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Energy Metering IC with On-Chip Fault and
Missing Neutral Detection
ADE7761A
FEATURES
High accuracy, active energy measurement IC supports
IEC 62053-21
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 shunt and
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 ADE7761A is a high accuracy, fault-tolerant, electrical
energy measurement IC intended for use with 2-wire distribution
systems. The part specifications surpass the accuracy requirements
as quoted in the IEC 62053-21 standard. The only analog circuitry
used on the ADE7761A is in the ADCs and reference circuit.
All other signal processing (such as multiplication 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 ADE7761A incorporates a fault
detection scheme similar to the ADE7751 by continuously
monitoring both phase and neutral currents. A fault is indicated
when the currents differ by more than 6.25%.
The ADE7761A incorporates a missing neutral detection
scheme by continuously monitoring the input voltage. When a
missing neutral condition is detected—no voltage input—the
ADE7761A 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
ADE7761A supplies average active power information on the
low frequency outputs, F1 and F2. The CF logic output gives
instantaneous active power information.
The ADE7761A 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 ADE7761A does not exhibit
any creep when there is no load.
FAULT
15
FUNCTIONAL BLOCK DIAGRAM
PGA
13
AGND
8
V
DD
1
POWER
SUPPLY MONITOR
V
1A 2
V
1N 4
V
1B 3
MISCAL
7
V
2P 6
V
2N 5
ADC
B>A
A<>B
ZERO CROSSING
DETECTION
MISSING NEUTRAL
GAIN ADJUST
ADC
A>B
HPF
ADE7761A
SIGNAL PROCESSING
BLOCK
LPF
ADC
ADC
3kΩ
2.5V
REFERENCE
9
MISSING NEUTRAL
DETECTION
INTERNAL
OSCILLATOR
14
17
DIGITAL-TO-FREQUENCY CONVERTER
05040-0-001
10
11
12
16
18
19
20
REF
IN/OUT
RCLKIN
DGND
SCF
S1
S0 REVP CF
F2
F1
Figure 1.
Rev. 0
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.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, U.S.A.
Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2006 Analog Devices, Inc. All rights reserved.
ADE7761A
TABLE OF CONTENTS
Features .............................................................................................. 1
General Description ......................................................................... 1
Functional Block Diagram .............................................................. 1
Revision History ............................................................................... 2
Specifications..................................................................................... 3
Timing Characteristics ................................................................ 4
Absolute Maximum Ratings............................................................ 5
Performance
Issues That May Affect Billing Accuracy...........
5
ESD Caution.................................................................................. 5
Pin Configuration and Function Descriptions............................. 6
Terminology ...................................................................................... 8
Typical Performance Characteristics ............................................. 9
Test Circuit ...................................................................................... 10
Operation......................................................................................... 11
Power Supply Monitor ............................................................... 11
Analog Inputs ............................................................................. 11
Internal Oscillator ...................................................................... 12
Analog-to-Digital Conversion.................................................. 13
Active Power Calculation .......................................................... 14
Digital-to-Frequency Conversion ............................................ 16
Transfer Function....................................................................... 16
Fault Detection ........................................................................... 17
Missing Neutral Mode ............................................................... 18
Applications..................................................................................... 21
Interfacing to a Microcontroller for Energy Measurement .. 21
Selecting a Frequency for an Energy Meter Application ...... 21
Negative Power Information..................................................... 22
Outline Dimensions ....................................................................... 23
Ordering Guide .......................................................................... 23
REVISION HISTORY
7/06—Revision 0: Initial Version
Rev. 0 | Page 2 of 24
ADE7761A
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
Gain Error Match
2
REFERENCE INPUT
REF
IN/OUT
Input Voltage Range
Input Impedance
Input Capacitance
ON-CHIP REFERENCE
Reference Error
Temperature Coefficient
Current Source
ON-CHIP OSCILLATOR
Oscillator Frequency
Oscillator Frequency Tolerance
Temperature Coefficient
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
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
6.25
6.25
0.1
0.1
3
3
%, typ
% of larger, typ
% of reading, typ
% of reading, typ
Seconds, typ
Seconds, typ
See the Missing Neutral Detection section
59.4
0.1
0.1
3
±660
660
400
7
15
±4
±3
2.7
2.3
3
10
±200
30
20
450
±12
30
mV peak, min
% of reading, typ
% of reading, typ
Seconds, typ
mV peak, max
mV peak, max
kΩ, min
kHz, typ
mV, typ
%, typ
%, typ
V, max
V, min
kΩ, min
pF, max
mV, max
ppm/°C, typ
μA, min
kHz
% of reading, typ
ppm/°C, typ
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
External 2.5 V reference
2.5 V + 8%
2.5 V − 8%
Rev. 0 | Page 3 of 24
ADE7761A
Parameter
LOGIC INPUTS
5
PGA, SCF, S1, and S0
Input High Voltage, V
INH
Input Low Voltage, V
INL
Input Current, I
IN
Input Capacitance, C
IN
LOGIC OUTPUTS
5
CF, REVP, and FAULT
Output High Voltage, V
OH
Output Low Voltage, V
OH
F1 and F2
Output High Voltage, V
OH
Output Low Voltage, V
OH
POWER SUPPLY
V
DD
V
DD
1
2
Value
Unit
Test Conditions/Comments
2.4
0.8
±3
10
V, min
V, max
μA, max
pF, max
V
DD
= 5 V ± 5%
V
DD
= 5 V ± 5%
Typical 10 nA, V
IN
= 0 V to V
DD
4
1
4
1
4.75
5.25
3
V, min
V, max
V, min
V, max
V, min
V, max
mA, max
V
DD
= 5 V ± 5%
V
DD
= 5 V ± 5%
V
DD
= 5 V ± 5%, I
SOURCE
= 10 mA
V
DD
= 5 V ± 5%, I
SINK
= 10 mA
For specified performance
5 V − 5%
5 V + 5%
See plots in the Typical Performance Characteristics section.
See the Terminology section for explanation of specifications.
3
See the Fault Detection section for explanation of fault detection functionality.
4
See the Missing Neutral Detection section for explanation of missing neutral detection functionality.
5
Sample tested during initial release and after any redesign or process change that might affect this parameter.
TIMING CHARACTERISTICS
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. Sample tested during
initial release and after any redesign or process change that might affect this parameter. See Figure 2.
Table 2.
Parameter
t
1 1
t
2
t
3
t
41
t
5
t
6
1
Value
120
See Table 7
1/2 t
2
90
See Table 8
CLKIN/4
Unit
ms
s
s
ms
s
s
Test Conditions/Comments
F1 and F2 Pulse Width (Logic High).
Output Pulse Period. See the Transfer Function section.
Time Between F1 Falling Edge and F2 Falling Edge.
CF Pulse Width (Logic High).
CF Pulse Period. See the Transfer Function section.
Minimum Time Between F1 and F2 Pulse.
The pulse widths of F1, F2, and CF are not fixed for higher output frequencies. See the Transfer Function section.
t
1
F1
t
6
F2
t
2
t
3
05040-002
t
4
CF
t
5
Figure 2. Timing Diagram for Frequency Outputs
Rev. 0 | Page 4 of 24
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