ADE7757ARNZ [ADI]

Single Phase Energy Metering IC with Integrated Oscillator;
ADE7757ARNZ
型号: ADE7757ARNZ
厂家: ADI    ADI
描述:

Single Phase Energy Metering IC with Integrated Oscillator

光电二极管
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中文:  中文翻译
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Energy Metering IC  
with Integrated Oscillator  
ADE7757*  
FEATURES  
On-Chip Oscillator as Clock Source  
built with this IC. The chip directly interfaces with the shunt  
resistor and operates only with ac input.  
High Accuracy, Supposes 50 Hz/60 Hz IEC 521/IEC 61036  
Less than 0.1% Error over a Dynamic Range of 500 to 1  
The ADE7757 Supplies Average Real Power on the  
Frequency Outputs F1 and F2  
The ADE7757 specifications surpass the accuracy requirements  
as quoted in the IEC 61036 standard. The AN-679 Application  
Note can be used as a basis for a description of an IEC 61036  
low cost watt-hour meter reference design.  
The High Frequency Output CF Is Intended for  
Calibration and Supplies Instantaneous Real Power  
The Logic Output REVP Can Be Used to Indicate a  
Potential Miswiring or Negative Power  
Direct Drive for Electromechanical Counters and  
2-Phase Stepper Motors (F1 and F2)  
Proprietary ADCs and DSP Provide High Accuracy over  
Large Variations in Environmental Conditions and  
Time  
The only analog circuitry used in the ADE7757 is in the -⌬  
ADCs and reference circuit. All other signal processing (e.g.,  
multiplication and filtering) is carried out in the digital domain.  
This approach provides superior stability and accuracy over  
time and extreme environmental conditions.  
The ADE7757 supplies average real power information on the  
low frequency outputs F1 and F2. These outputs may be used  
to directly drive an electromechanical counter or interface with  
an MCU. The high frequency CF logic output, ideal for calibra-  
tion purposes, provides instantaneous real power information.  
On-Chip Power Supply Monitoring  
On-Chip Creep Protection (No Load Threshold)  
On-Chip Reference 2.5 V (20 ppm/C Typical)  
with External Overdrive Capability  
Single 5 V Supply, Low Power (20 mW Typical)  
Low Cost CMOS Process  
The ADE7757 includes a power supply monitoring circuit on  
the VDD supply pin. The ADE7757 will remain inactive until  
the supply voltage on VDD reaches approximately 4 V. If the  
supply falls below 4 V, the ADE7757 will also remain inactive  
and the F1, F2, and CF outputs will be in their nonactive modes.  
AC Input Only  
GENERAL DESCRIPTION  
Internal phase matching circuitry ensures that the voltage and  
current channels are phase matched while the HPF in the cur-  
rent channel eliminates dc offsets. An internal no-load threshold  
ensures that the ADE7757 does not exhibit creep when no load  
is present.  
The ADE7757 is a high accuracy electrical energy measurement  
IC. It is a pin reduction version of the ADE7755 with an enhance-  
ment of a precise oscillator circuit that serves as a clock source  
to the chip. The ADE7757 eliminates the cost of an external  
crystal or resonator, thus reducing the overall cost of a meter  
The ADE7757 is available in a 16-lead SOIC narrow-body package.  
FUNCTIONAL BLOCK DIAGRAM  
V
AGND  
DGND  
DD  
ADE7757  
POWER  
SUPPLY MONITOR  
SIGNAL  
PROCESSING  
BLOCK  
V2P  
V2N  
...110101...  
-ꢃ  
ADC  
MULTIPLIER  
LPF  
PHASE  
CORRECTION  
HPF  
...11011001...  
V1N  
V1P  
-ꢃ  
ADC  
DIGITAL-TO-FREQUENCY  
CONVERTER  
INTERNAL  
OSCILLATOR  
4kꢁ  
2.5V  
REFERENCE  
REF  
IN/OUT  
RCLKIN  
REVP CF  
F1  
S0  
SCF  
S1  
F2  
*U.S. Patents 5,745,323; 5,760,617; 5,862,069; 5,872,469.  
REV. A  
Information furnished by Analog Devices is believed to be accurate and  
reliable. However, no responsibility is assumed by Analog Devices for its  
use, norforanyinfringementsofpatentsorotherrightsofthirdpartiesthat  
may result from its use. No license is granted by implication or otherwise  
under any patent or patent rights of Analog Devices. Trademarks and  
registered trademarks are the property of their respective owners.  
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.  
Tel: 781/329-4700  
Fax: 781/326-8703  
www.analog.com  
© 2003 Analog Devices, Inc. All rights reserved.  
ADE7757* PRODUCT PAGE QUICK LINKS  
Last Content Update: 02/23/2017  
COMPARABLE PARTS  
View a parametric search of comparable parts.  
DESIGN RESOURCES  
ADE7757 Material Declaration  
PCN-PDN Information  
DOCUMENTATION  
Application Notes  
Quality And Reliability  
Symbols and Footprints  
A Low Cost Watt-Hour Energy Meter Based on the  
ADE7757  
DISCUSSIONS  
View all ADE7757 EngineerZone Discussions.  
AN-559: A Low Cost Watt-Hour Energy Meter Based on the  
ADE7755  
AN-639: Frequently Asked Questions (FAQs) Analog  
Devices Energy (ADE) Products  
SAMPLE AND BUY  
Visit the product page to see pricing options.  
Data Sheet  
ADE7757: Energy Metering IC with Integrated Oscillator  
Data Sheet  
TECHNICAL SUPPORT  
Submit a technical question or find your regional support  
number.  
REFERENCE MATERIALS  
Technical Articles  
DOCUMENT FEEDBACK  
Submit feedback for this data sheet.  
Analog Feedback - Analog/Linear IC: Filling Important  
Roles  
Digital Energy Meters by the Millions  
How Solid Is Your Solid-State Energy Meter? Not All Ics Are  
Created Equal.  
IC Technology and Failure Mechanisms - Understanding  
Reliability Standards Can Raise Quality of Meters  
Measuring Harmonic Energy with a Solid State Energy  
Meter  
Measuring Reactive Power in Energy Meters  
RF Meets Power Lines: Designing Intelligent Smart Grid  
Systems that Promote Energy Efficiency  
Solid State Solutions For Electricity Metrology  
Tapping The Potential Of Electronic Energy Metering  
Trusting Integrated Circuits in Metering Applications  
This page is dynamically generated by Analog Devices, Inc., and inserted into this data sheet. A dynamic change to the content on this page will not  
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(VDD = 5 V 5%, AGND = DGND = 0 V, On-Chip Reference, RCLKIN = 6.2 k,  
ADE7757–SPECIFICATIONS 0.5% 50 ppm/C, TMIN to TMAX = –40C to +85C, unless otherwise noted.)  
