AN-534 ᆌᆩԴऻ One Technology Way s P.O. Box 9106 s Norwood, MA 02062-9106 s 781/329-4700 s World Wide Web Site: http://www.analog.com ֑ᆩ20C15* HARTۙۙഗྺ࣍ୟࠃۉ႙4 mA–20 mA DAC AD421ሺཁHART®Ⴀీ ፕኁ;Albert O’Grady ० AD421ᅃྜኝڦຕጴ๕࣍ୟࠃۉ4 mA–20 mAገ࣑ഗLj ጆோኍ߾ܔᄽ੦ႜᄽڦీ݀พഗሰฆڦ༬ۨႴ൱ܸ ยऺăፕྺᅃዖྜඇणߛڦׯ܈ĂׯگԨਦݛӄLj ഗॲ֑ᆩٙ႙16ᆅগހጎLjᅜटׯگԨ༵ߛీ4 mA–20 mA݀พഗݴՐ୲ڦၙኮăHART(ლᇺߌدײഗ ߛཚ)ڢཚ႑ၹᅱሞᄽহԥ࠽ݘথLjएᇀీ၄ׇᅏ ڦຕጴሺഽ႙4 mA–20 mAཚ႑ڦՔጚăၹᅱ૧ᆩBell 202ೕᅎ॰੦(FSK)ՔጚLjॽۉگೝຕጴ႑ࡽ۠ेڟ4 mA–20 mAఇె႑ࡽฉăኄྺํ၄ଇዖཚ႑ݛ๕ظሰକཉॲLj๑ ࠕీڥሞዷᄲײࡗڦՎଉኮྔሞీ၄ׇᅏઠ࣮ܮڿد ྔ႑တăSymbios LogicڦSYM20C15ኼሞྺᆩࢽํ၄ᅃ ߲ग़ඹHARTڦ֫ظሰཉॲăഗॲཚࡗՂᄲۙڦ ĂۙĂሜհॠ֪Ăհႚႚټࢅׯཚ୳հॽၹᅱሞೌ ฉํ၄ăHARTၹᅱሞփዐ4 mA–20 mA႑ࡽڦ൧ူ ႜཚ႑Lj๑ዷऐᆌᆩײႾ(ዷऐ)௱ٗ၄ׇഗॲइ ڥଇ߲ई߸߸ܠႎຕጴăᆯᇀຕጴFSK႑ࡽਏᆶ၎࿋Ⴤ ႠLjᅺُփࣷܔ4 mA–20 mA႑ࡽሰ߅ׯඡăස2๖Ljܾ ڦ1ࢅ0ݴ՚ᆩଇ߲փཞೕ୲1200 Hzࢅ2200 Hzپă ኄၵຕጴ႑ࡽᅜۉگೝࢅೝኵྺଭڦኟ၀հ۠ेሞୁ ႑ࡽฉLjᅺُLjஃ၍ୟዐ݀ޏໃຕጴ႑ࡽLjۼփࣷᆶ ୁݴଉ۠ेڟ၄ᆶ4 mA–20 mA႑ࡽฉăᅺُLj၄ᆶڦఇ ెᅏධሞ֑ᆩHARTၹᅱڦဣཥዐኟሏႜǗᅺྺگ ཚ୳հഗၩأຕጴ႑ࡽăᅃ߲ڇटۅ10 Hzگཚ୳հഗ ॽཚ႑႑ࡽᆶၳইگᅃ߲၎ړᇀଉײ႑ࡽ0.01%ፑᆸ ڦ࿖հă2๖ྺ֑ᆩHARTၹᅱڦ၄ׇᅏڦă APPROX 0.5mA MEMORY SENSORS APPROX 0.5mA A/D CONVERTER MICROPROCESSOR D/A CONVERTER 4mA TO 20mA MEASUREMENT CIRCUIT COMMUNICATION SYSTEM 1200Hz "1" 2200Hz "0" 1 ֑ᆩHARTၹᅱڦຕጴد *20C15ᆯSymbios LogicࠃऋLjဣࣆۉǖ(408) 433-8000ă HARTHARTཚ႑एূࣷڦጀ֩ฆՔă 2 ీ၄ׇᅏ ԨᆌᆩԴऻዷᄲت࣍ୟࠃۉ႙4 mA–20 mA DAC AD421 ᇑ20C15 HARTۙۙഗኮक़ڦথ੨࿚༶Ljཞ้༑༪ํ၄ ग़ඹHARTၹᅱڦᅏႴڦՂᄲօየă AN-534 AD421ୁۉ੦ۉୟ ስ᳘ࢇۉඹCC