3-Phase, 3-Wire, and 4-Wire
Energy Metering IC with Pulse Output
ADE7752B
FEATURES
The only analog circuitry used in the ADE7752B is in the
analog-to-digital converters (ADCs) and reference circuit. All
other signal processing (for example, multiplication, filtering,
and summation) is carried out in the digital domain. This
approach provides superior stability and accuracy over
extremes in environmental conditions and over time.
The ADE7752B supplies average active power information on
the low frequency outputs, F1 and F2. These logic outputs can
be used to directly drive an electromechanical counter or to
interface with a microcontroller (MCU). The CF logic output
gives instantaneous active power information. This output is
intended to be used for calibration purposes.
The ADE7752B includes a power supply monitoring circuit on
the VDD pin. The ADE7752B remains inactive until the supply
voltage on VDD reaches 4 V. If the supply falls below 4 V, the
ADE7752B resets and no pulses are issued on F1, F2, and CF.
Internal phase matching circuitry ensures that the voltage and
current channels are phase matched. An internal no load
threshold ensures that the ADE7752B does not exhibit any
creep when there is no load.
The ADE7752B is available in a 24-lead SOIC package.
High accuracy supports 50 Hz/60 Hz IEC 62053-21
Less than 0.1% error over a dynamic range of 500 to 1
Compatible with 3-phase, 3-wire delta and 3-phase, 4-wire
Wye configurations
Supplies average active power on the frequency outputs F1
and F2
High frequency output (CF) is intended for calibration and
supplies instantaneous active power
Logic output REVP indicates a potential miswiring or
negative power on the sum of all phases
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
On-chip power supply monitoring
On-chip creep protection (no load threshold)
On-chip reference 2.4 V ± 8% (25 ppm/°C typical) with
external overdrive capability
Single 5 V supply, low power (42.5 mW typical)
Low cost CMOS process
GENERAL DESCRIPTION
The ADE7752B is a high accuracy polyphase electrical energy
measurement IC. The ADE7752B specifications surpass the
accuracy requirements as quoted in the IEC62053-21 standard.
FUNCTIONAL BLOCK DIAGRAM
IAP 5
ADC
IAN 6
VAP 16
ADC
HPF
LPF
ABS
VDD
17
3
X
POWER
SUPPLY
MONITOR
Ф
ADE7752B
IBP
7
IBN
8
ADC
X
HPF
VBP 15
ADC
2
LPF
Ф
DGND
19 CLKIN
20 CLKOUT
ADC
ICN 10
VCP 14
ADC
VN 13
2.4V REF
HPF
X
LPF
Ф
4kΩ
DIGITAL-TO-FREQUENCY CONVERTER
11
12
AGND
REFIN/OUT
4
18
REVP SCF
22
21
23
24
1
S1
S0
F2
F1
CF
05905-001
ICP 9
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
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Tel: 781.329.4700
www.analog.com
Fax: 781.461.3113
©2007 Analog Devices, Inc. All rights reserved.
ADE7752B
TABLE OF CONTENTS
Features .............................................................................................. 1
Voltage Channels........................................................................ 13
General Description ......................................................................... 1
Typical Connection Diagrams...................................................... 14
Functional Block Diagram .............................................................. 1
Current Channel Connection................................................... 14
Revision History ............................................................................... 2
Voltage Channel Connection.................................................... 14
Specifications..................................................................................... 3
Meter Connections..................................................................... 14
Timing Characteristics ................................................................ 4
Power Supply Monitor ................................................................... 16
Absolute Maximum Ratings............................................................ 5
HPF and Offset Effects .................................................................. 17
ESD Caution.................................................................................. 5
Digital-to-Frequency Conversion ................................................ 18
Pin Configuration and Function Descriptions............................. 6
Accumulation of 3-Phase Power .............................................. 19
Typical Performance Characteristics ............................................. 8
Transfer Function ........................................................................... 20
Terminology ...................................................................................... 9
Frequency Outputs F1 and F2 .................................................. 20
Test Circuit ...................................................................................... 10
Frequency Output CF ................................................................ 21
Theory of Operation ...................................................................... 11
Selecting a Frequency for an Energy Meter Application........... 22
Power Factor Considerations.................................................... 11
Frequency Outputs..................................................................... 22
Nonsinusoidal Voltage and Current ........................................ 12
No-Load Threshold.................................................................... 23
Analog Inputs.................................................................................. 13
Outline Dimensions ....................................................................... 24
Current Channels ....................................................................... 13
Ordering Guide .......................................................................... 24
REVISION HISTORY
8/07—Revision 0: Initial Version
Rev. 0 | Page 2 of 24
ADE7752B
SPECIFICATIONS
VDD = 5 V ± 5%, AGND = DGND = 0 V, on-chip reference, CLKIN = 10 MHz, TMIN to TMAX = −40°C to +85°C, unless otherwise noted.
Table 1.
