ANALOG DEVICES ADE7761B Service Manual

V

A

Energy Metering IC with On-Chip Fault and

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

FUNCTIONAL BLOCK DIAGRAM

AGND FAULT

PG

13

V

2

V

V

MISCAL

V

V

1A

4

1N

3

1B

7

6

2P

5

2N

2.5V

REFERENCE

3kΩ

ADC

ADC

ADC

ADC

A > B

B > A

A ≠ B

MISSING NEUTRAL

INTERNAL

OSCILLATOR

HPF

GAIN ADJUST

Missing Neutral Detection

ADE7761B

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
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

supply pin. Internal phase matching circuitry ensures

DD

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.

15 18

SUPPLY MONITOR

SIGNAL PROCESSING

ZERO-CROSSING

DETECTIO N

MISSING NE UTRAL

DETECTIO N

DIGITAL -TO-FREQUENCY CONVERT ER

ADE7751 by continuously

DD

POWER

ADE7761B

BLOCK

LPF

9 14 17 10 11 12

IN/OUT

16 18 19 20

F1F2CFREVPS0S1SCFDGNDRCLKINREF

06797-001

Figure 1.

Rev. 0

Information furnished by Analog Devices is believed to be accurate and reliable. However, no
responsibility is assumed by Anal og Devices for its use, nor for any infringements of patents or ot her
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: [phone] www.analog.com
Fax: [phone] ©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

VDD = 5 V ± 5%, AGND = DGND = 0 V, on-chip reference, on-chip oscillator, T

Table 1.

Parameter Value Unit Test Conditions/Comments

ACCURACY

Measurement Error

1

2

0.1 % of reading, typ Over a dynamic range of 1000 to 1

Phase Error Between Channels

PF = 0.8 Capacitive ±0.05 Degrees, max Phase lead 37°
PF = 0.5 Inductive ±0.05 Degrees, max Phase lag 60°

AC Power Supply Rejection

2

Output Frequency Variation 0.01 %, typ V1A = V1B = V2P = ±100 mV rms

DC Power Supply Rejection

2

Output Frequency Variation 0.01 %, typ V1A = V1B = V2P = ±100 mV rms

FAU LT D ETEC TION

2, 3

See the Fault Detection section

Fault Detection Threshold

Inactive Input ≠ Active Input 6.25 %, typ V1A or V1B active

Input Swap Threshold

Inactive Input ≠ Active Input 6.25 % of larger, typ V1A or V1B active

Accuracy Fault Mode Operation

V1A Active, V1B = AGND 0.1 % of reading, typ Over a dynamic range of 1000 to 1

V1B Active, V1A = AGND 0.1 % of reading, typ Over a dynamic range of 1000 to 1
Fault Detection Delay 3 Seconds, typ
Swap Delay 3 Seconds, typ

MISSING NEUTRAL MODE

2, 4

See the Missing Neutral Detection section

Missing Neutral Detection Threshold

V2P − V2N 59.4 mV peak, min
Accuracy Missing Neutral Mode

V1A Active, V1B = V2P = AGND 0.1 % of reading, typ Over a dynamic range of 500 to 1

V1B Active, V1A = V2P = AGND 0.1 % of reading, typ Over a dynamic range of 500 to 1
Missing Neutral Detection Delay 3 Seconds, typ

ANALOG INPUTS V1A − V1N, V1B − V1N, V2P − V2N

Maximum Signal Levels ±660 mV peak, max Differential input
660 mV peak, max Differential input MISCAL − V2N
Input Impedance (DC) 790 kΩ, min
Bandwidth (−3 dB) 7 kHz, typ
ADC Offset Error

2

15 mV, typ Uncalibrated error, see the Terminology section for details
Gain Error ±4 %, typ External 2.5 V reference
Gain Error Match

2

±3 %, typ External 2.5 V reference

REFERENCE INPUT

REF

Input Voltage Range 2.7 V, max 2.5 V + 8%

IN/OUT

2.3 V, min 2.5 V − 8%
Input Impedance 3 kΩ, min
Input Capacitance 10 pF, max

ON-CHIP REFERENCE

Reference Error ±200 mV, max
Temperature Coefficient 30 ppm/°C, typ
Current Source 10 µA, max Specification assures that V

ON-CHIP OSCILLATOR

Oscillator Frequency 450 kHz
Oscillator Frequency Tolerance ±12 % of reading, typ
Temperature Coefficient 30 ppm/°C, typ

MIN

to T

= −40°C to +85°C.