Parameter  
Value  
Unit  
Test Conditions/Comments  
ACCURACY1, 2  
Measurement Error1 on Channel V1  
Channel V2 with Full-Scale Signal ( 165 mV), 25°C  
Over a Dynamic Range 500 to 1  
Line Frequency = 45 Hz to 65 Hz  
0.1  
% Reading typ  
Phase Error1 between Channels  
V1 Phase Lead 37°  
(PF = 0.8 Capacitive)  
0.1  
0.1  
Degrees (°) max  
Degrees (°) max  
% Reading typ  
V1 Phase Lag 60°  
(PF = 0.5 Inductive)  
AC Power Supply Rejection1  
Output Frequency Variation (CF)  
S0 = S1 = 1,  
0.2  
V1 = 21.2 mV rms, V2 = 116.7 mV rms @ 50 Hz  
Ripple on VDD of 200 mV rms @ 100 Hz  
S0 = S1 = 1,  
DC Power Supply Rejection1  
Output Frequency Variation (CF)  
0.3  
% Reading typ  
V1 = 21.2 mV rms, V2 = 116.7 mV rms,  
VDD = 5 V 250 mV  
ANALOG INPUTS  
See Analog Inputs section  
V1P and V1N to AGND  
V2P and V2N to AGND  
Channel V1 Maximum Signal Level  
Channel V2 Maximum Signal Level  
Input Impedance (DC)  
Bandwidth (–3 dB)  
30  
165  
320  
7
18  
4
mV max  
mV max  
kmin  
kHz nominal  
mV max  
OSC = 450 kHz, RCLKIN = 6.2 k, 0.5%  
50 ppm/°C  
OSC = 450 kHz, RCLKIN = 6.2 k, 0.5% 50 ppm/°C  
See Terminology Section and Typical Performance Characteristics  
External 2.5 V Reference  
ADC Offset Error1, 2  
Gain Error1  
% Ideal typ  
V1 = 21.2 mV rms, V2 = 116.7 mV rms  
OSCILLATOR FREQUENCY (OSC)  
Oscillator Frequency Tolerance1  
Oscillator Frequency Stability1  
450  
12  
30  
kHz nominal  
% Reading typ  
ppm/°C typ  
RCLKIN = 6.2 k, 0.5% 50 ppm/°C  
REFERENCE INPUT  
REFIN/OUT Input Voltage Range  
2.7  
2.3  
10  
V max  
V min  
pF max  
2.5 V + 8%  
2.5 V – 8%  
Input Capacitance  
ON-CHIP REFERENCE  
Reference Error  
Temperature Coefficient  
Nominal 2.5 V  
200  
20  
mV max  
ppm/°C typ  
LOGIC INPUTS3  
SCF, S0, S1,  
Input High Voltage, VINH  
Input Low Voltage, VINL  
Input Current, IIN  
2.4  
0.8  
1
V min  
VDD = 5 V 5%  
VDD = 5 V 5%  
Typically 10 nA, VIN = 0 V to VDD  
V max  
µA max  
pF max  
Input Capacitance, CIN  
10  
LOGIC OUTPUTS3  
F1 and F2  
Output High Voltage, VOH  
ISOURCE = 10 mA  
VDD = 5 V  
ISINK = 10 mA  
4.5  
0.5  
V min  
V max  
Output Low Voltage, VOL  
V
DD = 5 V  
CF  
Output High Voltage, VOH  
ISOURCE = 5 mA  
DD = 5 V  
ISINK = 5 mA  
VDD = 5 V  
4
V min  
V
Output Low Voltage, VOL  
0.5  
10  
V max  
% Ideal typ  
Frequency Output Error1, 2 (CF)  
External 2.5 V Reference,  
V1 = 21.2 mV rms, V2 = 116.7 mV rms  
POWER SUPPLY  
VDD  
For Specified Performance  
5 V – 5%  
5 V + 5%  
4.75  
5.25  
5
V min  
V max  
mA max  
IDD  
Typically 4 mA  
NOTES  
1See Terminology section for explanation of specifications.  
2See plots in Typical Performance Characteristics.  
3Sample tested during initial release and after any redesign or process change that may affect this parameter.  
Specifications subject to change without notice.  
–2–  
REV. A  
ADE7757  
(VDD = 5 V 5%, AGND = DGND = 0 V, On-Chip Reference, RCLKIN = 6.2 k,  
TIMING CHARACTERISTICS1, 2 0.5% 50 ppm/C, TMIN to TMAX = –40C to +85C, unless otherwise noted.)  
Parameter  
A, B Versions  
Unit  
Test Conditions/Comments  
3
t1  
t2  
244  
See Table II  
1/2 t2  
173  
See Table III  
2
ms  
sec  
sec  
ms  
sec  
µs  
F1 and F2 Pulse Width (Logic Low).  
Output Pulse Period. See Transfer Function section.  
Time between F1 Falling Edge and F2 Falling Edge.  
CF Pulse Width (Logic High).  
CF Pulse Period. See Transfer Function section.  
Minimum Time between F1 and F2 Pulses.  
t33, 4  
t4  
t5  
t6  
NOTES  
1Sample tested during initial release and after any redesign or process change that may affect this parameter.  
2See Figure 1.  
3The pulse widths of F1, F2, and CF are not fixed for higher output frequencies. See Frequency Outputs section.  
4The CF pulse is always 35 µs in the high frequency mode. See Frequency Outputs section and Table III.  
Specifications subject to change without notice.  
t1  
F1  
t6  
t2  
F2  
t3  
t4  
t5  
CF  
Figure 1. Timing Diagram for Frequency Outputs  
REV. A  
–3–  
ADE7757  
ABSOLUTE MAXIMUM RATINGS1  
Power Supply Rejection  
(TA = 25°C, unless otherwise noted.)  
This quantifies the ADE7757 measurement error as a percent-  
age of reading when the power supplies are varied.  
VDD to AGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V  
VDD to DGND . . . . . . . . . . . . . . . . . . . . . . . . . –0.3 V to +7 V  
Analog Input Voltage to AGND  
V1P, V1N, V2P, and V2N . . . . . . . . . . . . . . . . –6 V to +6 V  
Reference Input Voltage to AGND . . . –0.3 V to VDD + 0.3 V  
Digital Input Voltage to DGND . . . . . –0.3 V to VDD + 0.3 V  
Digital Output Voltage to DGND . . . . –0.3 V to VDD + 0.3 V  
Operating Temperature Range  
For the ac PSR measurement, a reading at nominal supplies  
(5 V) is taken. A 200 mV rms/100 Hz signal is then introduced  
onto the supplies and a second reading is obtained under the  
same input signal levels. Any error introduced is expressed as a  
percentage of reading—see the Measurement Error definition.  
For the dc PSR measurement, a reading at nominal supplies  
(5 V) is taken. The supplies are then varied 5% and a second  
reading is obtained with the same input signal levels. Any error  
introduced is again expressed as a percentage of reading.  
