Energy Metering with Integrated Oscillator ADE7757* this chip dir
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FEATURES On-Chip Oscillator Clock Source High Accuracy, Supposes Hz/60 521/1036 Less than 0.1% Error Over Dynamic Range ADE7757 Supplies Average Real Power Frequency Outputs High Frequency Output Intended Calibration Supplies Instantaneous Real Power Logic Output REVP Used Indicate Potential Miswiring Negative Power Direct Drive Electromechanical Counters Phase Stepper Motors Proprietary ADCs Provide High Accuracy over Large Variations Environmental Conditions Time On-Chip Power Supply Monitoring On-Chip Creep Protection Load Threshold) On-Chip Reference ppm/ Typical) with External Overdrive Capability Single Supply, Power Typical) Cost CMOS Process Input only GENERAL DESCRIPTION
Energy Metering with Integrated Oscillator ADE7757*
this chip directly interfaces with shunt resistor operates only with input. ADE7757 specifications surpass accuracy requirements quoted IEC1036 standard. similarity between ADE7757 AD7755, Application Note AN-559 used basis description IEC1036 cost watt-hour meter reference design. only analog circuitry used ADE7757 sigmadelta ADCs reference circuit. other signal processing (e.g., multiplication filtering) carried digital domain. This approach provides superior stability accuracy over time extreme environmental conditions. ADE7757 supplies average real power information frequency outputs These outputs used directly drive electromechanical counter interface with MCU. high frequency logic output, ideal calibration purposes, provides instantaneous real power information. ADE7757 includes power supply monitoring circuit supply pin. ADE7757 will remain inactive until supply voltage reaches approximately supply falls below ADE7757 will also remain inactive outputs will their nonactive modes. Internal phase matching circuitry ensures that voltage current channels phase matched while current channel eliminates offsets. internal no-load threshold ensures that ADE7757 does exhibit creep when load present. ADE7757 available 16-lead SOIC narrow-body package.
FUNCTIONAL BLOCK DIAGRAM
AGND DGND
ADE7757 high accuracy electrical energy measurement reduction version AD7755 with enhancement precise oscillator circuit that serves clock source chip. ADE7757 eliminates cost external crystal resonator, thus reducing overall cost meter built with
ADE7757
POWER SUPPLY MONITOR .110101. MULTIPLIER PHASE CORRECTION .11011001. SIGNAL PROCESSING BLOCK
2.5V REFERENCE
INTERNAL OSCILLATOR
DIGITAL-TO-FREQUENCY CONVERTER
REFIN/OUT
RCLKIN
REVP
*U.S. Patents 5,745,323, 5,760,617, 5,862,069, 5,872,469; others pending.
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Information furnished Analog Devices believed accurate reliable. However, responsibility assumed Analog Devices use, infringements patents other rights third parties that result from use. license granted implication otherwise under patent patent rights Analog Devices.
Technology Way, P.O. 9106, Norwood, 02062-9106, USA. Tel: 781/329-4700 www.analog.com Fax: 781/326-8703 Analog Devices, Inc., 2002
ADE7757-SPECIFICATIONS 0.1%
Parameter ACCURACY Measurement Error1 Channel Phase Error1 Between Channels Phase Lead Capacitive) Phase Inductive) Power Supply Rejection1 Output Frequency Variation (CF) Power Supply Rejection1 Output Frequency Variation (CF) ANALOG INPUTS Channel Maximum Signal Level Channel Maximum Signal Level Input Impedance (DC) Bandwidth Offset Error1, Gain Error1 OSCILLATOR FREQUENCY (OSC) Oscillator Frequency Tolerance1 Oscillator Frequency Stability1 REFERENCE INPUT REFIN/OUT Input Voltage Range Input Capacitance ON-CHIP REFERENCE Reference Error Temperature Coefficient LOGIC INPUTS3 SCF, Input High Voltage, VINH Input Voltage, VINL Input Current, Input Capacitance, LOGIC OUTPUTS3 Output High Voltage, Output Voltage, Output High Voltage, Output Voltage, Frequency Output Error1, (CF) POWER SUPPLY
(VDD AGND DGND On-Chip Reference, RCKLIN 15ppm/ TMIN TMAX unless otherwise noted.)