MAX

is within ±8%

REF

Specification achieved with 25 ppm/°C max resistor on the
RCLKIN pin

Rev. 0 | Page 3 of 24

ADE7761B

Parameter Value Unit Test Conditions/Comments

LOGIC INPUTS

PGA, SCF, S1, and S0

Input High Voltage, V
Input Low Voltage, V
Input Current, IIN ±3 µA, max Typical 10 nA, VIN = 0 V to VDD
Input Capacitance, CIN 10 pF, max

LOGIC OUTPUTS

CF, REVP, and FAULT

Output High Voltage, VOH 4 V, min VDD = 5 V ± 5%
Output Low Voltage, VOH 1 V, max VDD = 5 V ± 5%

F1 and F2

Output High Voltage, VOH 4 V, min VDD = 5 V ± 5%, I
Output Low Voltage, VOH 1 V, max VDD = 5 V ± 5%, I

POWER SUPPLY For specified performance

VDD 4.75 V, min 5 V − 5%

5.25 V, max 5 V + 5%
IDD 3.65 mA, max

1

See plots in the Typical Performance Characteristics section.

2

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

VDD = 5 V ± 5%, AGND = DGND = 0 V, on-chip reference, on-chip oscillator, T
initial release and after any redesign or process change that might affect this parameter. See

5

2.4 V, min VDD = 5 V ± 5%

INH

0.8 V, max VDD = 5 V ± 5%

INL

5

to T

MIN

= 10 mA

SOURCE

= 10 mA

SINK

= −40°C to +85°C. Sample tested during

MAX

Figure 2.

Table 2.

Parameter Value Unit Test Conditions/Comments

1

t

1

120 ms F1 and F2 pulse width (logic high)
t2 See Table 8 sec Output pulse period (see the Transfer Function section)
t3 1/2 t2 sec Time between F1 falling edge and F2 falling edge

1

t

4

90 ms CF pulse width (logic high)
t5 See Table 8 sec CF pulse period (see the Transfer Function section)
t6 CLKIN/4 sec Minimum time between F1 pulse and F2 pulse

1

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

t

2

t

F2

t

4

CF

3

t

5

06797-002

Figure 2. Timing Diagram for Frequency Outputs

Rev. 0 | Page 4 of 24

ADE7761B

ABSOLUTE MAXIMUM RATINGS

TA = 25°C, unless otherwise noted.

Table 3.

Parameter Rating

VDD to AGND −0.3 V to +7 V
Analog Input Voltage to AGND

V

, V1B, V1N, V2N, V2P, MISCAL

1A

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

Industrial −40°C to +85°C
Storage Temperature Range −65°C to +150°C
Junction Temperature 150°C
20-Lead SSOP, Power Dissipation 450 mW
θJA Thermal Impedance 112°C/W
Lead Temperature, Soldering

Vapor Phase (60 sec) 215°C

Infrared (15 sec) 220°C

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.

−6 V to +6 V

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 V2P − V2N complies with the conditions
described in
proportional to active power and can be used to bill active energy.

Case 2

When the analog input V2P − V2N does not comply with the
conditions described in
measure active energy but a quantity proportional to kiloampere­hours (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.

