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Energy Metering IC with On-Chip
Fault and Missing Neutral Detection
ADE7761
FEATURES
High accuracy active energy measurement IC, supports
IEC 687/61036
Less than 0.1% error over a dynamic range of 500 to 1
Supplies active power on the frequency outputs F1 and F2
High frequency output CF is intended for calibration and
supplies instantaneous active power
Continuous monitoring of the phase and neutral current
allows fault detection in 2-wire distribution systems
Current channels input level best suited for current
transformer sensors
Uses the larger of the two currents (phase or neutral) to
bill—even during a fault condition
Continuous monitoring of the voltage and current inputs
allows missing neutral detection
Uses one current input (phase or neutral) to bill when
missing neutral is detected
Two logic outputs (FAULT and REVP) can be used to indicate
a potential miswiring, fault, or missing neutral condition
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
Reference 2.5 V ± 8% (drift 30 ppm/°C typical) with external
overdrive capability
Single 5 V supply, low power
GENERAL DESCRIPTION
The ADE7761 is a high accuracy, fault tolerant, electrical energy
measurement IC intended for use with 2-wire distribution
systems. The part specifications surpass the accuracy require-
ments as quoted in the IEC61036 standard.
The only analog circuitry used on the ADE7761 is in the ADCs
and reference circuit. All other signal processing (such as multi-
plication and filtering) is carried out in the digital domain. This
approach provides superior stability and accuracy over extremes
in environmental conditions and over time.
The ADE7761 incorporates a fault detection scheme similar to
the ADE7751 by continuously monitoring both the phase and
neutral currents. A fault is indicated when these currents differ
by more than 6.25%.
(continued on Page 3)
SO
AGND
8
15
FUNCTIONAL BLOCK DIAGRAM
FAULT
V
DD
1
B
V
1A 2
V
1N 4
V
1B 3
ADC
ADC
LE
A>B
HPF
B>A
A<>B
ZERO CROSSING
DETECTION
MISSING NEUTRAL
GAIN ADJUST
MISSING NEUTRAL
DETECTION
14
17
10
11
12
O
MISCAL
7
V
2P 6
ADC
ADC
V
2N 5
4kΩ
2.5V
REFERENCE
INTERNAL
OSCILLATOR
9
16
18
19
20
REF
IN/OUT
RCLKIN
DGND
SCF
S1
S0 REVP CF
F2
F1
Figure 1.
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, nor for any
infringements of patents or other rights of third parties that may result from its use.
Specifications subject to change without notice. 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.
04407-0-001
TE
POWER
SUPPLY MONITOR
ADE7761
SIGNAL PROCESSING
BLOCK
LPF
DIGITAL-TO-FREQUENCY CONVERTER
.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.326.8703
© 2004 Analog Devices, Inc. All rights reserved.
ADE7761
TABLE OF CONTENTS
General Description ......................................................................... 3
Specifications..................................................................................... 4
Timing Characteristics..................................................................... 6
Absolute Maximum Ratings............................................................ 7
ESD Caution.................................................................................. 7
Terminology ...................................................................................... 8
Pin Configuration and Function Descriptions............................. 9
Typical Performance Characteristics ........................................... 11
Operation......................................................................................... 13
Power Supply Monitor ............................................................... 13
Analog Inputs.............................................................................. 13
Internal Oscillator ...................................................................... 14
Active Power Calculation .......................................................... 15
Digital-to-Frequency Conversion ............................................ 18
Transfer Function....................................................................... 18
Fault Detection ........................................................................... 19
Missing Neutral Mode ............................................................... 20
Applications..................................................................................... 23
Interfacing to a Microcontroller for Energy Measurement .. 23
Selecting a Frequency for an Energy Meter Application....... 23
Negative Power Information..................................................... 24
Outline Dimensions ....................................................................... 25
Ordering Guide .......................................................................... 25
Disclaimer........................................................................................ 26
Analog-to-Digital Conversion.................................................. 14
REVISION HISTORY
2/04—Changed from Rev. 0 to Rev. A.