Parameter
ACCURACY1, 2
Measurement Error on Current
Channel
Phase Error Between Channels
PF = 0.8 Capacitive
PF = 0.5 Capacitive
AC Power Supply Rejection
Output Frequency Variation (CF)
DC Power Supply Rejection
Output Frequency Variation (CF)
ANALOG INPUTS
Maximum Signal Levels
Input Impedance (DC)
Bandwidth (−3 dB)
ADC Offset Error1, 2
Gain Error
REFERENCE INPUT
REFIN/OUT Input Voltage Range
Input Impedance
Input Capacitance
ON-CHIP REFERENCE
Reference Error
Temperature Coefficient
CLKIN (INPUT CLOCK FREQUENCY)
LOGIC INPUTS3
SCF, S0, S1, and ABS
Input High Voltage, VINH
Input Low Voltage, VINL
Input Current, IIN
Input Capacitance, CIN
LOGIC OUTPUTS3
F1 and F2
Output High Voltage, VOH
Output Low Voltage, VOL
CF and REVP
Output High Voltage, VOH
Output Low Voltage, VOL
POWER SUPPLY
VDD
IDD
1
2
3
Conditions
Min
Typ
Max
0.1
Voltage channel with full-scale signal (±500 mV), 25°C,
over a dynamic range of 500 to 1
% reading
±0.1
±0.1
SCF = 0, S0 = S1 = 1
IA = IB = IC = 100 mV rms,
VA = VB = VC = 100 mV rms @ 50 Hz,
Ripple on VDD of 200 mV rms @ 100 Hz
S1 = 1, S0 = SCF = 0
V1 = 100 mV rms, V2 = 100 mV rms,
VDD = 5 V ± 250 mV
See the Analog Inputs section
VAP – VN, VBP – VN, VCP – VN, IAP – IAN, IBP – IBN, ICP – ICN
CLKIN = 10 MHz
CLKIN/256, CLKIN = 10 MHz
% reading
0.1
% reading
590
14
±25
External 2.5 V reference, IA = IB = IC = 500 mV dc
2.4 V + 8%
2.4 V − 8%
Degrees
Degrees
0.01
±0.5
500
Unit
±9
2.6
2.2
3.3
10
V peak
difference
kΩ
kHz
mV
% ideal
V
V
kΩ
pF
Nominal 2.4 V
±200
25
10
All specifications for CLKIN of 10 MHz
VDD = 5 V ± 5%
VDD = 5 V ± 5%
Typically 10 nA, VIN = 0 V to VDD
2.4
ISOURCE = 10 mA, VDD = 5 V
ISINK = 10 mA, VDD = 5 V
4.5
VDD = 5 V, ISOURCE = 5 mA
VDD = 5 V, ISINK = 5 mA
For specified performance
5 V ± 5%
4.5
4.75
8.5
See the Terminology section for explanation of specifications.
See the plots in the Typical Performance Characteristics section.
Sample tested during initial release and after any redesign or process changes that might affect this parameter.
Rev. 0 | Page 3 of 24
mV
ppm/°C
MHz
0.8
±3
10
V
V
μA
pF
0.5
V
V
0.5
V
V
5.25
10
V
mA
ADE7752B
TIMING CHARACTERISTICS
VDD = 5 V ± 5%, AGND = DGND = 0 V, on-chip reference, CLKIN = 10 MHz, TMIN to TMAX = −40°C to +85°C, unless otherwise noted.
Table 2.
Parameter1,2
t1 3
t2
t3
t43, 4
t55
t6
Conditions
F1 and F2 pulse width (logic high)
Output pulse period (see the Transfer Function section)
Time between F1 rising edge and F2 rising edge
CF pulse width (logic high)
CF pulse period (see the Transfer Function section)
Minimum time between F1 and F2 pulse
Specification
120
See Figure 2
½ t2
90
See Table 7
4/CLKIN
1
Sample tested during initial release and after any redesign or process changes that might affect this parameter.
See Figure 2.
3
The pulse widths of F1, F2, and CF are not fixed for higher output frequencies (see the Frequency Outputs section).
4
CF is not synchronous to F1 or F2 frequency outputs.
5
The CF pulse is always 1 μs in the high frequency mode (see the Frequency Outputs section).
2
t1
F1
t6
t2
t3
t4
t5
05905-002
F2
CF
Figure 2. Timing Diagram for Frequency Outputs
Rev. 0 | Page 4 of 24
Unit
ms
sec
sec
ms
sec
sec
ADE7752B
ABSOLUTE MAXIMUM RATINGS
TA = 25°C, unless otherwise noted.
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.
Table 3.
Parameter
VDD to AGND
VDD to DGND
Analog Input Voltage to AGND
VAP, VBP, VCP, VN, IAP, IAN, IBP, IBN, ICP,
and ICN
Reference Input Voltage to AGND
Digital Input Voltage to DGND
Digital Output Voltage to DGND
Operating Temperature Range, Industrial
Storage Temperature Range
Junction Temperature
24-Lead SOIC, Power Dissipation
θJA Thermal Impedance
Lead Temperature, Soldering
Vapor Phase (60 sec)
Infrared (15 sec)
Rating
−0.3 V to +7 V
−0.3 V to +7 V
−6 V to +6 V
−0.3 V to VDD + 0.3 V
−0.3 V to VDD + 0.3 V
−0.3 V to VDD + 0.3 V
−40°C to +85°C
−65°C to +150°C
150°C
63 mW
55°C/W
ESD CAUTION
215°C
220°C
Rev. 0 | Page 5 of 24
ADE7752B
PIN CONFIGURATION AND FUNCTION DESCRIPTIONS
CF 1
24 F1
DGND 2
23 F2
VDD 3
22 S1
21 S0
IAP 5
ADE7752B
20 CLKOUT
IAN 6
TOP VIEW
(Not to Scale)
19 CLKIN
IBP 7
18 SCF
IBN 8
17 ABS
ICP 9
16 VAP
ICN 10
15 VBP
AGND 11
14 VCP
REFIN/OUT 12
13 VN
05905-004
REVP 4
Figure 3. Pin Configuration
Table 4. Pin Function Descriptions
Pin No.
1
Mnemonic
CF
2
DGND
3
VDD
4
REVP
5, 6;
7, 8;
9, 10
IAP, IAN;
IBP, IBN;
ICP, ICN
11
AGND
12
REFIN/OUT
13, 14, 15,
16
VN, VCP, VBP, VAP
17
ABS
18
SCF
19
CLKIN
Description
Calibration Frequency Logic Output. The CF logic output gives instantaneous active power information.
This output is intended to be used for calibration purposes.
This provides the ground reference for the digital circuitry in the ADE7752B, that is, multipliers, filters,
and digital-to-frequency converters. Because the digital return currents in the ADE7752B are small, it is
acceptable to connect this pin to the analog ground plane of the whole system.
Power Supply. This pin provides the supply voltage for the digital circuitry in the ADE7752B. The supply
voltage should be maintained at 5 V ± 5% for specified operation. This pin should be decoupled to
DGND with a 10 μF capacitor in parallel with a 100 nF ceramic capacitor.