Industrial (A, B Versions) . . . . . . . . . . . . . –40°C to +85°C  
Storage Temperature Range . . . . . . . . . . . . –65°C to +150°C  
Junction Temperature . . . . . . . . . . . . . . . . . . . . . . . . . . 150°C  
16-Lead Plastic SOIC, Power Dissipation . . . . . . . . . 350 mW  
ADC Offset Error  
JA Thermal Impedance2 . . . . . . . . . . . . . . . . . . .124.9°C/W  
This refers to the small dc signal (offset) associated with the  
analog inputs to the ADCs. However, the HPF in Channel V1  
eliminates the offset in the circuitry. Therefore, the power cal-  
culation is not affected by this offset.  
Lead Temperature, Soldering  
Vapor Phase (60 sec) . . . . . . . . . . . . . . . . . . . . . . . . . 215°C  
Infrared (15 sec) . . . . . . . . . . . . . . . . . . . . . . . . . . . . 220°C  
NOTES  
Frequency Output Error (CF)  
1 Stresses above those listed under Absolute Maximum Ratings may cause perma-  
nent damage to the device. This is a stress rating only; functional operation of the  
device at these or any other conditions above those listed in the operational  
sections of this specification is not implied. Exposure to absolute maximum rating  
conditions for extended periods may affect device reliability.  
2 JEDEC 1S Standard (2-layer) Board Data.  
The frequency output error of the ADE7757 is defined as the  
difference between the measured output frequency (minus  
the offset) and the ideal output frequency. The difference is  
expressed as a percentage of the ideal frequency. The ideal  
frequency is obtained from the ADE7757 transfer function  
(see the Transfer Function section).  
ORDERING GUIDE  
Gain Error  
The gain error of the ADE7757 is defined as the difference  
between the measured output frequency (minus the offset) and  
the ideal output frequency. The difference is expressed as a  
percentage of the ideal frequency. The ideal frequency is obtained  
from the ADE7757 transfer function (see the Transfer Function  
section).  
Model  
Package Description Package Options  
ADE7757ARN  
ADE7757ARNRL  
SOIC Narrow-Body  
SOIC Narrow-Body  
in Reel  
RN-16  
RN-16  
EVAL-ADE7757EB Evaluation Board  
ADE7757ARN-REF Reference Design  
Evaluation Board  
Reference Design  
Oscillator Frequency Tolerance  
The oscillator frequency tolerance of the ADE7757 is defined as  
part-to-part frequency variation in terms of percentage at room  
temperature (25°C). It is measured by taking the difference  
between the measured oscillator frequency and the nominal  
frequency defined in the Specifications section.  
TERMINOLOGY  
Measurement Error  
The error associated with the energy measurement made by the  
ADE7757 is defined by the following formula  
Oscillator Frequency Stability  
Energy Registered by ADE7757–True Energy  
%Error =  
¥ 100%  
Oscillator frequency stability is defined as frequency variation  
in terms of parts-per-million drift over the operating tem-  
perature range. In a metering application, the temperature  
range is –40°C to +85°C. Oscillator frequency stability is  
measured by taking the difference between the measured  
oscillator frequency at –40°C and +85°C and the measured  
oscillator frequency at +25°C.  
True Energy  
Phase Error between Channels  
The HPF (high-pass filter) in the current channel (Channel V1)  
has a phase lead response. To offset this phase response and  
equalize the phase response between channels, a phase correc-  
tion network is also placed in Channel V1. The phase correction  
network matches the phase to within 0.1° over a range of 45 Hz  
to 65 Hz, and 0.2° over a range 40 Hz to 1 kHz (see Figures  
11 and 12).  
CAUTION  
ESD (electrostatic discharge) sensitive device. Electrostatic charges as high as 4000 V readily  
accumulate on the human body and test equipment and can discharge without detection. Although the  
ADE7757 features proprietary ESD protection circuitry, permanent damage may occur on devices  
subjected to high energy electrostatic discharges. Therefore, proper ESD precautions are recommended  
to avoid performance degradation or loss of functionality.  
–4–  
REV. A  
ADE7757  
PIN CONFIGURATION  
V
1
2
3
4
5
6
7
8
16 F1  
15 F2  
DD  
V2P  
V2N  
14  
13  
12  
CF  
ADE7757  
DGND  
REVP  
V1N  
TOP VIEW  
V1P  
(Not to Scale)  
AGND  
11 RCLKIN  
10 S0  
REF  
IN/OUT  
SCF  
9
S1  
PIN FUNCTION DESCRIPTIONS  
Pin No.  
Mnemonic  
Description  
1
VDD  
Power Supply. This pin provides the supply voltage for the circuitry in the ADE7757. The supply voltage  
should be maintained at 5 V 5% for specified operation. This pin should be decoupled with a 10 µF  
capacitor in parallel with a ceramic 100 nF capacitor.  
2, 3  
4, 5  
6
V2P, V2N  
V1N, V1P  
AGND  
Analog Inputs for Channel V2 (voltage channel). These inputs provide a fully differential input pair. The  
maximum differential input voltage is 165 mV for specified operation. Both inputs have internal ESD  
protection circuitry; an overvoltage of 6 V can be sustained on these inputs without risk of permanent  
damage.  
Analog Inputs for Channel V1 (current channel). These inputs are fully differential voltage inputs with a  
maximum signal level of 30 mV with respect to the V1N pin for specified operation. Both inputs have  
internal ESD protection circuitry and, in addition, an overvoltage of 6 V can be sustained on these  
inputs without risk of permanent damage.  
This provides the ground reference for the analog circuitry in the ADE7757, i.e., ADCs and reference.  
This pin should be tied to the analog ground plane of the PCB. The analog ground plane is the ground  
reference for all analog circuitry, e.g., antialiasing filters, current and voltage sensors, and so forth. For  
accurate noise suppression, the analog ground plane should be connected to the digital ground plane at  
only one point. A star ground configuration will help to keep noisy digital currents away from the analog  
circuits.  
7
REFIN/OUT  
This pin provides access to the on-chip voltage reference. The on-chip reference has a nominal value  
of 2.5 V and a typical temperature coefficient of 20 ppm/°C. An external reference source may also  
be connected at this pin. In either case, this pin should be decoupled to AGND with a 1 µF tanta-  
lum capacitor and a 100 nF ceramic capacitor. The internal reference cannot be used to drive an  
external load.  
8
SCF  
Select Calibration Frequency. This logic input is used to select the frequency on the calibration output  
CF. Table III shows calibration frequencies selection.  
9, 10  
S1, S0  
These logic inputs are used to select one of four possible frequencies for the digital-to-frequency conver-  
sion. With this logic input, designers have greater flexibility when designing an energy meter. See the  
Selecting a Frequency for an Energy Meter Application section.  
11  
12  
RCLKIN  
REVP  
To enable the internal oscillator as a clock source to the chip, a precise low temperature drift resistor at a  
nominal value of 6.2 kmust be connected from this pin to DGND.  