Value Unit Test Conditions/Comments Channel with Full-Scale Signal mV), 25°C Over Dynamic Range Line Frequency
Reading
Degrees(°) Degrees(°) Reading 21.2 rms, 116.7 Ripple 21.2 rms, 116.7 rms, Analog Inputs section AGND AGND kHz, RCKLIN 0.1% 15ppm/°C kHz, RCKLIN 0.1% 15ppm/°C Terminology Section Typical Performance Characteristics. External Reference 21.2 rms, 116.7 RCKLIN 0.1% 15ppm/°C
Reading
nominal Ideal nominal Reading ppm/°C ppm/°C
Nominal
Typically
ISOURCE ISINK ISOURCE ISINK External Reference, 21.2 rms, 116.7 Specified Performance Typically
Ideal
4.75 5.25
NOTES Terminology section explanation specifications. plots Typical Performance Characteristics. Sample tested during initial release after redesign process change that affect this parameter. Specifications subject change without notice.
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ADE7757 TIMING CHARACTERISTICS1, 0.1%
Parameter t43,
(VDD AGND DGND On-Chip Reference, RCKLIN 15ppm/ TMIN TMAX unless otherwise noted.)
Unit Test Conditions/Comments Pulsewidth (Logic Low) Output Pulse Period. Transfer Function section. Time between Falling Edge Falling Edge Pulsewidth (Logic High) Pulse Period. Transfer Function section. Minimum Time between Pulse
Versions Table Table
NOTES Sample tested during initial release after redesign process change that affect this parameter Figure pulsewidths fixed higher output frequencies. Frequency Outputs section. pulse always high frequency mode. Frequency Outputs section Table III. Specifications subject change without notice.
Figure Timing Diagram Frequency Outputs
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ADE7757
ABSOLUTE MAXIMUM RATINGS
25°C, unless otherwise noted.)
Power Supply Rejection
AGND -0.3 DGND -0.3 Analog Input Voltage AGND V1P, V1N, V2P, Reference Input Voltage AGND -0.3 Digital Input Voltage DGND -0.3 Digital Output Voltage DGND -0.3 Operating Temperature Range Industrial Versions) -40°C +85°C Storage Temperature Range -65°C +150°C Junction Temperature 150°C 16-Lead Plastic SOIC, Power Dissipation Thermal Impedance 124.9°C/W Lead Temperature, Soldering Vapor Phase sec) 215°C Infrared sec) 220°C
This quantifies ADE7757 measurement error percentage reading when power supplies varied. measurement, reading nominal supplies taken. rms/100 signal then introduced onto supplies second reading obtained under same input signal levels. error introduced expressed percentage reading-see Measurement Error definition. measurement, reading nominal supplies taken. supplies then varied second reading obtained with same input signal levels. error introduced again expressed percentage reading.
Offset Error
This refers small signal (offset) associated with analog inputs ADCs. However, Channel eliminates offset circuitry. Therefore, power calculation affected this offset.
Frequency Output Error (CF)
Stresses above those listed under Absolute Maximum Ratings cause permanent damage device. This stress rating only; functional operation device these other conditions above those listed operational sections this specification implied. Exposure absolute maximum rating conditions extended periods affect device reliability. JEDEC Standard (2-layer) Board
ORDERING GUIDE
frequency output error ADE7757 defined difference between measured output frequency (minus offset) ideal output frequency. difference expressed percentage ideal frequency. ideal frequency obtained from ADE7757 transfer function (see Transfer Function section).