This logic output goes logic high when negative power is detected on the sum of the three phase
powers. This output is not latched and resets when positive power is once again detected (see the
Negative Total Power Detection section).
Analog Inputs for Current Channels. These channels are intended for use with current transducers and
are referenced in this document as current channels. These inputs are fully differential voltage inputs
with maximum differential input signal levels of ±0.5 V (see the Analog Inputs section). Both inputs
have internal ESD protection circuitry; in addition, an overvoltage of ±6 V can be sustained on these
inputs without risk of permanent damage.
This pin provides the ground reference for the analog circuitry in the ADE7752B (ADCs and reference).
This pin should be tied to the analog ground plane or the quietest ground reference in the system. This
quiet ground reference should be used for all analog circuitry, such as antialiasing filters and current
and voltage transducers. To keep ground noise around the ADE7752B to a minimum, the quiet ground
plane should connect to the digital ground plane at only one point. It is acceptable to place the entire
device on the analog ground plane.
This pin provides access to the on-chip voltage reference. The on-chip reference has a nominal value of
2.4 V ± 8% and a typical temperature coefficient of 25 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 μF ceramic
capacitor.
Analog Inputs for the Voltage Channels. These channels are intended for use with voltage transducers
and are referenced in this document as voltage channels. These inputs are single-ended voltage inputs
with a maximum signal level of ±0.5 V with respect to VN for specified operation. All inputs have
internal ESD protection circuitry; in addition, an overvoltage of ±6 V can be sustained on these inputs
without risk of permanent damage.
This logic input is used to select the method by which the three active energies from each phase are
summed. It selects between the arithmetical sum of the three energies (ABS logic high) or the sum of
the absolute values (ABS logic low). See the Mode Selection of the Sum of the Three Active Energies section.
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.
Master Clock for the ADCs and Digital Signal Processing. An external clock can be provided at this logic
input. Alternatively, a parallel resonant AT crystal can be connected across CLKIN and CLKOUT to
provide a clock source for the ADE7752B. The clock frequency for the specified operation is 10 MHz.
Ceramic load capacitors between 22 pF and 33 pF should be used with the gate oscillator circuit. Refer
to the crystal manufacturer’s data sheet for the load capacitance requirements.
Rev. 0 | Page 6 of 24
ADE7752B
Pin No.
20
Mnemonic
CLKOUT
21, 22
S0, S1
23, 24
F2, F1
Description
A crystal can be connected across this pin and CLKIN as described for Pin 19 to provide a clock source
for the ADE7752B. The CLKOUT pin can drive one CMOS load when an external clock is supplied at
CLKIN or when a crystal is used.
These logic inputs are used to select one of four possible frequencies for the digital-to-frequency
conversion for design flexibility.
Low Frequency Logic Outputs. F1 and F2 supply average active power information. These logic outputs
can be used to drive electromechanical counters and 2-phase stepper motors directly (see the Transfer
Function section).
Rev. 0 | Page 7 of 24
ADE7752B
TYPICAL PERFORMANCE CHARACTERISTICS
0.5
0.5
0.4
0.4
PHASE C
0.3
0.2
PHASE B
0
–0.1
–0.2
PHASE A
+85°C, POWER FACTOR = 1
0
–0.1
–40°C, POWER FACTOR = 1
–0.2
–0.3
05905-007
–0.3
–0.4
–0.5
0.1
+25°C, POWER FACTOR = 1
0.1
1
10
05905-010
0.1
0.3
PHASE A + B + C
% ERROR
% ERROR
0.2
–0.4
–0.5
0.1
100
1
10
100
CURRENT CHANNEL (% of Full Scale)
CURRENT CHANNEL (% of Full Scale)
Figure 4. Error As a Percent of Reading
with Internal Reference (Wye Connection)
Figure 7. Error As a Percent of Reading over Temperature
with External Reference (Wye Connection)
1.0
1.0
0.8
0.5
–40°C, POWER FACTOR = 0.5
% ERROR
% ERROR
0.6
0.4
0.2
+25°C, POWER FACTOR = 1
0
POWER FACTOR = 1
POWER FACTOR = 0.5
–0.5
0
1
10
05905-008
+85°C, POWER FACTOR = 0.5
–0.4
0.1
05905-011
–1.0
+25°C, POWER FACTOR = 0.5
–0.2
–1.5
45
100
50
0.4
0.4
0.2
0.2
0.1
% ERROR
0.3
+25°C, POWER FACTOR = 1
–0.2
–0.5
4.75V
0
5.25V
1
10
05905-012
–0.3
–0.8
–1.0
0.1
5V
–0.1
–0.2
+85°C, POWER FACTOR = 1
05905-009
% ERROR
–40°C, POWER FACTOR = 1
0.6
–0.4
65
0.5
1.0
0
60
Figure 8. Error As a Percent of Reading over Frequency
with an Internal Reference (Wye Connection)
Figure 5. Error As a Percent of Reading over Power Factor
with Internal Reference (Wye Connection)
0.8
55
LINE FREQUENCY (Hz)
CURRENT CHANNEL (% of Full Scale)
–0.4
–0.5
0.1
100
1
10
CURRENT CHANNEL (% of Full Scale)
CURRENT CHANNEL (% of Full Scale)
Figure 9. Error As a Percent of Reading over Power Supply
with Internal Reference (Wye Connection)
Figure 6. Error As a Percent of Reading over Temperature
with Internal Reference (Wye Connection)
Rev. 0 | Page 8 of 24
100
ADE7752B
TERMINOLOGY
Measurement Error
The error associated with the energy measurement made by the
ADE7752B is defined by the following formula:
Percentage Error =
⎛ Energy Registered by ADE7762 – True Energy ⎞
⎜
⎟ × 100% (1)
⎜
⎟
True Energy
⎝
⎠
Error Between Channels
The high-pass filter (HPF) in the current channel has a phase
lead response. To offset this phase response and equalize the
phase response between channels, a phase correction network
is placed in the current channel. The phase correction network
ensures a phase match between the current channels and the
voltage channels to within ±0.1° over a range of 45 Hz to 65 Hz
and ±0.2° over a range of 40 Hz to 1 kHz (see Figure 21 and
Figure 22).