This logic output will go high when negative power is detected, i.e., when the phase angle between the  
voltage and current signals is greater than 90°. This output is not latched and will be reset when positive  
power is once again detected. The output will go high or low at the same time that a pulse is issued on CF.  
13  
DGND  
This provides the ground reference for the digital circuitry in the ADE7757, i.e., multiplier, filters, and  
digital-to-frequency converter. This pin should be tied to the digital ground plane of the PCB. The digi-  
tal ground plane is the ground reference for all digital circuitry, e.g., counters (mechanical and digital),  
MCUs, and indicator LEDs. For accurate noise suppression, the analog ground plane should be con-  
nected to the digital ground plane at one point only, i.e., a star ground.  
14  
CF  
Calibration Frequency Logic Output. The CF logic output provides instantaneous real power informa-  
tion. This output is intended for calibration purposes. Also see SCF pin description.  
15, 16  
F2, F1  
Low Frequency Logic Outputs. F1 and F2 supply average real power information. The logic outputs can  
be used to directly drive electromechanical counters and 2-phase stepper motors. See the Transfer Func-  
tion section.  
REV. A  
–5–  
ADE7757–Typical Performance Characteristics  
V
DD  
100nF  
10F  
K7  
K8  
V
DD  
U3  
602kꢁ  
200ꢁ  
F1  
V2P  
F2  
150nF  
220V  
U1  
CF  
ADE7757  
200ꢁ  
V2N  
40A TO  
40mA  
PS2501-1  
150nF  
REVP  
200ꢁ  
6.2kꢁ  
V1P  
V1N  
RCLKIN  
150nF  
V
DD  
350ꢆꢁ  
200ꢁ  
10kꢁ  
150nF  
100nF  
S0  
S1  
REF  
IN/OUT  
SCF  
1F  
10nF  
10nF  
10nF  
AGND DGND  
Figure 2. Test Circuit for Performance Curves  
0.5  
0.4  
1.0  
PF = 1  
ON-CHIP REFERENCE  
PF = 1  
EXTERNAL REFERENCE  
0.8  
0.6  
0.3  
+85C  
0.2  
0.4  
+85C  
–40C  
+25C  
+25C  
0.1  
0.2  
0
0
–0.1  
–0.2  
–0.3  
–0.4  
–0.5  
–0.2  
–0.4  
–0.6  
–0.8  
–1.0  
–40C  
0.01  
0.1  
1
10  
100  
0.01  
0.1  
1
10  
100  
CURRENT – A  
CURRENT – A  
TPC 1. Error as a % of Reading over Temperature  
with On-Chip Reference (PF = 1)  
TPC 3. Error as a % of Reading over Temperature  
with External Reference (PF = 1)  
1.0  
0.9  
PF = 0.5  
ON-CHIP REFERENCE  
PF = 0.5  
EXTERNAL REFERENCE  
0.8  
0.7  
–40C, PF = 0.5  
0.6  
0.5  
0.4  
+85C, PF = 0.5  
+85C, PF = 0.5  
0.2  
0
0.3  
+25C, PF = 1.0  
+25C, PF = 0.5  
–40C, PF = 0.5  
0.1  
–0.2  
–0.4  
–0.6  
–0.8  
–1.0  
+25C, PF = 1.0  
–0.1  
–25C, PF = 0.5  
–0.3  
–0.5  
0.01  
0.01  
0.1  
1
10  
100  
0.1  
1
10  
100  
CURRENT – A  
CURRENT – A  
TPC 4. Error as a % of Reading over Temperature  
with External Reference (PF = 0.5)  
TPC 2. Error as a % of Reading over Temperature  
with On-Chip Reference (PF = 0.5)  
–6–  
REV. A  
ADE7757  
0.5  
0.4  
45  
40  
35  
30  
25  
20  
15  
10  
0.5  
0
DISTRIBUTION CHARACTERISTICS  
NUMBER POINTS: 100  
INTERNAL REFERENCE  
TEMPERATURE = 25C  
PF = +0.5  
MINIMUM: –4.319mV  
0.3  
MAXIMUM: 2.2828mV  
MEAN: –1.04576552mV  
STD. DEV: 1.300956604mV  
PF = –0.5  
0.2  
0.1  
0
PF = +1.0  
–0.1  
–0.2  
–0.3  
–0.4  
–0.5  
45  
50  
55  
FREQUENCY – Hz  
60  
65  
–8 –7 –6 –5 –4 –3 –2 –1  
0
1
2
3
4
5
6
7
8
mV  
TPC 5. Error as a % of Reading over Input Frequency  
TPC 8. Channel V1 Offset Distribution  
1.0  
45  
40  
35  
30  
25  
20  
15  
10  
0.5  
0
PF = 1  
DISTRIBUTION CHARACTERISTICS  
NUMBER POINTS: 100  
ON-CHIP REFERENCE  
0.8  
MINIMUM: –9.82923mV  
MAXIMUM: 0.472126mV  
MEAN: 4.54036589mV  
STD. DEV: 1.89694475mV  
INTERNAL REFERENCE  
0.6  
TEMPERATURE = 25C  
5.25V  
0.4  
0.2  
5.0V  
0
–0.2  
4.75V  
–0.4  
–0.6  
–0.8  
–1.0  
0.01  
0.1  
1
10  
100  
–20 –18 –16 –14 –12 –10 –8 –6 –4 –2  
mV  
0
2
4
6
8
10  
CURRENT – A  
TPC 9. Channel V2 Offset Distribution  
TPC 6. PSR with Internal Reference  
1.0  
40  
35  
30  
25  
20  
15  
10  
0.5  
0
PF = 1  
DISTRIBUTION CHARACTERISTICS  
NUMBER POINTS: 100  
EXTERNAL REFERENCE  
0.8  
0.6  
EXTERNAL REFERENCE  
MINIMUM: –6.15%  
MAXIMUM: 9.96%  
MEAN: 0%  
TEMPERATURE = 25C  
5.25V  
5.0V  
0.4  
STD. DEV: 2.84%  
0.2  
0
–0.2  
–0.4  
–0.6  
–0.8  
–1.0  
4.75V  
0.01  
0.1  
1
10  
100  
CURRENT – A  
%
TPC 7. PSR with External Reference  
TPC 10. Part-to-Part CF Distribution from Mean  
REV. A  
–7–  
ADE7757  
THEORY OF OPERATION  
The low frequency outputs (F1, F2) of the ADE7757 are gener-  
ated by accumulating this real power information. This low  
frequency inherently means a long accumulation time between  
output pulses. Consequently, the resulting output frequency is  
proportional to the average real power. This average real power  
information is then accumulated (e.g., by a counter) to generate  
real energy information. Conversely, due to its high output  
frequency and hence shorter integration time, the CF output  
frequency is proportional to the instantaneous real power. This  
is useful for system calibration, which can be done faster under  
steady load conditions.  