AD421ాዃᅃ߲16-࿋Σ-Δ DACLjᆩᅜॽሜ٪ഗڦ ຕጴ႑တገ࣑ྺୁۉăΣ-ΔॐࠓݴՐ୲ߛLjሞۙڇႠݛ௬ ਏᆶڥཀڦࢩ܀ᆫLjᆮഄᆩᇀټᄲ൱၎ܔড߾ڦگ ᄽ੦࣍ৣăAD421ᅜԍኤ16࿋ೝۙڇڦႠă ࣍ୟฉڦHART႑ࡽྺ1 mAރރኵLjසമຎLjኄᅜ ሞAD421ాևཚࡗၠC3ᆅগแेࢇۉڦუ႑ࡽઠׂิă HARTၹᅱཞ้ኧຕጴࢅఇెཚ႑LjᅺُLjጀ࣍ୟڦ ຕጴHART႑ࡽփ߅ڥඡఇె࣍ୟڦୁۉኵLjኄᅃۅๆ ݴዘᄲăHART႑ࡽ֑ᆩୁ᳘ࢇఇ๕LjᅜՆ௨ᆅഐٱ ဃăCCࢅC3ଇ߲ۉඹܔઠጲ20C15ڦHARTۉუ႑ࡽႜ ປ३تLjᅜඓԍሞHARTدࡗײዐᆶᅃ߲1 mAރރኵڦ HART႑ࡽీ࣍ୟăC3ᆅগฉڦ႑ࡽፕᆩᇀᅃ߲40 kΩ ۉፆฉLjଇԠᇀ႑ࡽڦ႑ࡽԥഽፕᆩᇀ40 Ω࣍ୟୁۉॠ ֪ۉፆฉăᅺُLjC3ᆅগتᄲ൱ᅃ߲20 mV႑ࡽLjᅜඓԍ࣍ ୟዐ٪ሞ1 mAୁۉڦăᄲ൱ઠጲ20C15ڦHART႑ࡽVH ਏᆶᅜူປ३ဣຕă ഗॲฉڦΣ-Δ DACᆯᅃ߲ܾۙഗࠓׯLjഄࢫྺᅃ߲ Ⴤ้क़୳հഗăઠጲۙഗ߲ڇڦ࿋ୁ੦ጣᅃ߲ਸ࠲ۉ ୁᇸăࢫLjୁۉᇸᆯෙ߲ۉፆۉඹ୳հഗবႜ୳հ تă߲߳୳հഗব֑ᆩೌాۉፆLjෙ߲ۉඹሶᆌݴ՚ থC1ĂC2ࢅC3ᆅগăྺକፁHARTၹᅱ֫ڦᄲ ൱LjႴᄲᅃ߲ມटۅLjপኹೕ୲ྺ25 Hzگڦཚ୳հഗLj၎ ᆌۉڦඹC1ᆌྺ0.01 嘕FLjC2 = 0.5 嘕FLjC3 = 0.16 嘕FăHART ႑ࡽሶཚࡗবۅC3ڦتCCۉඹ᳘ࢇ࣍ڟୟዐăۉඹCCࢅ C3ኼሞඓԍइڥ1200 Hzࢅ2200 Hz HARTೕ୲้ڦೝ།ၚ ᆌă3๖ྺAD421ዐୁۉڦ੦ۉୟă 4k 12.5k ħCC = (20E–3 × C3)/(VH -20E – 3)ă ୳հഗ้क़ຕ= (CC + C3) (40E + 3)ă AD421 SIGMADELTA DAC ປ३ဣຕǖ20 mV/VH = CC /(CC + C3)ă BOOST ਉ૩ઠຫLjසࡕፕᆩᇀCCڦHART႑ࡽྺ500 mVރރ ኵLj୳հഗ้क़ຕႷܔᆌᇀ25 HzLjनHART႑ࡽټᄲ ൱LjሶCCᆌྺ6.2 nFፑᆸă 40k 80k 40 AD421-20C15থ੨ LOOP RTN LOOP( ) C1 C2 C3 CC C1 0.01 F C2 0.5 F C3 0.16 F FROM 20C15 3 AD421ୁۉ੦ۉୟ DACୁۉൻܾڼۯবLjन؊ٷݣୁۉړഗڦᅃ߲ሏݣ ࢅNPNৗ༹࠶LjᆩᅜยۨٗLOOP RTNᆅগୁୁۉڦă NPNৗ༹࠶ڦएटൻۉۯୟົޜᇀཚࡗ40 Ωॠ֪ۉፆۉڦ უLjᅜ๑ഄڪᇀথᇀDACᇑ࣍ୟኮक़ڦ80 kΩۉፆڦ ଇۉ܋უă 4๖ྺAD421-20C15থ੨ڦᅃዖೠࠚۉୟLjቛ๖କํ၄ ݀ พ থ ੨ Ⴔ ᄲ ߳ ڦዖ ፇ ॲ ă ྔ և ৗ ༹ ࠶ Q1(ࡼ ႙ MOSFET