Gain Error
Model ADE7757ARN ADE7757ARNRL
Package Description Package Options RN-16 RNRL-16 Evaluation Board
SOIC Narrow-Body SOIC Narrow-Body Reel EVAL-ADE7757EB Evaluation Board
TERMINOLOGY Measurement Error
gain error ADE7757 defined difference between measured output frequency (minus offset) ideal output frequency. difference expressed percentage ideal frequency. ideal frequency obtained from ADE7757 transfer function (see Transfer Function section).
Oscillator Frequency Tolerance
error associated with energy measurement made ADE7757 defined following formula:
%Error Energy registered 7757 True Energy 100% True Energy
oscillator frequency tolerance ADE7757 defined part-to-part frequency variation terms percentage room temperature (25°C). measured taking difference between measured oscillator frequency nominal frequency defined Specifications section.
Oscillator Frequency Stability
Phase Error Between Channels
(High-Pass Filter) current channel (Channel phase lead response. offset this phase response equalize phase response between channels, phase correction network also placed Channel phase correction network matches phase within ±0.1° over range 0.2° over range kHz. Figures
Oscillator frequency stability defined frequency variation terms percentage drift million over operating temperature range. metering application, temperature range -40°C +85°C. Oscillator frequency stability measured taking difference between measured oscillator frequency -40°C +85°C measured oscillator frequency +25°C.
CAUTION (electrostatic discharge) sensitive device. Electrostatic charges high 4000 readily accumulate human body test equipment discharge without detection. Although ADE7757 features proprietary protection circuitry, permanent damage occur devices subjected high energy electrostatic discharges. Therefore, proper precautions recommended avoid performance degradation loss functionality.
WARNING!
SENSITIVE DEVICE
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ADE7757
CONFIGURATION
DGND VIEW (Not Scale) REVP RCLKIN AGND
ADE7757
REFIN/OUT
FUNCTION DESCRIPTIONS
Mnemonic
Description Power Supply. This provides supply voltage circuitry ADE7757. supply voltage should maintained specified operation. This should decoupled with capacitor parallel with ceramic capacitor. Analog Inputs Channel (voltage channel). These inputs provide fully differential input pair. maximum differential input voltage specified operation. Both inputs have internal protection circuitry; overvoltage sustained these inputs without risk permanent damage. Analog Inputs Channel (current channel). These inputs fully differential voltage inputs with maximum signal level with respect specified operation. Both inputs have internal protection circuitry and, addition, overvoltage sustained these inputs without risk permanent damage. This provides ground reference analog circuitry ADE7757, i.e., ADCs reference. This should tied analog ground plane PCB. analog ground plane ground reference analog circuitry, e.g., antialiasing filters, current voltage sensors, forth. accurate noise suppression, analog ground plane should only connected digital ground plane point. star ground configuration will help keep noisy digital currents away from analog circuits. This provides access on-chip voltage reference. on-chip reference nominal value typical temperature coefficient ppm/°C. external reference source also connected this pin. either case, this should decoupled AGND with tantalum capacitor ceramic capacitor. internal reference cannot used drive external load. Select Calibration Frequency. This logic input used select frequency calibration output Table shows calibration frequencies selection. These logic inputs used select four possible frequencies digital-to-frequency conversion. With this logic input, designers have greater flexibility when designing energy meter. Selecting Frequency Energy Meter Application section. enable internal oscillator clock source chip, precise temperature drift resistor nominal value must connected from this DGND. This logic output will high when negative power detected, i.e., when phase angle between voltage current signals greater than 90°. This output latched will reset when positive power once again detected. output will high same time pulse issued This provides ground reference digital circuitry ADE7757, i.e., multiplier, filters, digital-to-frequency converter. This should tied digital ground plane PCB. digital ground plane ground reference digital circuitry, e.g., counters (mechanical digital), MCUs, indicator LEDs. accurate noise suppression, analog ground plane should connected digital ground plane point only, e.g., star ground. Calibration Frequency Logic Output. logic output provides instantaneous real power information. This output intended calibration purposes. Also description. Frequency Logic Outputs. supply average real power information. logic outputs used directly drive electromechanical counters phase stepper motors. Transfer Function section.