ADC Offset Error
This refers to the dc offset associated with the analog inputs to
the ADCs. It means that with the analog inputs connected to
AGND, the ADCs still see an analog input signal offset.
However, because the HPF is always present, the offset is
removed from the current channel and the power calculation is
not affected by this offset.
Gain Error
The gain error of the ADE7752B 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 ADE7752B transfer function (see the
Transfer Function section).
Power Supply Rejection (PSR)
This quantifies the ADE7752B measurement error as a
percentage of reading when the power supplies are varied.
For the ac PSR measurement, a reading at a nominal supply
(5 V) is taken. A 200 mV rms/100 Hz signal is then introduced
onto the supply and a second reading is obtained under the
same input signal levels. Any error introduced is expressed as a
percentage of reading. See the definition for Measurement Error.
For the dc PSR measurement, a reading at nominal supplies
(5 V) is taken. The supply is 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.
Rev. 0 | Page 9 of 24
ADE7752B
TEST CIRCUIT
VDD
100nF
3
1kΩ
Rb
5
ADE7752B
IAN
SAME AS
IAP, IAN
1MΩ
220V
AC
1kΩ
33nF
3
IBP
8
IBN
9
ICP
10
ICN
SCF 18
16
VAP
REFIN/OUT 12
15
VBP
SAME AS VAP
14
VCP
13
VN
TO
FREQUENCY
COUNTER
K8
10MHz
7
SAME AS VAP
33nF
2
CLKOUT 20
CLKIN 19
S0 21
S1
22pF
22
REVP 4
1kΩ
4
820Ω
22pF
33nF
SAME AS
IAP, IAN
1
F2 23
CF 1
6
K7
ABS F1 24
IAP
33nF
1kΩ
17
VDD
1kΩ
0.1µF
VDD
10µF
AGND DGND
11
2
Figure 10. Test Circuit for Performance Curves
Rev. 0 | Page 10 of 24
05905-015
10µF
ILOAD
ADE7752B
THEORY OF OPERATION
The low frequency output of the ADE7752B is generated by
accumulating the total active power information. This low
frequency inherently means a long accumulation time between
output pulses. The output frequency is therefore proportional to
the average active power. This average active power information
can, in turn, be accumulated (for example, by a counter) to
generate active energy information. Because of its high output
frequency and, therefore, shorter integration time, the CF
output is proportional to the instantaneous active power. This
pulse is useful for system calibration purposes that take place
under steady load conditions.
The six signals from the current and voltage transducers are
digitized with ADCs. These ADCs are 16-bit, second-order
∑-Δ with an oversampling rate of 833 kHz. This analog input
structure greatly simplifies transducer interface by providing a
wide dynamic range and bipolar input for direct connection to
the transducer. High-pass filters in the current channels remove
the dc component from the current signals. This eliminates any
inaccuracies in the active power calculation due to offsets in the
voltage or current signals (see the HPF and Offset Effects section).
The active 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 of each
phase. To extract the active power component, the dc component, the instantaneous power signal is low-pass filtered on
each phase. Figure 11 illustrates the instantaneous active power
signal and shows how the active power information can be
extracted by low-pass filtering the instantaneous power signal.
This method is used to extract the active power information
on each phase of the polyphase system. The total active power
information is then obtained by adding the individual phase
active power. This scheme correctly calculates active power
for nonsinusoidal 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.
POWER FACTOR CONSIDERATIONS
Low-pass filtering, the method used to extract the active power
information from the individual instantaneous power signal, is
still valid when the voltage and current signals of each phase are
not in phase. Figure 12 displays the unity power factor condition and a displacement power factor (DPF) = 0.5, that is,
current signal lagging the voltage by 60°, for one phase of the
polyphase. Assuming that the voltage and current waveforms
are sinusoidal, the active power component of the instantaneous
power signal (the dc term) is given by
⎛ V × 1 ⎞ × cos(60°)
⎜
⎟
⎝ 2 ⎠
(2)
This is the correct active power calculation.
p(t) = i(t) × v(t)
WHERE:
v(t) = V × cos (ωt)
i(t) = I × cos (ωt)
p(t) = V × I
{1+ cos (2ωt)}
2
V×I
V×I
2
TIME
V×I
2
INSTANTANEOUS
POWER SIGNAL - p(t)
INSTANTANEOUS
VA × IA + VB × IB +
ACTIVE POWER SIGNAL
VC × IC
2
HPF
IAP
IAN
ADC
ABS
LPF
|X|
MULTIPLIER
VAP
ADC
DIGITAL-TO-FREQUENCY
F1
F2
HPF
IBP
IBN
ADC
LPF
|X|
MULTIPLIER
VBP
INSTANTANEOUS
TOTAL POWER
SIGNAL
DIGITAL-TO-FREQUENCY
ADC
CF
HPF
ADC
MULTIPLIER
VCP
VN
LPF
|X|
05905-016
ICP
ICN
ADC
Figure 11. Signal Processing Block Diagram
Rev. 0 | Page 11 of 24
ADE7752B
INSTANTANEOUS
POWER SIGNAL
i (t ) = I O + 2 × ∑ In × sin (nωt βn )
∞
INSTANTANEOUS
ACTIVE POWER SIGNAL
(4)
n =1
where:
i(t) is the instantaneous current.
IO is the dc component.
In is the rms value of current harmonic n.
βn is the phase angle of the current harmonic.
V× I
2
0V
CURRENT
VOLTAGE
INSTANTANEOUS
POWER SIGNAL
Using Equation 3 and Equation 4, the active power, P, can be
expressed in terms of its fundamental active power (P1) and
harmonic active power (PH).