DN25D)ᇑAD421ాևሏ໙ٷݣഗࢅۉუएጚࠌཞ ႚׯᅃ߲࿘უഗLjཚࡗ࣍ୟۉუۙবAD421ۉۉࠃڦუă LK1ĂLK2ࢅLK3ሎႹॽۙবۉუՊྺײ5 VĂ3.3 Vई3 Vă ሺेྔևۙኝ࠶(Q2)ڦణڦইࡼگ႙MOSFET Q1ฉڦ ࠀ୲ሜă MOSFETྺAD421༵ࠃৢༀୁۉăAD421ฉڦBOOSTᆅগ ဌٗ࣍ୟୁࡗۙኝ࠶Q2ڦՂᄲୁۉLjᅜ๑ୁBOOST ୁۉڦᇑୁCOMৢڦༀୁۉኮࢅڪᇀยۨ࣍ڦୟୁۉă U3๖ྺ20C15 HARTۙۙഗᅜतํ၄HARTথ੨Ղ Ⴔڦ၎࠲ۉୟă᳘ࢇۉඹC15ॽHART႑ࡽ᳘ࢇAD421ڦ C3ᆅগڦتఇె4 mA–20 mA࣍ୟฉă Rev. A | Page 2 of 3 AN-534 LOOP PLUS J2-1 28F0195-100 L1 VCC Q1 D G C10 0.01 F REFOUT1 C B VCC C5 4.7 F Q2 BC548 E3297a–1–6/99 S C11 0.1 F E REFOUT2 BOOST C6 0.01 F LK3 CENTRONICS CONNECTOR R2 10k J1-3 U2A COMP LV DRIVE C7 2.2 F LK1 LATCH 74HC4050 R3 10k J1-5 C1 R1 1k U1 AD421 U2B 5 C8 0.1 F C1 0.01 F 2 3 REFIN C4 4.7 F LK2 4 C2 0.5 F CLOCK C2 C9 1nF 74HC4050 R4 10k J1-9 C3 0.16 F U2C 7 6 DATA 74HC4050 C3 COM LOOP RTN J1-18 LOOP MINUS J2-2 L2 J1-19 J1-20 28F0195-100 R14 732k J1-21 J1-22 J1-23 J1-25 C19 220pF C15 6.2nF C21 1000pF C20 1000pF R13 825k R12 216k R15 453k R10 787k 10 26 27 R18 1M 24 R17 1M 23 6 18 17 16 IRXAC ORXAF IRXA OTXA IAREF ORXD ICDREF ITXD 15 LK4 LK5 11 12 R8 14.7k U4 AD589 C18 0.01 F R7 200k U3 20C15 OXTL 19 INRTS VDD IXTL 20 XTAL1 460kHz C16 220pF VDDA OCBIAS 13 R16 402k VCC R9 10k OCD 22 VCC R11 3M C22 470pF VSS 21 14 9 8 7 5 1 R6 500k 4 AD421-20C15থ੨ۉୟ Rev. A | Page 3 of 3 C17 220pF PRINTED IN U.S.A. J1-24