The two ADCs digitize the voltage signals from the current  
and voltage sensors. These ADCs are 16-bit -with an  
oversampling rate of 450 kHz. This analog input structure  
greatly simplifies sensor interfacing by providing a wide dynamic  
range for direct connection to the sensor and also simplifies the  
antialiasing filter design. A high-pass filter in the current chan-  
nel removes any dc component from the current signal. This  
eliminates any inaccuracies in the real power calculation due to  
offsets in the voltage or current signals. Because the HPF is  
always enabled, the IC will operate only with ac input (see HPF  
and Offset Effects section).  
Power Factor Considerations  
The real power calculation is derived from the instantaneous  
power signal. The instantaneous power signal is generated by a  
direct multiplication of the current and voltage signals. In order  
to extract the real power component (i.e., the dc component),  
the instantaneous power signal is low-pass filtered. Figure 3  
illustrates the instantaneous real power signal and shows how  
the real power information can be extracted by low-pass filtering  
the instantaneous power signal. This scheme correctly calculates  
real power for sinusoidal current and voltage waveforms at all  
power factors. All signal processing is carried out in the digital  
domain for superior stability over temperature and time.  
The method used to extract the real power information from the  
instantaneous power signal (i.e., by low-pass filtering) is still  
valid even when the voltage and current signals are not in phase.  
Figure 4 displays the unity power factor condition and a DPF  
(displacement power factor) = 0.5, i.e., current signal lagging the  
voltage by 60°. If we assume the voltage and current waveforms  
are sinusoidal, the real power component of the instantaneous  
power signal (i.e., the dc term) is given by  
V × 1  
× cos 60°  
(
)
2   
This is the correct real power calculation.  
DIGITAL-TO-  
FREQUENCY  
HPF  
F1  
INSTANTANEOUS  
POWER SIGNAL  
INSTANTANEOUS REAL  
POWER SIGNAL  
CH1  
CH2  
ADC  
F2  
LPF  
POWER  
MULTIPLIER  
DIGITAL-TO-  
FREQUENCY  
ADC  
CF  
V I  
2
INSTANTANEOUS  
POWER SIGNAL – p(t)  
INSTANTANEOUS REAL  
POWER SIGNAL  
0V  
TIME  
CURRENT  
VOLTAGE  
INSTANTANEOUS REAL  
POWER SIGNAL  
POWER  
INSTANTANEOUS  
POWER SIGNAL  
TIME  
TIME  
Figure 3. Signal Processing Block Diagram  
V I  
2
COS (60)  
0V  
TIME  
VOLTAGE  
CURRENT  
60ꢀ  
Figure 4. DC Component of Instantaneous Power  
Signal Conveys Real Power Information, PF < 1  
–8–  
REV. A  
ADE7757  
ANALOG INPUTS  
Nonsinusoidal Voltage and Current  
Channel V1 (Current Channel)  
The real power calculation method also holds true for  
nonsinusoidal current and voltage waveforms. All voltage and  
current waveforms in practical applications will have some har-  
monic content. Using the Fourier Transform, instantaneous  
voltage and current waveforms can be expressed in terms of  
their harmonic content.  
The voltage output from the current sensor is connected to the  
ADE7757 here. Channel V1 is a fully differential voltage input.  
V1P is the positive input with respect to V1N.  
The maximum peak differential signal on Channel V1 should be  
less than 30 mV (21 mV rms for a pure sinusoidal signal) for  
specified operation.  
v t =V + 2 × Σ V × sin hωt +α  
( )  
(1)  
(
)
h
h
0
ho  
V1  
where:  
+30mV  
V1P  
V1N  
v(t) is the instantaneous voltage.  
V0 is the average value.  
Vh is the rms value of voltage harmonic h.  
DIFFERENTIAL INPUT  
+
V1  
V
؎30mV MAX PEAK  
V
CM  
COMMON-MODE  
؎6.25mV MAX  
+
h is the phase angle of the voltage harmonic.  
CM  
AGND  
i t = I + 2 × Σ I × sin hωt + β  
–30mV  
( )  
(2)  
(
)
h
h
0
ho  
where:  
Figure 5. Maximum Signal Levels, Channel V1  
i(t) is the instantaneous current.  
I0 is the dc component.  
Ih is the rms value of current harmonic h.  
h is the phase angle of the current harmonic.  
The diagram in Figure 5 illustrates the maximum signal levels  
on V1P and V1N. The maximum differential voltage is 30 mV.  
The differential voltage signal on the inputs must be referenced  
to a common mode, e.g., AGND. The maximum common-  
mode signal is 6.25 mV, as shown in Figure 5.  
Using Equations 1 and 2, the real power P can be expressed in  
terms of its fundamental real power (P1) and harmonic real  
power (PH).  
Channel V2 (Voltage Channel)  
The output of the line voltage sensor is connected to the  
ADE7757 at this analog input. Channel V2 is a fully differen-  
tial voltage input with a maximum peak differential signal of  
165 mV. Figure 6 illustrates the maximum signal levels that  
can be connected to the ADE7757 Channel V2.  
P = P + PH  
1
where  
P =V1 × I1 cosφ1  
1
(3)  
φ1 = α1 β1  
V2  
and  
+165mV  
V2P  
V2N  
DIFFERENTIAL INPUT  
+
PH = ∑Vh × Ih cosφh  
V2  
V
؎165mV MAX PEAK  
h1  
V
(4)  
CM  
COMMON-MODE  
+
φh = αh βh  
CM  
؎25mV MAX  
As can be seen from Equation 4, a harmonic real power compo-  
nent is generated for every harmonic, provided that harmonic is  
present in both the voltage and current waveforms. The power  
factor calculation has previously been shown to be accurate in  
the case of a pure sinusoid. Therefore, the harmonic real power  
must also correctly account for power factor since it is made up  
of a series of pure sinusoids.  
AGND  
–165mV  
Figure 6. Maximum Signal Levels, Channel V2  
Channel V2 is usually driven from a common-mode voltage,  
i.e., the differential voltage signal on the input is referenced to a  
common mode (usually AGND). The analog inputs of the  
ADE7757 can be driven with common-mode voltages of up to  
25 mV with respect to AGND. However, best results are achieved  
using a common mode equal to AGND.  
Note that the input bandwidth of the analog inputs is 7 kHz at  
the nominal internal oscillator frequency of 450 kHz.  
REV. A  
–9–  
ADE7757  
Typical Connection Diagrams  
V
DD  
Figure 7 shows a typical connection diagram for Channel V1. A  
shunt is the current sensor selected for this example because of  
its low cost compared to other current sensors such as the CT  
(current transformer). This IC is ideal for low current meters.  
5V  
4V  
R
V1P  
V1N  
F
0V  
C
F
TIME  
SHUNT  
AGND  
30mV  
C
R
F
F
INTERNAL  
ACTIVATION  
INACTIVE  
ACTIVE  
INACTIVE  
PHASE NEUTRAL  
Figure 7. Typical Connection for Channel V1  
Figure 9. On-Chip Power Supply Monitor  
HPF and Offset Effects  
Figure 8 shows a typical connection for Channel V2. Typically,  
the ADE7757 is biased around the phase wire, and a resistor  
divider is used to provide a voltage signal that is proportional to  
the line voltage. Adjusting the ratio of RA, RB, and RF is also a  
convenient way of carrying out a gain calibration on a meter.  