V2P,
V1N,
AGND
REFIN/OUT
RCLKIN REVP
DGND
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ADE7757-Typical Performance Characteristics
100nF 602k 220V 150nF 40mA 150nF REVP 150nF 150nF REFIN/OUT 100nF AGND DGND 10nF 10nF 10nF RCLKIN 6.2k PS2501-1
ADE7757
Figure Test Circuit Performance Curves
ERROR -0.1 -0.2 -0.3 -0.4 -0.5 0.01 ERROR ON-CHIP REFERENCE
EXTERNAL REFERENCE -0.2 -0.4 -0.6 -0.8 -1.0 0.01
CURRENT
CURRENT
Error Reading over Temperature with On-Chip Reference
Error Reading over Temperature with External Reference
ON-CHIP REFERENCE
EXTERNAL REFERENCE
ERROR
ERROR
-0.1 -0.3 -0.5 0.01
-0.2 -0.4 -0.6 -0.8 -1.0 0.01
CURRENT
CURRENT
Error Reading over Temperature with On-Chip Reference 0.5)
Error Reading over Temperature with External Reference 0.5)
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ADE7757
+0.5 -0.5 +1.0 -0.1 -0.2 -0.3 -0.4 -0.5 FREQUENCY DISTRIBUTION CHARACTERISTICS NUMBER POINTS: INTERNAL REFERENCE MINIMUM: -4.319 TEMPERATURE MAXIMUM: 2.2828 MEAN: -1.04576552 STD. DEV: 1.300956604
ERROR
Error Reading over Input Frequency
Channel Offset Distribution
ERROR
ON-CHIP REFERENCE
DISTRIBUTION CHARACTERISTICS NUMBER POINTS: MINIMUM: -9.82923 INTERNAL REFERENCE MAXIMUM: 0.472126 TEMPERATURE MEAN: 4.54036589 STD. DEV: 1.89694475
5.25V
5.0V
-0.2 -0.4 -0.6 -0.8 -1.0 0.01 4.75V
CURRENT
with Internal Reference
Channel Offset Distribution
EXTERNAL REFERENCE
DISTRIBUTION CHARACTERISTICS NUMBER POINTS: EXTERNAL REFERENCE MINIMUM: -6.15% TEMPERATURE MAXIMUM: 9.96% MEAN: STD. DEV: 2.84%
5.25V
ERROR
5.0V -0.2 4.75V -0.4 -0.6 -0.8 -1.0 0.01
CURRENT
with External Reference
Part-to-Part Distribution From Mean
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ADE7757
THEORY OPERATION
ADCs digitize voltage signals from current voltage sensors. These ADCs 16-bit sigma-delta with oversampling rate kHz. This analog input structure greatly simplifies sensor interfacing providing wide dynamic range direct connection sensor also simplifies antialiasing filter design. high-pass filter current channel removes component from current signal. This eliminates inaccuracies real power calculation offsets voltage current signals. Because always enabled, will operate only with input (see Offset Effects section). real power calculation derived from instantaneous power signal. instantaneous power signal generated direct multiplication current voltage signals. order extract real power component (i.e., component), instantaneous power signal low-pass filtered. Figure illustrates instantaneous real power signal shows real power information extracted low-pass filtering instantaneous power signal. This scheme correctly calculates real power sinusoidal current voltage waveforms power factors. signal processing carried digital domain superior stability over temperature time.
MULTIPLIER DIGITAL-TOFREQUENCY DIGITAL-TOFREQUENCY
frequency outputs (F1, ADE7757 generated accumulating this real power information. This frequency inherently means long accumulation time between output pulses. Consequently, resulting output frequency proportional average real power. This average real power information then accumulated (e.g., counter) generate real energy information. Conversely, high output frequency hence shorter integration time, output frequency proportional instantaneous real power. This useful system calibration, which done faster under steady load conditions.