Figure 34, the CF, F1, and F2 frequencies are

Figure 34, the ADE7761B does not

ESD CAUTION

Rev. 0 | Page 5 of 24

ADE7761B

PIN CONFIGURATION AND FUNCTION DESCRIPTIONS

1

V

DD

2

V

1A

3

V

1B

V

4

1N

V

5

ADE7761B

MISCAL

REF

V

AGND

IN/OUT

SCF

2N

2P

6

7

8

9

10

TOP VIEW

(Not to Scale)

Figure 3. Pin Configuration (SSOP)

Table 4. Pin Function Descriptions

Pin No. Mnemonic Description

1 VDD

Power Supply. This pin provides the supply voltage for the digital circuitry in the ADE7761B. 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 V1A, V1B

Analog Inputs for Channel V1 (Current Channel). These inputs are fully differential voltage inputs with maximum
differential input signal levels of ±660 mV with respect to V
at these pins is ±1 V with respect to AGND. Both inputs have internal ESD protection circuitry, and an overvoltage
of ±6 V can also be sustained on these inputs without risk of permanent damage.

4 V1N

Negative Input for Differential Voltage Inputs, V
to AGND. The input has internal ESD protection circuitry, and an overvoltage of ±6 V can also be sustained on this
input without risk of permanent damage. The input should be directly connected to the burden resistor and held

5 V2N

at a fixed potential, that is, AGND. See the
Negative Input for Differential Voltage Inputs, V

Analog Inputs section.

respect to AGND. The input has internal ESD protection circuitry, and an overvoltage of ±6 V can also be sustained
on this input without risk of permanent damage. The input should be held at a fixed potential, that is, AGND. See
the

Analog Inputs section.

6 V2P

Analog Input for Channel V2 (Voltage Channel). This input is a fully differential voltage input with maximum
differential input signal levels of ±660 mV with respect to V
this pin is ±1 V with respect to AGND. This input has internal ESD protection circuitry, and an overvoltage of ±6 V
can also be sustained on this input without risk of permanent damage.

7 MISCAL

Analog Input for Missing Neutral Calibration. This pin can be used to calibrate the CF, F
missing neutral condition. This input is a fully differential voltage input with maximum differential input signal
levels of 660 mV with respect to V2N for specified operation. The maximum signal level at this pin is ±1 V with respect
to AGND. This input has internal ESD protection circuitry, and an overvoltage of ±6 V can also be sustained on this
input without risk of permanent damage.

8 AGND

Analog Ground. This pin provides the ground reference for the analog circuitry in the ADE7761B, that is, 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 such as antialiasing filters and current and voltage transducers. For good noise
suppression, the analog ground plane should be connected to the digital ground plane only at the DGND pin.

9 REF

IN/OUT

This pin provides access to the on-chip voltage reference. The on-chip reference has a nominal value of

2.5 V ± 8% and a typical temperature coefficient of 30 ppm/°C. An external reference source can also be
connected at this pin. In either case, this pin should be decoupled to AGND with a 1 F ceramic capacitor and
100 nF ceramic capacitor.

10 SCF

Select Calibration Frequency. This logic input is used to select the frequency on the Calibration Output CF.
Table 7 shows how the calibration frequencies are selected.

11, 12 S1, S0

These logic inputs are used to select one of four possible frequencies for the digital-to-frequency conversion.
This offers the designer greater flexibility when designing the energy meter. See the
Energy Meter Application

section.
13 PGA This logic input is used to select the gain for the analog inputs, V1A and V1B. The possible gains are 1 and 16.
14 RCLKIN

To enable the internal oscillator as a clock source on the chip, a precise low temperature drift resistor at
a nominal value of 6.2 kΩ must be connected from this pin to DGND.

20

F1

19

F2

18

CF

17

DGND

16

REVP

15

FAULT

14

RCLKIN

13

PGA

12

S0

11

S1

and V1B. The maximum signal level at this pin is ±1 V with respect

1A

and MISCAL. The maximum signal level at this pin is ±1 V with

2P

06797-003

for specified operation. The maximum signal level

1N

for specified operation. The maximum signal level at

2N

, and F2 frequencies in the

1

Selecting a Frequency for an

Rev. 0 | Page 6 of 24

ADE7761B

Pin No. Mnemonic Description

15 FAULT

16 REVP

17 DGND

18 CF

19, 20 F2, F1

This logic output goes active high when a fault or missing neutral condition occurs. A fault is defined as a
condition under which the signals on V
defined when the chip is powered up with no voltage at the input. The logic output is reset to 0 when a fault or
missing neutral condition is no longer detected. See the Fault Detection section and the Missing Neutral Mode
section.

