Temperature Protection Yes Yes Table 1. The SN65HVS88x digital input serializer family digital isolator IMPORTANT NOTICE Texas Instruments Incorporated and its subsidiaries (TI) reservestandard warranty. Testing and other quality control techniques areused to the extent TI deems necessary to support this warranty.applications using TI components. To minimize the risksunder the patents or other intellectual property of the third party, or aTexas Instruments products and application solutions: TIWorldwide Technical Support InternetTI Semiconductor Product Information Center Home Pagesupport.ti.comTI Semiconductor KnowledgeBase Home Pagesupport.ti.com/sc/knowledgebase Phone+1(972) 644-5580Fax+1(972) 927-6377 Internet/Emailsupport.ti.com/sc/pic/americas.htmEuropean Free Call00800-ASK-TEXASInternational+49 (0) 8161 80 2121Russian Support+7 (4) 95 98 10 701The European Free Call (Toll Free) number is not active in all countries. If you havetechnical difficulty calling the free call number, please use the international number above.Fax+(49) (0) 8161 80 2045 International+81-3-3344-5317Domestic0120-81-0036Internationalsupport.ti.com/sc/pic/japan.htm Domesticwww.tij.co.jp/picInternational+886-2-23786800DomesticToll-Free NumberToll-Free NumberAustralia1-800-999-084Malaysia1-800-80-3973China800-820-8682New Zealand0800-446-934Hong Kong800-96-5941Philippines1-800-765-7404India+91-80-41381665 (Toll)Singapore800-886-1028Indonesia001-803-8861-1006Taiwan0800-006800Korea080-551-2804Thailand001-800-886-0010Fax+886-2-2378-6808Emailtiasia@ti.comInternetsupport.ti.com/sc/pic/asia.htmti-china@ti.com of similar import. Similarly, such statements herein that describethe company's products, business strategy, outlook, objectives,of operations. We disclaim any intention or obligation to updateTrademarks: Mailing Address: Texas InstrumentsDallas, Texas 75265 Texas Instruments Incorporated Telephony Video & Imaging www.ti.com/wireless SLYT