Power Factor Considerations
method used extract real power information from instantaneous power signal (i.e., low-pass filtering) still valid even when voltage current signals phase. Figure displays unity power factor condition (Displacement Power Factor) 0.5, i.e., current signal lagging voltage 60°. assume voltage current waveforms sinusoidal, real power component instantaneous power signal (i.e., term) given
cos(60°)
This correct real power calculation.
INSTANTANEOUS POWER SIGNAL POWER INSTANTANEOUS REAL POWER SIGNAL
INSTANTANEOUS POWER SIGNAL p(t)
INSTANTANEOUS REAL POWER SIGNAL
CURRENT VOLTAGE POWER INSTANTANEOUS POWER SIGNAL INSTANTANEOUS REAL POWER SIGNAL
TIME
TIME
TIME
Figure Signal Processing Block Diagram
TIME
VOLTAGE
CURRENT
Figure Component Instantaneous Power Signal Conveys Real Power Information
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ADE7757
Nonsinusoidal Voltage Current
real power calculation method also holds true nonsinusoidal current voltage waveforms. voltage current waveforms practical applications will have some harmonic content. Using Fourier Transform, instantaneous voltage current waveforms expressed terms their harmonic content.
ANALOG INPUTS Channel (Current Channel)
voltage output from current sensor connected ADE7757 here. Channel fully differential voltage input. positive input with respect V1N. maximum peak differential signal Channel should less than pure sinusoidal signal) specified operation.
+30mV DIFFERENTIAL INPUT 30mV PEAK COMMON-MODE 6.25mV -30mV
sin(ht
where: v(t) instantaneous voltage average value value voltage harmonic phase angle voltage harmonic.
sin(ht
AGND
where: i(t)
Figure Maximum Signal Levels, Channel
instantaneous current component value current harmonic phase angle current harmonic.
Using Equations real power expressed terms fundamental real power (P1) harmonic real power (PH).
diagram Figure illustrates maximum signal levels V1N. maximum differential voltage differential voltage signal inputs must referenced common mode, e.g., AGND. maximum commonmode signal 6.25 shown Figure
Channel (Voltage Channel
where:
output line voltage sensor connected ADE7757 this analog input. Channel fully differential voltage input with maximum peak differential signal Figure illustrates maximum signal levels that connected ADE7757 Channel
+165mV DIFFERENTIAL INPUT 165mV PEAK COMMON-MODE 25mV
-165mV
AGND
Figure Maximum Signal Levels, Channel
seen from Equation harmonic real power component generated every harmonic, provided that harmonic present both voltage current waveforms. power factor calculation previously been shown accurate case pure sinusoid. Therefore harmonic real power must also correctly account power factor since made series pure sinusoids. Note that input bandwidth analog inputs nominal internal oscillator frequency kHz.
Channel usually driven from common-mode voltage, i.e., differential voltage signal input referenced common mode (usually AGND). analog inputs ADE7757 driven with common-mode voltages with respect AGND. However best results achieved using common mode equal AGND.
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ADE7757
Typical Connection Diagrams
Figure shows typical connection diagram Channel shunt current sensor selected this example because cost compared other current sensors such (current transformer). This ideal current meters.
SHUNT 30mV AGND PHASE NEUTRAL
TIME
INTERNAL ACTIVATION INACTIVE
ACTIVE
INACTIVE
Figure Typical Connection Channel
Figure On-Chip Power Supply Monitor
Offset Effects
Figure shows typical connection Channel Typically, ADE7757 biased around neutral wire, resistor divider used provide voltage signal that proportional line voltage. Adjusting ratio also convenient carrying gain calibration meter.
