AN-534: 采用20C15* HART调制解调器为路供电型4mA–20mA DAC AD421增添HART®性能 (Rev. A)

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* HARTۙ዆঴ۙഗྺ࣍ୟࠃ‫ۉ‬႙4 mA–20 mA DAC AD421ሺཁHART®Ⴀీ
ፕኁ;Albert O’Grady
०঻
AD421๟ᅃ੼ྜኝ‫ڦ‬ຕጴ๕࣍ୟࠃ‫ۉ‬4 mA–20 mAገ࣑ഗLj
ጆோኍ‫߾ܔ‬ᄽ੦዆ႜᄽ‫ڦ‬዇ీ݀พഗ዆ሰฆ‫ڦ‬༬ۨႴ൱ܸ
ยऺăፕྺᅃዖྜඇण‫ߛڦׯ‬৛‫܈‬Ă‫ׯگ‬Ԩ঴ਦ‫ݛ‬ӄLj޿
ഗॲ֑ᆩ৆ٙ႙16ᆅগ‫ހ‬ጎLj๟ᅜट‫ׯگ‬Ԩ༵ߛ዇ీ4 mA–20
mA݀พഗ‫ݴ‬Ր୲‫ڦ‬૙ၙኮ჋ăHART(੗ლ኷ᇺ‫ߌدײ‬ഗ
ߛ໏ཚ‫)ڢ‬ཚ႑ၹᅱሞᄽহԥ࠽‫ݘ‬থ๴Lj๟एᇀ዇ీ၄‫ׇ‬ᅏ
՗‫ڦ‬ຕጴሺഽ႙4 mA–20 mAཚ႑‫ڦ‬Քጚă޿ၹᅱ૧ᆩBell
202ೕᅎ॰੦(FSK)ՔጚLjॽ‫ۉگ‬ೝຕጴ႑ࡽ۠े‫ڟ‬4 mA–20
mAఇె႑ࡽฉăኄྺํ၄ଇዖཚ႑‫ݛ‬๕‫ظ‬ሰକཉॲLj๑
‫ࠕీڥ‬ሞዷᄲ‫ײࡗڦ‬Վଉኮྔሞ዇ీ၄‫ׇ‬ᅏ՗ઠ࣮‫ܮڿد‬
ྔ႑တăSymbios Logic‫؜‬೗‫ڦ‬SYM20C15ኼሞྺᆩࢽํ၄ᅃ
߲ग़ඹHART‫ڦ‬࿿૙֫‫ظ‬ሰཉॲă޿ഗॲཚࡗՂᄲ‫ۙڦ‬
዆Ă঴ۙĂሜհॠ֪Ăհႚႚ‫ټࢅׯ‬ཚ୳հॽ޿ၹᅱሞೌ
ฉํ၄ăHARTၹᅱ੗ሞփዐ܏4 mA–20 mA႑ࡽ‫ڦ‬൧઄ူ
৊ႜཚ႑Lj൐੗๑ዷऐᆌᆩ‫ײ‬Ⴞ(ዷऐ)௅௱ٗ၄‫ׇ‬ഗॲइ
‫ڥ‬ଇ߲ई߸‫߸ܠ‬ႎຕጴăᆯᇀຕጴFSK႑ࡽਏᆶ၎࿋૶Ⴤ
ႠLjᅺُփࣷ‫ܔ‬4 mA–20 mA႑ࡽሰ‫߅ׯ‬ඡăස཮2໯๖Ljܾ
৊዆‫ڦ‬1ࢅ0‫ݴ‬՚ᆩଇ߲փཞೕ୲1200 Hzࢅ2200 Hz‫پ‬՗ă
ኄၵຕጴ႑ࡽᅜ‫ۉگ‬ೝࢅೝ਩ኵྺଭ‫ڦ‬ኟ၀հ۠ेሞ኱ୁ
႑ࡽฉLjᅺُLj࿮ஃ၍ୟዐ๟‫݀ޏ‬ໃຕጴ႑ࡽLj‫ۼ‬փࣷᆶ
኱ୁ‫ݴ‬ଉ۠े‫ڟ‬၄ᆶ4 mA–20 mA႑ࡽฉăᅺُLj၄ᆶ‫ڦ‬ఇ
ెᅏ՗ධ੗ሞ֑ᆩHARTၹᅱ‫ڦ‬ဣཥዐኟ‫׉‬ሏႜǗᅺྺ‫گ‬
ཚ୳հഗ੗ၩ‫أ‬ຕጴ႑ࡽăᅃ߲‫ڇ‬ट‫ۅ‬10 Hz‫گ‬ཚ୳հഗ੗
ॽཚ႑႑ࡽᆶၳই‫گ‬዁ᅃ߲၎‫ړ‬ᇀ஢ଉ‫ײ‬႑ࡽ0.01%ፑᆸ
‫ڦ‬࿖հă཮2໯๖ྺ֑ᆩHARTၹᅱ‫ڦ‬၄‫ׇ‬ᅏ՗‫཮઀ڦ‬ă