Figure 10 illustrates the effect of offsets on the real power calcu-  
lation. As can be seen, offsets on Channel V1 and Channel V2  
will contribute a dc component after multiplication. Since this  
dc component is extracted by the LPF and used to generate the  
real power information, the offsets will contribute a constant  
error to the real power calculation. This problem is easily avoided  
by the built-in HPF in Channel V1. By removing the offsets  
from at least one channel, no error component can be generated  
at dc by the multiplication. Error terms at the line frequency ()  
are removed by the LPF and the digital-to-frequency conversion  
(see Digital-to-Frequency Conversion section).  
R
B
R
*
V2P  
V2N  
A
165mV  
R
C
F
F
R
C
F
F
*R >> R + R  
F
NEUTRAL PHASE  
A
B
The equation below shows how the power calculation is affected  
by the dc offsets in the current and voltage channels.  
Figure 8. Typical Connections for Channel V2  
V cos ωt +V  
× I cos ωt + I  
(
)
(
)
{
}
{
}
)
POWER SUPPLY MONITOR  
OS  
OS  
The ADE7757 contains an on-chip power supply monitor. The  
power supply (VDD) is continuously monitored by the ADE7757.  
If the supply is less than 4 V, the ADE7757 becomes inactive.  
This is useful to ensure proper device operation at power-up  
and power-down. The power supply monitor has built in hyster-  
esis and filtering that provide a high degree of immunity to false  
triggering from noisy supplies.  
V × I  
2
=
+VOS × IOS +VOS × I cos ωt + I ×V cos ωt  
(
(
)
OS  
V × I  
2
+
× cos 2ωt  
(
)
DC COMPONENT (INCLUDING ERROR TERM)  
IS EXTRACTED BY THE LPF FOR REAL  
POWER CALCULATION  
As can be seen from Figure 9, the trigger level is nominally set  
at 4 V. The tolerance on this trigger level is within 5%. The  
power supply and decoupling for the part should be such that  
the ripple at VDD does not exceed 5 V 5% as specified for  
normal operation.  
V
I  
OS  
OS  
V I  
2
I
V  
I  
OS  
V
OS  
0
FREQUENCY – RAD/s  
Figure 10. Effect of Channel Offset on the Real  
Power Calculation  
–10–  
REV. A  
ADE7757  
For a line frequency of 50 Hz, this would give an attenuation  
of the 2(100 Hz) component of approximately 22 dB. The  
dominating harmonic will be at twice the line frequency (2)  
due to the instantaneous power calculation.  
The HPF in Channel V1 has an associated phase response that  
is compensated for on-chip. Figures 11 and 12 show the phase  
error between channels with the compensation network acti-  
vated. The ADE7757 is phase compensated up to 1 kHz as  
shown. This will ensure correct active harmonic power calcula-  
tion even at low power factors.  
Figure 13 shows the instantaneous real power signal at the output  
of the LPF that still contains a significant amount of instanta-  
neous power information, i.e., cos(2t). This signal is then passed  
to the digital-to-frequency converter where it is integrated  
(accumulated) over time in order to produce an output frequency.  
The accumulation of the signal will suppress or average out any  
non-dc components in the instantaneous real power signal. The  
average value of a sinusoidal signal is zero. Thus, the frequency  
generated by the ADE7757 is proportional to the average real  
power. Figure 13 shows the digital-to-frequency conversion for  
steady load conditions, i.e., constant voltage and current.  
0.30  
0.25  
0.20  
0.15  
0.10  
0.05  
0
F1  
DIGITAL-TO-  
FREQUENCY  
–0.05  
–0.10  
F1  
V
F2  
LPF  
TIME  
TIME  
0
100 200 300 400 500 600 700 800 900 1000  
FREQUENCY – Hz  
MULTIPLIER  
I
DIGITAL-TO-  
FREQUENCY  
CF  
Figure 11. Phase Error between Channels (0 Hz to 1 kHz)  
CF  
LPF TO EXTRACT  
REAL POWER  
(DC TERM)  
0.30  
0.25  
0.20  
0.15  
0.10  
0.05  
0
VI  
2
COS (2)  
ATTENUATED BY LPF  
0
2ꢈ  
FREQUENCY (RAD/s)  
INSTANTANEOUS REAL POWER SIGNAL  
(FREQUENCY DOMAIN)  
Figure 13. Real Power-to-Frequency Conversion  
As can be seen in the diagram, the frequency output CF is seen  
to vary over time, even under steady load conditions. This fre-  
quency variation is primarily due to the cos(2t) component in  
the instantaneous real power signal. The output frequency on  
CF can be up to 2048 times higher than the frequency on F1  
and F2. This higher output frequency is generated by accumu-  
lating the instantaneous real power signal over a much shorter  
time while converting it to a frequency. This shorter accumula-  
tion period means less averaging of the cos(2t) component.  
Consequently, some of this instantaneous power signal passes  
through the digital-to-frequency conversion. This will not be a  
problem in the application. Where CF is used for calibration  
purposes, the frequency should be averaged by the frequency  
counter, which will remove any ripple. If CF is being used to  
measure energy, for example in a microprocessor based applica-  
tion, the CF output should also be averaged to calculate power.  
–0.05  
–0.10  
40  
45  
50  
55  
60  
65  
70  
FREQUENCY – Hz  
Figure 12. Phase Error between Channels (40 Hz to 70 Hz)  
Digital-to-Frequency Conversion  
As previously described, the digital output of the low-pass filter  
after multiplication contains the real power information. However,  
since this LPF is not an ideal “brick wall” filter implementation,  
the output signal also contains attenuated components at the  
line frequency and its harmonics, i.e., cos(ht) where h = 1, 2,  
3, . . . and so on.  
The magnitude response of the filter is given by  
1
|H f |=  
( )  
f 2  
Because the outputs F1 and F2 operate at a much lower fre-  
quency, a lot more averaging of the instantaneous real power  
signal is carried out. The result is a greatly attenuated sinusoidal  
content and a virtually ripple-free frequency output.  
(5)  
1+  
4.452  
REV. A  
–11–  
ADE7757  
Interfacing the ADE7757 to a Microcontroller for Energy  
Measurement  
INTERNAL OSCILLATOR (OSC)  
The nominal internal oscillator frequency is 450 kHz when used  
with RCLKIN with a nominal value of 6.2 k. The frequency  
outputs are directly proportional to the oscillator frequency,  
thus RCLKIN must have low tolerance and low temperature  
drift to ensure stability and linearity of the chip. The oscillator  
frequency is inversely proportional to the RCLKIN as shown in  
Figure 15. Although the internal oscillator operates when used  
with RCLKIN values between 5.5 kand 20 k, choosing a  
value within the range of the nominal value, as shown in Figure 15,  
is recommended.  