165mV
PHASE NEUTRAL
Figure illustrates effect offsets real power calculation. seen, offsets Channel Channel will contribute component after multiplication. Since this component extracted used generate real power information, offsets will contribute constant error real power calculation. This problem easily avoided built-in Channel removing offsets from least channel, error component generated multiplication. Error terms line frequency removed digital-to-frequency conversion (see Digital-to-Frequency Conversion section). equation below shows power calculation affected offsets current voltage channels:
Figure Typical Connections Channel
POWER SUPPLY MONITOR
ADE7757 contains on-chip power supply monitor. power supply (VDD) continuously monitored ADE7757. supply less than ADE7757 becomes inactive. This useful ensure proper device operation power-up power-down. power supply monitor built hysteresis filtering that provide high degree immunity false triggering from noisy supplies. seen from Figure trigger level nominally tolerance this trigger level within power supply decoupling part should such that ripple does exceed specified normal operation.
cos(t cos(t
cos(t cos(t cos(2t
COMPONENT (INCLUDING ERROR TERM) EXTRACTED REAL POWER CALCULATION
FREQUENCY RAD/s
Figure Effect Channel Offset Real Power Calculation
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ADE7757
Channel associated phase response that compensated on-chip. Figures show phase error between channels with compensation network activated. ADE7757 phase compensated shown. This will ensure correct active harmonic power calculation even power factors.
0.30 0.25 0.20
PHASE Degrees
line frequency this would give attenuation (100 component approximately dominating harmonic will twice line frequency instantaneous power calculation. Figure shows instantaneous real power signal output that still contains significant amount instantaneous power information, i.e., cos(2t). This signal then passed digital-to-frequency converter where integrated (accumulated) over time order produce output frequency. accumulation signal will suppress average non-dc components instantaneous real power signal. average value sinusoidal signal zero. Thus frequency generated ADE7757 proportional average real power. Figure shows digitalto-frequency conversion steady load conditions, i.e., constant voltage current.
FREQUENCY
0.15 0.10 0.05 -0.05 -0.10 1000 FREQUENCY
MULTIPLIER
DIGITAL-TOFREQUENCY DIGITAL-TOFREQUENCY EXTRACT REAL POWER TERM)
TIME
FREQUENCY
Figure Phase Error between Channels kHz)
0.30 0.25 0.20
PHASE Degrees
ATTENUATED
TIME
0.15 0.10 0.05 -0.05 -0.10
FREQUENCY (RAD/s) INSTANTANEOUS REAL POWER SIGNAL (FREQUENCY DOMAIN)
Figure Real Power-to-Frequency Conversion
FREQUENCY
Figure Phase Error between Channels
DIGITAL-TO-FREQUENCY CONVERSION
previously described, digital output low-pass filter after multiplication contains real power information. However, since this ideal "brick wall" filter implementation, output signal also contains attenuated components line frequency harmonics, i.e., cos(hwt) where magnitude response filter given
4.452
seen diagram, frequency output seen vary over time, even under steady load conditions. This frequency variation primarily cos(2t) component instantaneous real power signal. output frequency 2048 times higher than frequency This higher output frequency generated accumulating instantaneous real power signal over much shorter time while converting frequency. This shorter accumulation period means less averaging cos(2t) component. Consequently, some this instantaneous power signal passes through digital-to-frequency conversion. This will problem application. Where used calibration purposes, frequency should averaged frequency counter, which will remove ripple. being used measure energy, example microprocessor-based application, output should also averaged calculate power. Because outputs operate much lower frequency, more averaging instantaneous real power signal carried out. result greatly attenuated sinusoidal content virtually ripple-free frequency output.
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ADE7757
Interfacing ADE7757 Microcontroller Energy Measurement INTERNAL OSCILLATOR (OSC)
easiest interface ADE7757 microcontroller high frequency output with output frequency scaling 2048 This done setting (see Table III). With full-scale signals analog inputs, output frequency will approximately 2.867 kHz. Figure illustrates scheme that could used digitize output frequency carry necessary averaging mentioned previous section.