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 LogicࠃऋLj૴ဣ‫ࣆۉ‬ǖ(408) 433-8000ă
HART๟HARTཚ႑एূࣷ‫ڦ‬ጀ֩ฆՔă
཮2 ዇ీ၄‫ׇ‬ᅏ՗
ԨᆌᆩԴऻዷᄲ‫ت‬૙࣍ୟࠃ‫ۉ‬႙4 mA–20 mA DAC AD421
ᇑ20C15 HARTۙ዆঴ۙഗኮक़‫ڦ‬থ੨࿚༶Ljཞ้༑༪ํ၄
ग़ඹHARTၹᅱ‫ڦ‬ᅏ՗໯Ⴔ‫ڦ‬Ղᄲօየă
AN-534
AD421‫ୁۉ‬੦዆‫ۉ‬ୟ
჋ስ᳘ࢇ‫ۉ‬ඹCC
AD421ాዃᅃ߲16-࿋Σ-Δ DACLjᆩᅜॽሜ෇๼෇໮٪ഗ‫ڦ‬
ຕጴ႑တገ࣑ྺ‫ୁۉ‬ăΣ-Δॐࠓ‫ݴ‬Ր୲ߛLjሞ‫ۙڇ‬Ⴀ‫ݛ‬௬
ਏᆶ‫ڥ‬ཀ‫ڦࢩ܀‬ᆫ๞Ljᆮഄ๢ᆩᇀ‫੻ټ‬ᄲ൱၎‫ܔ‬ড‫߾ڦگ‬
ᄽ੦዆࣍ৣăAD421੗ᅜԍኤ16࿋຤ೝ‫ۙڇڦ‬Ⴀă
࣍ୟฉ‫ڦ‬HART๼‫؜‬႑ࡽྺ1 mA‫ރރ‬ኵLjසമ໯ຎLjኄ੗ᅜ
ሞAD421ాևཚࡗၠC3ᆅগแेࢇ๢‫ۉڦ‬უ႑ࡽઠׂิă
HARTၹᅱཞ้ኧ‫׼‬ຕጴࢅఇెཚ႑LjᅺُLjጀ෇࣍ୟ‫ڦ‬
ຕጴHART႑ࡽփ‫߅ڥ‬ඡఇె࣍ୟ‫ڦୁۉ‬਩ኵLjኄᅃ‫ۅ‬ๆ
‫ݴ‬ዘᄲăHART႑ࡽ֑ᆩ঍ୁ᳘ࢇఇ๕LjᅜՆ௨ᆅഐ‫ٱ‬
ဃăCCࢅC3ଇ߲‫ۉ‬ඹ‫ܔ‬ઠጲ20C15‫ڦ‬HART‫ۉ‬უ႑ࡽ৊ႜ
ປ३‫ت‬૙LjᅜඓԍሞHART‫د‬๼ࡗ‫ײ‬ዐᆶᅃ߲1 mA‫ރރ‬ኵ‫ڦ‬
HART႑ࡽీ৊෇࣍ୟăC3ᆅগฉ‫ڦ‬႑ࡽፕᆩᇀᅃ߲40 kΩ
‫ۉ‬ፆฉLjଇԠᇀ޿႑ࡽ‫ڦ‬႑ࡽԥഽ዆ፕᆩᇀ40 Ω࣍ୟ‫ୁۉ‬ॠ
֪‫ۉ‬ፆฉăᅺُLjC3ᆅগ‫ت‬ᄲ൱ᅃ߲20 mV႑ࡽLjᅜඓԍ࣍
ୟዐ٪ሞ1 mA‫ୁۉڦ‬ăᄲ൱ઠጲ20C15‫ڦ‬HART๼෇႑ࡽVH
ਏᆶᅜူປ३ဣຕă
ഗॲฉ‫ڦ‬Σ-Δ DACᆯᅃ߲ܾ঩ۙ዆ഗࠓ‫ׯ‬Ljഄࢫྺᅃ߲૶
Ⴤ้क़୳հഗăઠጲۙ዆ഗ‫߲ڇڦ‬࿋ୁ੦዆ጣᅃ߲ਸ࠲‫ۉ‬
ୁᇸă඗ࢫLj޿‫ୁۉ‬ᇸᆯෙ߲‫ۉ‬ፆ‫ۉ‬ඹ୳հഗব৊ႜ୳հ
‫ت‬૙ă߲߳୳հഗব਩֑ᆩೌా‫ۉ‬ፆLjෙ߲‫ۉ‬ඹሶᆌ‫ݴ‬՚
૶থ዁C1ĂC2ࢅC3ᆅগăྺକ஢ፁHARTၹᅱ࿿૙֫‫ڦ‬ᄲ
൱LjႴᄲᅃ߲ມट‫ۅ‬Ljপኹೕ୲ྺ25 Hz‫گڦ‬ཚ୳հഗLj၎
ᆌ‫ۉڦ‬ඹC1ᆌྺ0.01 嘕FLjC2 = 0.5 嘕FLjC3 = 0.16 嘕FăHART