The easiest way to interface the ADE7757 to a microcontroller  
is to use the CF high frequency output with the output frequency  
scaling set to 2048 × F1, F2. This is done by setting SCF = 0  
and S0 = S1 = 1 (see Table III). With full-scale ac signals on  
the analog inputs, the output frequency on CF will be approxi-  
mately 2.867 kHz. Figure 14 illustrates one scheme that could  
be used to digitize the output frequency and carry out the neces-  
sary averaging mentioned in the previous section.  
CF  
FREQUENCY  
RIPPLE  
490  
480  
470  
460  
450  
440  
430  
420  
410  
400  
AVERAGE  
FREQUENCY  
10%  
TIME  
MCU  
ADE7757  
COUNTER  
CF  
TIMER  
5.8  
5.9  
6.0  
6.1  
6.2  
6.3  
6.4  
6.5  
6.6  
6.7  
RESISTANCE – kꢁ  
Figure 14. Interfacing the ADE7757 to an MCU  
Figure 15. Effect of RCLKIN on Internal Oscillator  
Frequency (OSC)  
As shown, the frequency output CF is connected to an MCU  
counter or port. This will count the number of pulses in a given  
integration time, which is determined by an MCU internal timer.  
The average power proportional to the average frequency is  
given by  
TRANSFER FUNCTION  
Frequency Outputs F1 and F2  
The ADE7757 calculates the product of two voltage signals (on  
Channel V1 and Channel V2) and then low-pass filters this  
product to extract real power information. This real power  
information is then converted to a frequency. The frequency  
information is output on F1 and F2 in the form of active low  
pulses. The pulse rate at these outputs is relatively low, e.g.,  
0.175 Hz maximum for ac signals with S0 = S1 = 0 (see Table II).  
This means that the frequency at these outputs is generated  
from real power information accumulated over a relatively long  
period of time. The result is an output frequency that is propor-  
tional to the average real power. The averaging of the real power  
signal is implicit to the digital-to-frequency conversion. The  
output frequency or pulse rate is related to the input voltage  
signals by the following equation  
Counter  
Average Frequency = Average Power =  
Time  
The energy consumed during an integration period is given by  
Counter  
Time  
Energy = Average Power × Time =  
× Time = Counter  
For the purpose of calibration, this integration time could be  
10 seconds to 20 seconds in order to accumulate enough pulses to  
ensure correct averaging of the frequency. In normal opera-  
tion, the integration time could be reduced to one or two seconds,  
depending, for example, on the required update rate of a dis-  
play. With shorter integration times on the MCU, the amount  
of energy in each update may still have some small amount of  
ripple, even under steady load conditions. However, over a  
minute or more the measured energy will have no ripple.  
515.84 ×V1 ×V2rms × F14  
rms  
Freq =  
2
VREF  
Power Measurement Considerations  
where  
Calculating and displaying power information will always have  
some associated ripple that will depend on the integration period  
used in the MCU to determine average power and also on the  
load. For example, at light loads, the output frequency may be  
10 Hz. With an integration period of two seconds, only about  
20 pulses will be counted. The possibility of missing one pulse  
always exists as the ADE7757 output frequency is running  
asynchronously to the MCU timer. This would result in a one-  
in-twenty or 5% error in the power measurement.  
Freq = Output frequency on F1 and F2 (Hz).  
V1rms = Differential rms voltage signal on Channel V1 (V).  
V2rms = Differential rms voltage signal on Channel V2 (V).  
VREF = The reference voltage (2.5 V 8%) (V).  
F1-4 = One of four possible frequencies selected by using the  
logic inputs S0 and S1—see Table I.  
–12–  
REV. A  
ADE7757  
Table I. F1–4 Frequency Selection  
Table III. Maximum Output Frequency on CF  
F1–4 at Nominal  
SCF  
S1  
S0  
CF Max for AC Signals (Hz)*  
S1  
S0  
OSC Relation1  
OSC (Hz)2  
1
0
1
0
1
0
1
0
0
0
0
0
1
1
1
1
0
0
1
1
0
0
1
1
128 × F1, F2 = 22.4  
64 × F1, F2 = 11.2  
64 × F1, F2 = 22.4  
32 × F1, F2 = 11.2  
32 × F1, F2 = 22.4  
16 × F1, F2 = 11.2  
16 × F1, F2 = 22.4  
2048 × F1, F2 = 2.867 kHz  
0
0
1
1
0
1
0
1
OSC/219  
OSC/218  
OSC/217  
OSC/216  
0.86  
1.72  
3.44  
6.86  
NOTES  
1F1–4 is a binary fraction of the internal oscillator frequency (OSC).  
2Values are generated using the nominal frequency of 450 kHz.  
Example  
*Values are generated using the nominal frequency of 450 kHz.  
In this example, with ac voltages of 30 mV peak applied to V1  
and 165 mV peak applied to V2, the expected output frequency  
is calculated as follows:  
SELECTING A FREQUENCY FOR AN ENERGY METER  
APPLICATION  
F1–4 = OSC/219 Hz, S0 = S1 = 0  
V1rms = 0.03/2 V  
As shown in Table I, the user can select one of four frequencies.  
This frequency selection determines the maximum frequency on  
F1 and F2. These outputs are intended for driving an energy  
register (electromechanical or others). Since only four different  
output frequencies can be selected, the available frequency  
selection has been optimized for a meter constant of 100 imp/kWh  
with a maximum current of between 10 A and 120 A. Table IV  
V2rms = 0.165/2 V  
VREF = 2.5 V (nominal reference value)  
NOTE: If the on-chip reference is used, actual output frequencies may vary  
from device to device due to reference tolerance of 8%.  
515.85 × 0.03 × 0.165 × F1  
shows the output frequency for several maximum currents (IMAX  
)
Freq =  
= 0.204 × F1 = 0.175  
2 × 2 × 2.52  
with a line voltage of 220 V. In all cases, the meter constant is  
100 imp/kWh.  
Table II. Maximum Output Frequency on F1 and F2  
Table IV. F1 and F2 Frequency at 100 imp/kWh  
Max Frequency*  
for AC Inputs (Hz)  
IMAX (A)  
F1 and F2 (Hz)  
S1  
S0  
OSC Relation  
12.5  
25.0  
40.0  
60.0  
80.0  
120.0  
0.076  
0.153  
0.244  
0.367  
0.489  
0.733  
0
0
1
1
0
1
0
1
0.204 × F1  
0.204 × F2  
0.204 × F3  
0.204 × F4  
0.175  
0.35  
0.70  
1.40  
*Values are generated using the nominal frequency of 450 kHz  
Frequency Output CF  
The F1–4 frequencies allow complete coverage of this range of  
output frequencies (F1, F2). When designing an energy meter,  
the nominal design voltage on Channel V2 (voltage) should be  
set to half-scale to allow for calibration of the meter constant.  