INSTANTANEOUS
ACTIVE POWER SIGNAL
P = P 1 + PH
V× I
× cos(60°)
2
where:
0V
P1 = V 1 × I1 cos φ1
60°
05905-017
VOLTAGE
φ1 = α1 − β1
CURRENT
∞
PH = ∑ Vn × I n cos φn
Figure 12. DC Component of Instantaneous Power Signal
n =1
NONSINUSOIDAL VOLTAGE AND CURRENT
∞
n =0
where:
v(t) is the instantaneous voltage.
VO is the average value.
Vn is the rms value of voltage harmonic n.
α n is the phase angle of the voltage harmonic.
(6)
φn = αn − βn
The active power calculation method also holds true for nonsinusoidal current and voltage waveforms. All voltage and
current waveforms in practical applications have some
harmonic content. Using the Fourier transform, instantaneous
voltage and current waveforms can be expressed in terms of
their harmonic content
v(t ) = VO + 2 × ∑ Vn × sin(nωt + α n )
(5)
(3)
As can be seen from Equation 6, a harmonic active power
component is generated for every harmonic, provided that
harmonic is present in both the voltage and current waveforms.
The power factor calculation has been shown to be accurate in
the case of a pure sinusoid. Therefore, the harmonic active
power also correctly accounts for power factor because harmonics
are made up of a series of pure sinusoids. A limiting factor on
harmonic measurement is the bandwidth. On the ADE7752B,
the bandwidth of the active power measurement is 14 kHz with
a master clock frequency of 10 MHz.
Rev. 0 | Page 12 of 24
ADE7752B
ANALOG INPUTS
CURRENT CHANNELS
VOLTAGE CHANNELS
The voltage outputs from the current transducers are connected
to the ADE7752B current channels, which are fully differential
voltage inputs. IAP, IBP, and ICP are the positive inputs for IAN,
IBN, and ICN, respectively.
The output of the line voltage transducer is connected to the
voltage inputs of the ADE7752B. Voltage channels are pseudodifferential voltage inputs. VAP, VBP, and VCP are the positive
inputs with respect to VN.
The maximum peak differential signal on the current channel
should be less than ±500 mV (353 mV rms for a pure sinusoidal
signal) for the specified operation.
The maximum peak differential signal on the voltage channel is
±500 mV (353 mV rms for a pure sinusoidal signal) for specified operation.
Figure 14 illustrates the maximum signal levels that can be
connected to the ADE7752B voltage channels.
IAP–IAN
+500mV
VAP–VN
IAP
DIFFERENTIAL INPUT
±500mV MAX PEAK
IA
+500mV
IAN
VAP
VCM
AGND
Figure 13. Maximum Signal Levels, Current Channel
The maximum signal levels on IAP and IAN are shown in
Figure 13. The maximum differential voltage between IAP
and IAN is ±500 mV. The differential voltage signal on the
inputs must be referenced to a common mode, for example,
AGND. The maximum common-mode signal shown in
Figure 13 is ±25 mV.
DIFFERENTIAL INPUT
±500mV MAX PEAK
VA
VN
VCM
COMMON-MODE
±25mV MAX
–500mV
VCM
AGND
05905-019
–500mV
VCM
05905-018
COMMON-MODE
±25mV MAX
Figure 14. Maximum Signal Levels, Voltage Channel
Voltage channels must be driven from a common-mode voltage,
that is, the differential voltage signal on the input must be referenced to a common mode (usually AGND). The analog inputs
of the ADE7752B 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.
Rev. 0 | Page 13 of 24
ADE7752B
TYPICAL CONNECTION DIAGRAMS
CURRENT CHANNEL CONNECTION
METER CONNECTIONS
Figure 15 shows a typical connection diagram for the current
channel (IA). A current transformer (CT) is the current transducer selected for this example. Notice that the common-mode
voltage for the current channel is AGND and is derived by
center-tapping the burden resistor to AGND. This provides the
complementary analog input signals for IAP and IAN. The CT
turns ratio and burden resistor Rb are selected to give a peak
differential voltage of ±500 mV at maximum load.
In 3-phase service, two main power distribution services exist:
3-phase, 4-wire or 3-phase, 3-wire. The additional wire in the
3-phase, 4-wire arrangement is the neutral wire. The voltage
lines have a phase difference of ±120° (±2π/3 radians) between
each other (see Equation 7).
In theory, it is better to center tap Rb; however, this requires
very careful attention to the layout and matching of the resistors
to ensure that the channels have the same resistance. A single
resistor may be more practical and is a valid design choice.
Rf
Rb
±500mV
Rf
IP
Cf
2π ⎞
VB (t ) = 2 × VB × cos ⎛⎜ ωlt +
⎟
3 ⎠
⎝
IAP
where VA, VB, and VC represent the voltage rms values of the
different phases.
IAN
The current inputs are represented by
Cf
PHASE NEUTRAL
I A (t ) = 2 I A × cos (ωlt + φ A )
2π
I B (t ) = 2 I B × cos ⎛⎜ ωlt +
+ φ B ⎞⎟
3
⎠
⎝
Figure 15. Typical Connection for Current Channels
Rf
PT
Cf
±500mV
where:
IA, IB, and IC represent the rms value of the current of each phase.
φA, φB, and φC represent the phase difference of the current and
voltage channel of each phase.
The instantaneous powers can then be calculated as follows:
PA(t) = VA(t) × IA(t)
PB(t) = VB(t) × IB(t)
PC(t) = VC(t) × IC(t)
Then:
VAP
PA (t ) = V A × I A × cos(φ A ) − V A × I A × cos (2ωl t + φ A )
VN
PB (t ) =
Rf
AGND
4π
+ φ B ⎞⎟
V B × I B × cos(φ B ) − V B × I B × cos ⎛⎜ 2ω l t +
3
⎝
⎠
Cf
PHASE NEUTRAL
Rb*
VAP
±500mV
VN
Rf
Cf
PHASE NEUTRAL
*Ra >> Rf + VR; *Rb + VR = Rf
Figure 16. Typical Connections for Voltage Channels
05905-021
VR*
(9)
8π
PC (t ) = VC × I C × cos(φ C ) − VC × I C × cos ⎛⎜ 2ωl t +
+ φ C ⎞⎟
3
⎝
⎠
Cf
Ra*
(8)
4π
I C (t ) = 2 I C × cos ⎛⎜ ωlt +
+ φC ⎞⎟
3
⎠
⎝
VOLTAGE CHANNEL CONNECTION
Figure 16 shows two typical connections for the voltage channel.