႑ࡽሶཚࡗব‫ۅ‬C3‫ڦت‬CC‫ۉ‬ඹ᳘ࢇ‫࣍ڟ‬ୟዐă‫ۉ‬ඹCCࢅ
C3ኼሞඓԍइ‫ڥ‬1200 Hzࢅ2200 Hz HARTೕ୲้‫ڦ‬ೝ།ၚ
ᆌă཮3໯๖ྺAD421ዐ‫ୁۉڦ‬੦዆‫ۉ‬ୟ઀཮ă
4k
12.5k
ħCC = (20E–3 × C3)/(VH -20E – 3)ă
୳հഗ้क़‫׉‬ຕ= (CC + C3) (40E + 3)ă
AD421
SIGMADELTA
DAC
ປ३ဣຕǖ20 mV/VH = CC /(CC + C3)ă
BOOST
ਉ૩ઠຫLjසࡕፕᆩᇀCC‫ڦ‬HART๼෇႑ࡽྺ500 mV‫ރރ‬
ኵLj൐୳հഗ้क़‫׉‬ຕႷ‫ܔ‬ᆌᇀ25 HzLjनHART႑ࡽ‫੻ټ‬ᄲ
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 AD421‫ୁۉ‬੦዆‫ۉ‬ୟ
DAC๼‫ୁۉ؜‬ൻ‫ܾڼۯ‬বLjन؊‫ٷݣୁۉړ‬ഗ‫ڦ‬ᅃ߲ሏ‫ݣ‬
ࢅNPNৗ༹࠶LjᆩᅜยۨٗLOOP RTNᆅগୁ‫ୁۉڦ؜‬ă
NPNৗ༹࠶‫ڦ‬एटൻ‫ۉۯ‬ୟົ‫ޜ‬ᇀཚࡗ40 Ωॠ֪‫ۉ‬ፆ‫ۉڦ‬
უLjᅜ๑ഄ‫ڪ‬ᇀ૶থᇀDAC๼‫؜‬ᇑ࣍ୟኮक़‫ڦ‬80 kΩ‫ۉ‬ፆ‫ڦ‬
ଇ‫ۉ܋‬უă
཮4໯๖ྺAD421-20C15থ੨‫ڦ‬ᅃዖೠࠚ‫ۉ‬ୟLjቛ๖କํ၄
݀ พ থ ੨ ໯ Ⴔ ᄲ ‫ ߳ ڦ‬ዖ ፇ ॲ ă ྔ և ৗ ༹ ࠶ Q1(ࡼ ৑ ႙
MOSFET DN25D)ᇑAD421ాևሏ໙‫ٷݣ‬ഗࢅ‫ۉ‬უएጚࠌཞ
ႚ‫ׯ‬ᅃ߲࿘უഗLjཚࡗ࣍ୟ‫ۉ‬უۙবAD421‫ۉۉࠃڦ‬უă
LK1ĂLK2ࢅLK3ሎႹॽ޿ۙব‫ۉ‬უՊ‫ྺײ‬5 VĂ3.3 Vई3 Vă
ሺेྔևۙኝ࠶(Q2)‫ڦ‬ణ‫ڦ‬๟ই‫ࡼگ‬৑႙MOSFET Q1ฉ‫ڦ‬
ࠀ୲޶ሜă
MOSFETྺAD421༵ࠃৢༀ‫ୁۉ‬ăAD421ฉ‫ڦ‬BOOSTᆅগ
ဌ๭ٗ࣍ୟୁࡗۙኝ࠶Q2‫ڦ‬Ղᄲ‫ୁۉ‬Ljᅜ๑ୁ෇BOOST
‫ୁۉڦ‬ᇑୁ෇COM‫ৢڦ‬ༀ‫ୁۉ‬ኮࢅ‫ڪ‬ᇀยۨ‫࣍ڦ‬ୟ‫ୁۉ‬ă
U3໯๖ྺ20C15 HARTۙ዆঴ۙഗᅜतํ၄HARTথ੨໯Ղ
Ⴔ‫ڦ‬၎࠲‫ۉ‬ୟă᳘ࢇ‫ۉ‬ඹC15ॽHART႑ࡽ᳘ࢇ዁AD421‫ڦ‬
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
Similar pages