This logic output goes logic high when negative power is detected, that is, when the phase angle between the
voltage and current signals is greater than 90°. This output is not latched and is reset when positive power is once
again detected. The output goes high or low at the same time that a pulse is issued on CF.

Digital Ground. This pin provides the ground reference for the digital circuitry in the ADE7761B, that is, multiplier,
filters, and digital-to-frequency converters. This pin should be tied to the digital ground plane of the PCB. The
digital ground plane is the ground reference for all digital circuitry, such as counters (mechanical and digital),
MCUs, and indicator LEDs. For good noise suppression, the analog ground plane should be connected to the digital
ground plane only at the DGND pin.

Calibration Frequency Logic Output. The CF logic output, active high, gives instantaneous active power information.
This output is used for operational and calibration purposes. See the

Low Frequency Logic Outputs. F1 and F2 supply average active power information. The logic outputs can be
used to directly drive electromechanical counters and 2-phase stepper motors.

and V1B differ by more than 6.25%. A missing neutral condition is

1A

Digital-to-Frequency Conversion section.

Rev. 0 | Page 7 of 24

ADE7761B

TYPICAL PERFORMANCE CHARACTERISTICS

1.0
PF = 1

ON-CHIP REFE RENCE

0.8

0.6

0.4

0.2

0

–0.2

% ERROR

–0.4

–0.6

–0.8

–1.0

CURRENT (% of Fu ll Scale)

–40°C

+25°C

+85°C

06797-004

1000.1 1 10

Figure 4. Active Power Error As a Percentage of Reading

with Gain = 1 and Internal Reference

1.0
PF = 1

ON-CHIP REFE RENCE

0.8

0.6

0.4

0.2

0

–0.2

% ERROR

–0.4

–0.6

–0.8

–1.0

+85°C; PF = 0.5

+25°C; PF = 0.5

CURRENT (% of Fu ll Scale)

–40°C; PF = 0.5

+25°C; PF = 1

1000.1 1 10

06797-005

Figure 5. Active Power Error As a Percentage of Reading
over Power Factor with Gain = 1 and Internal Reference

1.0
PF = 1, GAIN = 16

ON-CHIP REFE RENCE

0.8

0.6

0.4

0.2

0

–0.2

% ERROR

–0.4

–0.6

–0.8

–1.0

CURRENT (% of Fu ll Scale)

–40°C

+25°C

+85°C

1000.1 1 10

06797-006

Figure 6. Active Power Error As a Percentage of Reading

with Gain = 16 and Internal Reference

1.0
GAIN = 16

ON-CHIP REFERENCE

0.8

0.6

0.4

0.2

0

–0.2

% ERROR

–0.4

–0.6

–0.8

–1.0

CURRENT (% of Fu ll Scale)

PF = –0.5

PF = +1

Figure 7. Active Power Error As a Percentage of Reading

over Power Factor with Gain = 16 and Internal Reference

1.0
GAIN = 16

ON-CHIP REFERENCE

0.8

0.6

0.4

0.2

0

–0.2

% ERROR

–0.4

–0.6

–0.8

–1.0

CURRENT (% of Fu ll Scale)

Figure 8. Active Power Error As a Percentage of Reading
over Power Supply with Gain = 1 and Internal Reference

1.0
ON-CHIP REFERE NCE

0.8

0.6

0.4

0.2

0

–0.2

% ERROR

–0.4

–0.6

–0.8

–1.0

–40°C

CURRENT (% of Full Scal e)

+25°C

+85°C

Figure 9. Ampere Hour Error As a Percentage of Reading

in Missing Neutral Mode with Gain = 1 and Internal Reference

5.25V

5.00V

4.75V

PF = +0.5

1000.1 1 10

06797-007

1000.1 1 10

6797-108

1000.1 1 10

06797-109

Rev. 0 | Page 8 of 24