FREQUENCY RIPPLE AVERAGE FREQUENCY
nominal internal oscillator frequency when used with RCKLIN with nominal value frequency outputs directly proportional oscillator frequency, thus RCKLIN must have tolerance temperature drift ensure stability linearity chip. oscillator frequency inversely proportional RCKLIN shown Figure Although internal oscillator operates when used with RCKLIN values between recommended choose value within range nominal value shown Figure
FREQUENCY
TIME COUNTER
ADE7757
TIMER
RESISTANCE
Figure Interfacing ADE7757
shown, frequency output connected counter port. This will count number pulses given integration time, which determined internal timer. average power proportional average frequency given Counter Average Frequency Average Power Time
energy consumed during integration period given
Figure Effect RCKLIN Internal Oscillator Frequency (OSC)
TRANSFER FUNCTION Frequency Outputs
Energy Average Power Time
Counter Time Counter Time
purpose calibration, this integration time could seconds order accumulate enough pulses ensure correct averaging frequency. normal operation, integration time could reduced seconds depending, example, required update rate display. With shorter integration times MCU, amount energy each update still have some small amount ripple, even under steady load conditions. However, over minute more measured energy will have ripple.
Power Measurement Considerations
ADE7757 calculates product voltage signals Channel Channel then low-pass filters this product extract real power information. This real power information then converted frequency. frequency information output form active pulses. pulse rate these outputs relatively low, e.g., 0.175 maximum signals with 0-see Table This means that frequency these outputs generated from real power information accumulated over relatively long period time. result output frequency that proportional average real power. averaging real power signal implicit digital-to-frequency conversion. output frequency pulse rate related input voltage signals following equation:
Freq
where: Freq V1rms V2rms Vref F1-4
515.84 1rms 2rms F1-4 Vref
Calculating displaying power information will always have some associated ripple that will depend integration period used determine average power, also load. example, light loads output frequency With integration period seconds, only about pulses will counted. possibility missing pulse always exists ADE7757 output frequency running asynchronously timer. This would result one-in-twenty error power measurement.
Output frequency (Hz) Differential voltage signal Channel (volts) Differential voltage signal Channel (volts) reference voltage (2.5 (volts) four possible frequencies selected using logic inputs S1-see Table
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ADE7757
Table F1-4 Frequency Selection Table III. Maximum Output Frequency
Relation1 OSC/219 OSC/218 OSC/217 OSC/216
F1-4 nominal OSC(Hz)2 0.86 1.72 3.44 6.86
Signals (Hz)* 22.4 11.2 22.4 11.2 22.4 11.2 22.4 2048 2.867
F1-4 binary fraction internal oscillator frequency (OSC). Values generated using nominal frequency kHz.
Example
this example, with voltages peak applied peak applied expected output frequency calculated follows: F1-4 V1rms V2rms Vref OSC/2 0.03/2 0.165/2 (nominal reference value). NOTE: on-chip reference used, actual output frequencies vary from device device reference tolerance
Freq 515.85 0.03 0.165 2.52 0.204 0.175
*Values generated using nominal frequency
SELECTING FREQUENCY ENERGY METER APPLICATION
shown Table user select four frequencies. This frequency selection determines maximum frequency These outputs intended driving energy register (electromechanical others). Since only four different output frequencies selected, available frequency selection been optimized meter constant imp/kWhr with maximum current between Table shows output frequency several maximum currents (IMAX) with line voltage cases, meter constant imp/kWhr.
Table Frequency imp/kWhr
Table Maximum Output Frequency
IMAX Relation 0.204 0.204 0.204 0.204 Frequency* Inputs (Hz) 0.175 0.35 0.70 1.40 12.5 25.0 40.0 60.0 80.0 120.0
(Hz) 0.076 0.153 0.244 0.367 0.489 0.733
*Values generated using nominal frequency
Frequency Output
pulse output (Calibration Frequency) intended calibration purposes. output pulse rate 2048 times pulse rate lower F1-4 frequency selected, higher scaling (except high frequency mode Table shows frequencies related, depending states logic inputs SCF. relatively high pulse rate, frequency logic output proportional instantaneous real power. with derived from output low-pass filter after multiplication. However, because output frequency high, this real power information accumulated over much shorter time. Therefore less averaging carried digital-to-frequency conversion. With much less averaging real power signal, output much more responsive power fluctuations (see Signal Processing Block Figure
F1-4 frequencies allow complete coverage this range output frequencies (F1, F2). When designing energy meter, nominal design voltage Channel (voltage) should half-scale allow calibration meter constant. current channel should also more than half-scale when meter sees maximum load. This will allow overcurrent signals signals with high crest factors accommodated. Table shows output frequency when both analog inputs half-scale. frequencies listed Table align very well with those listed Table maximum load.
