Energy Metering IC with On-Chip Fault and
Missing Neutral Detection
ADE7761B
FEATURES
High accuracy, active energy measurement IC supports
IEC 62053-21
Less than 0.1% error over a dynamic range of 1000 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 channel 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 ADE7761B 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 ADE7761B 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 ADE7761B 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 ADE7761B incorporates a missing neutral detection scheme
by continuously monitoring the input voltage. When a missing
neutral condition is detected (no voltage input), the ADE7761B
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 ADE7761B
supplies average active power information on the low frequency
outputs, F1 and F2. The CF logic output gives instantaneous
active power information.
The ADE7761B 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 ADE7761B 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
ADE7761B
SIGNAL PROCESSING
BLOCK
LPF
ADC
ADC
3kΩ
2.5V
REFERENCE
9
MISSING NEUTRAL
DETECTION
INTERNAL
OSCILLATOR
14
17
DIGITAL-TO-FREQUENCY CONVERTER
06797-001
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
©2007 Analog Devices, Inc. All rights reserved.
ADE7761B
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
Typical Performance Characteristics ............................................. 8
Test Circuit ........................................................................................ 9
Terminology .................................................................................... 10
Theory of 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 Information .............................................................. 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
8/07—Revision 0: Initial Version
Rev. 0 | Page 2 of 24
ADE7761B
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 1000 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 1000 to 1
Over a dynamic range of 1000 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
790
7
15
±4
±3
2.7
2.3
3
10
±200
30
10
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, max
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%
Specification assures that V
REF
is within ±8%
Specification achieved with 25 ppm/°C max resistor on the
RCLKIN pin
Rev. 0 | Page 3 of 24
ADE7761B
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
I
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
3.65
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 8
1/2 t
2
90
See Table 8
CLKIN/4
Unit
ms
sec
sec
ms
sec
sec
Test Conditions/Comments
F
1
and F
2
pulse width (logic high)
Output pulse period (see the Transfer Function section)
Time between F
1
falling edge and F
2
falling edge
CF pulse width (logic high)
CF pulse period (see the Transfer Function section)
Minimum time between F
1
pulse and F
2
pulse
The pulse widths of F1, F2, and CF are not fixed for higher output frequencies. See the Transfer Function section.
Timing Diagram
t
1
F1
t
6
F2
t
2
t
3
06797-002
t
4
CF
t
5
Figure 2. Timing Diagram for Frequency Outputs
Rev. 0 | Page 4 of 24
ADE7761B
ABSOLUTE MAXIMUM RATINGS
T
A
= 25°C, unless otherwise noted.
Table 3.
Parameter
V
DD
to AGND
Analog Input Voltage to AGND
V
1A
, V
1B
, V
1N
, V
2N
, V
2P
, MISCAL
Reference Input Voltage to AGND
Digital Input Voltage to DGND
Digital Output Voltage to DGND
Operating Temperature Range
Industrial
Storage Temperature Range
Junction Temperature
20-Lead SSOP, Power Dissipation
θ
JA
Thermal Impedance
Lead Temperature, Soldering
Vapor Phase (60 sec)
Infrared (15 sec)
Rating
−0.3 V to +7 V
−6 V to +6 V
−0.3 V to V
DD
+ 0.3 V
−0.3 V to V
DD
+ 0.3 V
−0.3 V to V
DD
+ 0.3 V
−40°C to +85°C
−65°C to +150°C
150°C
450 mW
112°C/W
215°C
220°C
PERFORMANCE ISSUES THAT MAY AFFECT
BILLING ACCURACY
The ADE7761B provides pulse outputs, CF, F1, and F2, that are
intended to be used for the billing of active energy. Pulses are
generated at these outputs in two different situations.
Case 1
When the analog input V
2P
− V
2N
complies with the conditions
described in Figure 34, the CF, F
1
, and F
2
frequencies are
proportional to active power and can be used to bill active energy.
Case 2
When the analog input V
2P
− V
2N
does not comply with the
conditions described in Figure 34, the ADE7761B does not
measure active energy but a quantity proportional to kiloampere-
hours (kAh). This quantity is used to generate pulses on the
same CF, F1, and F2. This situation is indicated when the
FAULT pin is high.
Analog Devices, Inc., cautions users of the ADE7761B about the
following:
•
Billing active energy in Case 1 is consistent with the under-
standing of the quantity represented by pulses on the CF, F1,
and F2 outputs (watthour).
•
Billing active energy while the ADE7761B is in Case 2 must
be decided knowing that the entity measured by the ADE7761B
in this case is ampere-hour and not watthour. Users should
be aware of this limitation and decide if the ADE7761B is
appropriate for their application.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
ESD CAUTION
Rev. 0 | Page 5 of 24
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