The first option uses a potential transformer (PT) to provide
complete isolation from the main voltage. In the second option,
the ADE7752B is biased around the neutral wire, and a resistor
divider is used to provide a voltage signal proportional to the
line voltage. Adjusting the ratio of Ra, Rb, and VR is a convenient
way of carrying out a gain calibration on the meter. VR can be
implemented using either a potentiometer or a binary weighted
series of resistors. Either configuration works, however, the
potentiometer is subject to noise over time. Two fixed value
resistors can be used in place of VR to minimize the noise.
(7)
4π ⎞
V C (t ) = 2 × VC × cos ⎛⎜ ωlt +
⎟
3 ⎠
⎝
05905-020
CT
VA (t ) = 2 × VA × cos (ωlt )
As shown in Equation 9, the active power calculation per phase
is made when current and voltage inputs of one phase are
connected to the same channel (A, B, or C). Then the
summation of each individual active power calculation gives the
total active power information, P(t) = PA(t) + PB(t) + PC(t).
Rev. 0 | Page 14 of 24
ADE7752B
Figure 18 shows the connections of the ADE7752B analog
inputs with the power lines in a 3-phase, 4-wire Wye service.
Figure 17 shows the connections of the ADE7752B analog
inputs with the power lines in a 3-phase, 3-wire delta service.
Ra*
Cf
Ra*
Rb*
Rb*
VR*
VR*
VAP
Cf
VAP
IAP
IAP
ANTIALIASING
FILTERS
CT
IAN
Rb*
IAN
Rb*
ANTIALIASING
FILTERS
CT
CT
PHASE A
PHASE A
PHASE C
SOURCE
SOURCE
Rf
VN
Cf
PHASE C
Rb*
ANTIALIASING
FILTERS
IBP
IBN
VBP
VR*
Rb*
ANTIALIASING
FILTERS
Ra*
IBP
IBN
Rb*
VBP
VR*
*Ra >> Rf + VR; *Rb + VR = Rf
Cf
Rb*
ANTIALIASING
FILTERS
Rb*
LOAD
ICN
VCP
VR*
Rf
ICP
VN
CF
Figure 17. 3-Phase, 3-Wire Meter Connection with ADE7752B
*Ra >> Rf + VR; *Rb + VR = Rf
Note that only two current inputs and two voltage inputs of the
ADE7752B are used in this case. The active power calculated by
the ADE7752B does not depend on the selected channels.
Rev. 0 | Page 15 of 24
Figure 18. 3-Phase, 4-Wire Meter Connection with ADE7752B
05905-023
Cf
Cf
CT
05905-022
Ra*
Ra*
Rb*
LOAD
CT
PHASE B
PHASE B
ADE7752B
POWER SUPPLY MONITOR
VDD
5V
4V
VREF
2.4V
1.9V
0V
INTERNAL
INACTIVE
RESET
The power supply and decoupling for the part should be such
that the ripple at VDD does not exceed ±5% as specified for
normal operation.
Rev. 0 | Page 16 of 24
ACTIVE
INACTIVE
Figure 19. On-Chip Power Supply Monitor
05905-024
The ADE7752B contains an on-chip power supply monitor. The
power supply (VDD) is monitored continuously. At power-up,
when the supply is less than 4 V ± 2% and VREF is less than 1.9 V
(typical), the outputs of the ADE7752B are inactive and the data
path is held in reset. Once VDD is greater than 4 V ± 2% and
VREF is greater than 1.9 V (typical), the chip is active and energy
accumulation begins. At power-down, when VDD falls below 4 V
or VREF falls below 1.9 V (typical), the data path is again held in
reset. This implementation ensures correct device operation at
power-up and at power-down. The power supply monitor has
built-in hysteresis and filtering. This gives a high degree of
immunity to false triggering due to noisy supplies.
ADE7752B
HPF AND OFFSET EFFECTS
The ADE7752B is phase compensated up to 1 kHz as shown. This
ensures correct active harmonic power calculation even at low
power factors.
0.07
0.06
0.05
PHASE (Degrees)
Figure 20 shows the effect of offsets on the active power
calculation. An offset on the current channel and the voltage
channel contributes a dc component after multiplication, as
shown in Figure 20. Because this dc component is extracted by
the LPF and is used to generate the active power information
for each phase, the offsets can contribute a constant error to the
total active power calculation. The HPF in the current channels
avoids this problem easily. By removing the offset from at least
one channel, no error component can be generated at dc by the
multiplication. Error terms at cos(ωt) are removed by the LPF
and the digital-to-frequency conversion (see the Digital-toFrequency Conversion section).
{V cos(ωt ) + VOS }× {I cos(ωt ) + IOS } =
+
2
0.02
0.01
0
+ VOS × IOS + VOS × I cos(ωt ) + I OS × V cos(ωt ) (10)
2
V×I
0.03
–0.01
× cos(2ωt )
05905-031
V×I
0.04
0
100
200
300
400 500 600 700
FREQUENCY (Hz)
800
900 1000
Figure 21. Phase Error Between Channels (0 Hz to 1 kHz)
0.010
DC COMPONENT (INCLUDING ERROR TERM)
IS EXTRACTED BY THE LPF FOR REAL
POWER CALCULATION
VOS × IOS
0.008
V× I
2
PHASE (Degrees)
0.006
IOS × V
VOS × I
0.002
0
2ω
FREQUENCY (RAD/sec)
–0.002
05905-032
ω
05905-026
0
0.004
Figure 20. Effect of Channel Offset on the Active Power Calculation
The HPF in the current channels has an associated phase response
that is compensated for on-chip. Figure 21 and Figure 22 show the
phase error between channels with the compensation network.