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ADE7757
Table Frequency with Half-Scale Inputs
Frequency F1-4 (Hz)* Half-Scale Input* 0.86 1.72 3.44 6.86 0.051 0.051 0.051 0.051 0.044 0.088 0.176 0.352
pulsewidth half period. example, frequency pulsewidth NOTE: When high frequency mode selected, (i.e., pulsewidth fixed Therefore will always regardless output frequency
LOAD THRESHOLD
*Values generated using nominal frequency
When selecting suitable F1-4 frequency meter design, frequency output IMAX (maximum load) with meter constant imp/kWhr should compared with column four Table closest frequency Table will determine best choice frequency (F1-4). example, meter with maximum current being designed, output frequency with meter constant imp/kWhr 0.153 (from Table IV). Looking Table closest frequency 0.153 column four 0.176 Therefore, (3.44 Hz-see Table selected this design.
Frequency Outputs
Figure shows timing diagram various frequency outputs. outputs frequency outputs that used directly drive stepper motor electromechanical impulse counter. outputs provide alternating frequency pulses. pulsewidths (t1) such that falls below 1062 (0.942 they half their period. maximum output frequencies shown Table high frequency output intended used communications calibration purposes. produces mswide active high pulse (t4) frequency proportional active power. output frequencies given Table III. case period (t5) falls below
ADE7757 also includes "no-load threshold" "startup current" feature that will eliminate creep effects meter. ADE7757 designed issue minimum output frequency. load generating frequency lower than this minimum frequency will cause pulse issued minimum output frequency given 0.0014% full-scale output frequency each F1-4 frequency selections (see Table example, energy meter with meter constant imp/kWhr using (3.44 Hz), minimum output frequency would 0.0014% 3.44 4.81 10-5 This would 3.08 10-3 when this example, no-load threshold would equivalent load start-up current Compare this value IEC1036 specification which states that meter must start with load equal less than 0.4% (Ib) meter, 0.4% equivalent
NEGATIVE POWER INFORMATION
ADE7757 detects when current voltage channels have phase shift greater than 90°. This mechanism detect wrong connection meter generation negative power. REVP output will active high when negative power detected active positive power detected. REVP output changes state pulse issued REVP functional current version will only work version (ADE7757A).
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ADE7757
OUTLINE DIMENSIONS 16-Lead Standard Small Outline Package Narrow Body (RN-16)
Dimensions shown millimeters (inches)
10.00 (0.3937) 9.80 (0.3858)
4.00 (0.1575) 3.80 (0.1496)
6.20 (0.2441) 5.80 (0.2283)
1.27 (0.0500) 0.25 (0.0098) 0.10 (0.0039)
1.75 (0.0689) 1.35 (0.0531)
0.50 (0.0197) 0.25 (0.0098)
0.51 (0.0201) SEATING 0.25 (0.0098) 1.27 (0.0500) 0.33 (0.0130) PLANE 0.40 (0.0157) 0.19 (0.0075) CONTROLLING DIMENSIONS MILLIMETERS; INCH DIMENSIONS PARENTHESES) ROUNDED-OFF MILLIMETER EQUIVALENTS REFERENCE ONLY APPROPRIATE DESIGN COMPLIANT JEDEC STANDARDS MS-012AC
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C02898-0-8/02(0)
PRINTED U.S.A.
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