Changes to Ordering Guide .......................................................... 25
1/04—Revision 0: Initial Version
O
Rev. A | Page 2 of 28
B
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ADE7761
GENERAL DESCRIPTION
(continued from Page 1)
The ADE7761 incorporates a missing neutral detection scheme
by continuously monitoring the input voltage. When a missing
neutral condition is detected—no voltage input—the ADE7761
continues billing based on the active current signal (see the
Missing Neutral Mode section). The missing neutral condition
is indicated when the FAULT pin goes high.
The ADE7761 supplies average active power information on the
low frequency outputs F1 and F2. The CF logic output gives
instantaneous active power information.
The ADE7761 includes a power supply monitoring circuit on
the V
DD
supply pin. Internal phase matching circuitry ensures
that the voltage and current channels are matched. An internal
no-load threshold ensures that the ADE7761 does not exhibit
any creep when there is no load.
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Rev. A | Page 3 of 28
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ADE7761
SPECIFICATIONS
V
DD
= 5 V ± 5%, AGND = DGND = 0 V, on-chip reference, on-chip oscillator, T
MIN
to T
MAX
= –40°C to +85°C.
Table 1.
Parameter
ACCURACY
1
Measurement Error
2
Phase Error between Channels
(PF = 0.8 Capacitive)
(PF = 0.5 Inductive)
AC Power Supply Rejection
2
Output Frequency Variation
DC Power Supply Rejection
2
Output Frequency Variation
FAULT DETECTION
2, 3
Fault Detection Threshold
Inactive Input <> Active Input
Input Swap Threshold
Inactive Input <> Active Input
Accuracy Fault Mode Operation
V
1A
Active, V
1B
= AGND
V
1B
Active, V
1A
= AGND
Fault Detection Delay
Swap Delay
MISSING NEUTRAL MODE
2, 4
Missing Neutral Detection Threshold
V
2P
− V
2N
Accuracy Missing Neutral Mode
V
1A
Active, V
1B
= V
2P
= AGND
V
1B
Active, V
1A
= V
2P
= AGND
Missing Neutral Detection Delay
ANALOG INPUTS
Maximum Signal Levels
Input Impedance (DC)
Bandwidth (−3 dB)
ADC Offset Error
2
Gain Error
REFERENCE INPUT
REF
IN/OUT
Input Voltage Range
Value
0.1
±0.05
±0.05
0.01
0.01
Unit
% of reading, typ
Degrees, max
Degrees, max
%, typ
%, typ
Test Conditions/Comments
Over a dynamic range of 500 to 1
Phase lead 37°
Phase lag 60°
V
1A
= V
1B
= V
2P
= ±100 mV rms
6.25
6.25
0.1
0.1
3
3
%, typ
% of larger, typ
% of reading, typ
% of reading, typ
Seconds, typ
Seconds, typ
SO
0.1
0.1
3
% of reading, typ
% of reading, typ
Seconds, typ
mV peak, max
mV peak, max
kΩ, min
kHz, typ
mV, max
%, typ
V, max
V, min
kΩ, min
pF, max
mV, max
ppm/°C, typ
µA, min
kHz
% of reading, typ
ppm/°C, typ
±660
660
400
7
10
±4
2.7
2.3
4
10
±200
30
20
450
±12
30
Rev. A | Page 4 of 28
59.4
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Input Impedance
Input Capacitance
ON-CHIP REFERENCE
Reference Error
Temperature Coefficient
Current Source
ON-CHIP OSCILLATOR
Oscillator Frequency
Oscillator Frequency Tolerance
Temperature Coefficient
See footnotes on next page.
LE
mV peak, min
2.5 V + 8%
2.5 V − 8%
TE
V
1A
= V
1B
= V
2P
= ±100 mV rms
See the Fault Detection section
(V
1A
or V
1B
active)
(V
1A
or V
1B
active)
Over a dynamic range of 500 to 1
Over a dynamic range of 500 to 1
See the Missing Neutral Detection section
Over a dynamic range of 500 to 1
Over a dynamic range of 500 to 1
V
1A
− V
1N
, V
1B
− V
1N
, V
2P
− V
2N
Differential input
Differential input MISCAL − V
2N
Uncalibrated error, see the Terminology section for details
External 2.5 V reference
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