Rev. 0 | Page 17 of 24
–0.004
40
45
50
55
60
FREQUENCY (Hz)
65
Figure 22. Phase Error Between Channels (40 Hz to 70 Hz)
70
ADE7752B
DIGITAL-TO-FREQUENCY CONVERSION
After multiplication, the digital output of the low-pass filter
contains the active power information of each phase. However,
because this LPF is not an ideal brick wall filter implementation,
the output signal also contains attenuated components at the line
frequency and its harmonics, that is, cos(hωt), where h = 1, 2, 3 …
The average value of a sinusoidal signal is zero. Thus, the
frequency generated by the ADE7752B is proportional to the
average active power. Figure 23 shows the digital-to-frequency
conversion for steady load conditions, that is, constant voltage
and current.
The magnitude response of the filter is given by
The frequency output CF varies over time, even under steady load
conditions (see Figure 23). This frequency variation is primarily
due to the cos(2ωt) components in the instantaneous active power
signal. The output frequency on CF can be up to 160× higher than
the frequency on F1 and F2. The higher output frequency is
generated by accumulating the instantaneous active power signal
over a much shorter time, while converting it to a frequency. This
shorter accumulation period means less averaging of the cos(2ωt)
component. Therefore, some of this instantaneous power signal
passes through the digital-to-frequency conversion.
1
⎧f⎫
1+ ⎨ ⎬
⎩8⎭
(11)
2
where the −3 dB cutoff frequency of the low-pass filter is 8 Hz.
For a line frequency of 50 Hz, this gives an attenuation of the 2ω
(100 Hz) component of approximately −22 dB. The dominating
harmonic is twice the line frequency, that is, cos(2ωt), due to
the instantaneous power signal. Figure 23 shows the instantaneous active power signal at the output of the CF, which still contains
a significant amount of instantaneous power information,
cos(2ωt).
Where CF is used for calibration purposes, the frequency counter
should average the frequency to remove the ripple and obtain a
stable frequency. If CF is being used to measure energy, for
example, in a microprocessor-based application, the CF output
should also be averaged to calculate power. Because the outputs F1
and F2 operate at a much lower frequency, significant averaging of
the instantaneous active power signal is carried out. The result is a
greatly attenuated sinusoidal content and a virtually ripple-free
frequency output on F1 and F2, which are used to measure energy
in a stepper motor-based meter.
This signal is then passed to the digital-to-frequency converter
where it is integrated (accumulated) over time to produce an
output frequency. This accumulation of the signal suppresses or
averages out any nondc component in the instantaneous active
power signal.
ABS
VA
LPF
|X|
F1
IA
DIGITAL-TOFREQUENCY
F1
F2
VB
LPF
|X|
IB
CF
VC
TIME
CF
DIGITAL-TOFREQUENCY
TIME
LPF
MULTIPLIER
IC
|X|
V×I
2
LPF TO EXTRACT
REAL POWER
(DC TERM)
cos(2ωt)
ATTENUATED BY LPF
0
2ω
ω
FREQUENCY (RAD/sec)
INSTANTANEOUS REAL POWER SIGNAL
(FREQUENCY DOMAIN)
Figure 23. Active Power-to-Frequency Conversion
Rev. 0 | Page 18 of 24
05905-029
MULTIPLIER
FREQUENCY
MULTIPLIER
FREQUENCY
|H ( f )| =
ADE7752B
ACCUMULATION OF 3-PHASE POWER
Power Measurement Considerations
Calculating and displaying power information always have some
associated ripple that depends on the integration period used in the
MCU to determine average power as well as the load. For example,
at light loads, the output frequency can be 10 Hz. With an integration period of 2 seconds, only about 20 pulses are counted. The
possibility of missing one pulse always exists because the
ADE7752B output frequency is running asynchronously to the
MCU timer. This results in a 1-in-20 or 5% error in the power
measurement. To remedy this, an appropriate integration time
should be considered to achieve the desired accuracy.
Mode Selection of the Sum of the Three Active Energies
The ADE7752B can be configured to execute the arithmetic
sum of the three active energies, Wh = WhΦA + WhΦB + WhΦC,
or the sum of the absolute value of these energies, Wh = |WhΦA|
+ |WhΦB| + |WhΦC|. The selection between the two modes can
be made by setting the ABS pin. Logic high and logic low
applied on the ABS pin correspond to the arithmetic sum and
the sum of absolute values, respectively.
When the sum of the absolute values is selected, the active
energy from each phase is always counted positive in the total
active energy. It is particularly useful in 3-phase, 4-wire installa-
tion where the sign of the active power should always be the
same. If the meter is misconnected to the power lines, that is, if
CT is connected in the wrong direction, the total active energy
recorded without this solution can be reduced by two-thirds.
The sum of the absolute values assures that the active energy
recorded represents the actual active energy delivered. In this
mode, the reverse power pin still detects when the arithmetic
sum of the active powers is negative, but energy continues to
accumulate regardless of the sign.
Negative Total Power Detection
The ADE7752B detects when total power, calculated as the
arithmetic sum of the three phases, is negative. This detection
is independent of the mode of sum of the three powers (arithmetic
or absolute). This mechanism can detect an incorrect connection of the meter or generation of negative active energy. When
the sum of the powers of the three phases is negative, the REVP
pin output goes active high. When the sum of the powers of the
three phases is positive, the REVP pin output is reset to low.
The REVP pin output changes state at the same time as a pulse
is issued on CF. If the sum of the powers of the three phases is
negative, then the REVP pin output stays high until the sum is
positive or all three phases are below the no-load threshold.