The current channel should also be no more than half-scale  
when the meter sees maximum load. This will allow overcurrent  
signals and signals with high crest factors to be accommodated.  
Table V shows the output frequency on F1 and F2 when both  
analog inputs are half-scale. The frequencies listed in Table V  
align very well with those listed in Table IV for maximum load.  
The pulse output CF (calibration frequency) is intended for  
calibration purposes. The output pulse rate on CF can be up to  
2048 times the pulse rate on F1 and F2. The lower the F1–4  
frequency selected, the higher the CF scaling (except for the  
high frequency mode SCF = 0, S1 = S0 = 1). Table III shows  
how the two frequencies are related, depending on the states of  
the logic inputs S0, S1, and SCF. Due to its relatively high  
pulse rate, the frequency at CF logic output is proportional to  
the instantaneous real power. As with F1 and F2, CF is derived  
from the output of the low-pass filter after multiplication. How-  
ever, because the output frequency is high, this real power  
information is accumulated over a much shorter time. There-  
fore, less averaging is carried out in the digital-to-frequency  
conversion. With much less averaging of the real power signal,  
the CF output is much more responsive to power fluctuations  
(see the Signal Processing Block in Figure 3).  
REV. A  
–13–  
ADE7757  
Table V. F1 and F2 Frequency with Half-Scale AC Inputs  
CF pulse width is set to half the period. For example, if the CF  
frequency is 20 Hz, the CF pulse width is 25 ms.  
Frequency on F1 and F2–  
S1 S0 F1–4 (Hz)* CH1 and CH2 Half-Scale AC Input*  
NOTE: When the high frequency mode is selected (i.e., SCF =  
0, S1 = S0 = 1), the CF pulse width is fixed at 35 µs. Therefore,  
t4 will always be 35 µs, regardless of output frequency on CF.  
0
0
1
1
0
1
0
1
0.86  
1.72  
3.44  
6.86  
0.051 × F1 0.044 Hz  
0.051 × F2 0.088 Hz  
0.051 × F3 0.176 Hz  
0.051 × F4 0.352 Hz  
NO LOAD THRESHOLD  
The ADE7757 also includes a no-load threshold and start-up  
current feature that will eliminate any creep effects in the meter.  
The ADE7757 is designed to issue a minimum output frequency.  
Any load generating a frequency lower than this minimum fre-  
quency will not cause a pulse to be issued on F1, F2, or CF.  
The minimum output frequency is given as 0.0014% for each of  
the F1–4 frequency selections (see Table I). For example, for an  
energy meter with a meter constant of 100 imp/kWh on F1, F2  
using F3 (3.44 Hz), the minimum output frequency at F1 or F2  
would be 0.0014% of 3.44 Hz or 4.81 × 10–5 Hz. This would be  
3.08 × 10–3 Hz at CF (64 × F1 Hz) when SCF = S0 = 1, S1 = 0.  
In this example, the no-load threshold would be equivalent to  
1.7 W of load or a start-up current of 8 mA at 220 V. Compare  
this value to the IEC 1036 specification which states that the  
meter must start up with a load equal to or less than 0.4% Ib.  
For a 5 A (Ib) meter, 0.4% of Ib is equivalent to 20 mA.  
*Values are generated using the nominal frequency of 450 kHz.  
When selecting a suitable F1–4 frequency for a meter design,  
the frequency output at IMAX (maximum load) with a meter con-  
stant of 100 imp/kWh should be compared with column four of  
Table V. The closest frequency in Table V will determine the  
best choice of frequency (F1–4). For example, if a meter with a  
maximum current of 25 A is being designed, the output fre-  
quency on F1 and F2 with a meter constant of 100 imp/kWh is  
0.153 Hz at 25 A and 220 V (from Table IV). Looking at Table V,  
the closest frequency to 0.153 Hz in column four is 0.176 Hz.  
Therefore, F3 (3.44 Hz—see Table I) is selected for this design.  
Frequency Outputs  
Figure 1 shows a timing diagram for the various frequency out-  
puts. The outputs F1 and F2 are the low frequency outputs that  
can be used to directly drive a stepper motor or electromechanical  
impulse counter. The F1 and F2 outputs provide two alter-  
nating low frequency pulses. The F1 and F2 pulse widths (t1)  
are set such that if they fall below 1062 ms (0.942 Hz) they are  
set to half of their period. The maximum output frequencies for  
F1 and F2 are shown in Table II.  
Negative Power Information  
The ADE7757 detects when the current and voltage channels  
have a phase shift greater than 90°. This mechanism can detect  
wrong connection of the meter or generation of negative power.  
The REVP pin output will go active high when negative power  
is detected and active low if positive power is detected. The  
REVP pin output changes state as a pulse is issued on CF. The  
REVP pin is not functional in the current version and will only  
work in the A version (ADE7757A).  
The high frequency CF output is intended to be used for com-  
munications and calibration purposes. CF produces a 173 ms wide  
active high pulse (t4) at a frequency proportional to active power.  
The CF output frequencies are given in Table III. As in the case  
of F1 and F2, if the period of CF (t5) falls below 346 ms, the  
–14–  
REV. A  
ADE7757  
OUTLINE DIMENSIONS  
16-Lead Standard Small Outline Package [SOIC]  
Narrow Body  
(RN-16)  
Dimensions shown in millimeters and (inches)  
10.00 (0.3937)  
9.80 (0.3858)  
16  
1
9
8
6.20 (0.2441)  
5.80 (0.2283)  
4.00 (0.1575)  
3.80 (0.1496)  
1.75 (0.0689)  
1.35 (0.0531)  
1.27 (0.0500)  
BSC  
0.50 (0.0197)  
0.25 (0.0098)  
45ꢀ  
0.25 (0.0098)  
0.10 (0.0039)  
8ꢀ  
0ꢀ  
0.51 (0.0201)  
0.31 (0.0122)  
SEATING  
PLANE  
1.27 (0.0500)  
0.40 (0.0157)  
0.25 (0.0098)  
0.17 (0.0067)  
COPLANARITY  
0.10  
COMPLIANT TO JEDEC STANDARDS MS-012AC  
CONTROLLING DIMENSIONS ARE IN MILLIMETERS; INCH DIMENSIONS  
(IN PARENTHESES) ARE ROUNDED-OFF MILLIMETER EQUIVALENTS FOR  
REFERENCE ONLY AND ARE NOT APPROPRIATE FOR USE IN DESIGN  
REV. A  
–15–  
ADE7757  
Revision History  
Location  
Page  
10/03—Data Sheet changed from REV. 0 to REV. A.  
Changes to FEATURES . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1  
Changes to GENERAL DESCRIPTION . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1  
Changes to ORDERING GUIDE . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 4  
Change to Typical Connection Diagrams section . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 10  
Updated OUTLINE DIMENSIONS . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 15  
–16–  
REV. A  

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