Rev. 0 | Page 19 of 24
ADE7752B
TRANSFER FUNCTION
FREQUENCY OUTPUTS F1 AND F2
Example 1
The ADE7752B calculates the product of six voltage signals
(on current channel and voltage channel) and then low-pass
filters this product to extract active power information. This
active power information is then converted to a frequency.
The frequency information is output on F1 and F2 in the form
of active high pulses. The pulse rate at these outputs is relatively
low, for example, 2.09 Hz maximum for ac signals with SCF =
S0 = 0; S1 = 1 (see Table 6). This means that the frequency at
these outputs is generated from active power information
accumulated over a relatively long period. The result is an
output frequency that is proportional to the average active
power. The averaging of the active 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:
In this example, with ac voltages of ±500 mV peak applied to
the voltage channels and current channels, the expected output
frequency is calculated as follows:
Freq =
6.181 × (V AN × I A + VBN × I B + VCN × I C ) × f 1 to 7
VREF 2
where:
Freq is the output frequency on F1 and F2 (Hz).
VAN, VBN, and VCN are the differential rms voltage signals on
voltage channels (V).
IA, IB, and IC are the differential rms voltage signals on current
channels (V).
VREF is the reference voltage (2.4 V ± 8%) (V).
f1 to 7 is one of seven possible frequencies selected by using the
logic inputs SCF, S0, and S1 (see Table 5).
(12)
f 1to 7 = 0.56 Hz, SCF = S0 = S1 = 1
V AN = V BN = VCN = IA = IB = IC
VREF
1
S1
0
S0
0
f1 to 7 (Hz)
2.24
1
0
0
4.49
0
0
1
1.12
1
0
1
4.49
0
1
0
5.09
1
1
0
1.12
0
1
1
0.56
1
1
1
0.56
(13)
Note that if the on-chip reference is used, actual output frequencies can vary from device to device due to reference
tolerance of ±8%.
Freq = 3 ×
6.313 × 0.5 × 0.5 × 0.58
2 × 2 × 2. 4 2
= 0.230 Hz
(14)
As can be seen from these two example calculations, the maximum
output frequency for ac inputs is always half of that for dc input
signals. The maximum frequency also depends on the number
of phases connected to the ADE7752B. In a 3-phase, 3-wire delta
service, the maximum output frequency is different from the maximum output frequency in a 3-phase, 4-wire Wye service. The
reason is that there are only two phases connected to the analog
inputs, but also that in a delta service, the current channel input
and voltage channel input of the same phase are not in phase in
normal operation.
Table 5. f1 to 7 Frequency Selection1
SCF
0
0.5
V rms
2
= 2.4 V (nominal reference value )
= 500 mV peak ac =
f1 to 7 is a fraction of the master clock and therefore varies if the specified
CLKIN frequency is altered.
Rev. 0 | Page 20 of 24
ADE7752B
Example 2
f 1to 7 = 0.56 Hz, SCF = S0 = S1 = 1
In this example, the ADE7752B is connected to a 3-phase,
3-wire delta service as shown in Figure 17. The total active
energy calculation processed in the ADE7752B can be
expressed as
V AN = V BN = I A = I B = I C = 500 mV peak ac =
VCN
Total Active Power = (VA – VC) × IA + (VB – VC) × IB
With respect to the voltage and current inputs in Equation 7
and Equation 8, the total active power (P) is
(I
AP
4π ⎞ ⎞
⎛
P = ⎜ 2 × V A × cos (ωl t ) − 2 × VC × cos⎛⎜ ω l t +
⎟⎟ ×
3 ⎠⎠
⎝
⎝
2 × I A × cos (ω l t ) +
For simplification, assume that ΦA = ΦB = ΦC = 0 and
VA = VB = VC = V. The preceding equation becomes
(16)
(17)
where:
VAN = V × sin(2π/3)
VBN = V × sin(π/3)
As the LPF on each channel eliminates the 2ωl component of
the equation, the active power measured by the ADE7752B is
P = V AN
6.313 × 0.5 × 0.5 × 0.56
3
×
= 0.133 Hz
2 × 2 × 2.4 2
2
(20)
SCF
0
1
0
1
0
1
0
1
S1
0
0
0
0
1
1
1
1
S0
0
1
1
1
0
0
1
1
Maximum Frequency for AC Inputs (Hz)
0.92
1.84
0.46
1.84
2.09
0.46
0.23
0.23
FREQUENCY OUTPUT CF
P then becomes
3
3
×IA ×
+ V BN × I B ×
2
2
Freq = 2 ×
Table 6. Maximum Output Frequency on F1 and F2
2π ⎞
4π ⎞ ⎞
⎛
⎛
⎛
⎜ 2 × V B × cos⎜ ωl t +
⎟ − v 2 × VC × cos⎜ ωl t +
⎟⎟ ×
3 ⎠
3 ⎠⎠
⎝
⎝
⎝
2π ⎞
2 × I B × cos⎛⎜ ωl t +
⎟
3 ⎠
⎝
(15)
2π
2π ⎞ ⎞
⎛
P = V AN × I A × ⎜ sin⎛⎜ ⎞⎟ + sin⎛⎜ 2ωl t +
⎟⎟ +
3 ⎠⎠
⎝
⎝ ⎝ 3 ⎠
π
π ⎞
⎛
V BN × I B × ⎜ sin⎛⎜ ⎞⎟ + sin⎛⎜ 2ωl t + ⎞⎟ ⎟
3 ⎠⎠
⎝
⎝ ⎝3⎠
Note that if the on-chip reference is used, actual output
frequencies can vary from device to device due to a reference
tolerance of ±8%.
Table 6 shows a complete listing of all maximum output
frequencies when using all three channel inputs.
− I AN ) + (VB − VC )× (I BP − I BN )
2π
2π
P = 2 × V × I A × sin⎛⎜ ⎞⎟ × sin⎛⎜ ω l t + ⎞⎟ × cos(ωl t ) +
3 ⎠
⎝
⎝ 3 ⎠
π
2π
2 × V × I B × sin⎛⎜ ⎞⎟ × sin(ω l t + π) × cos⎛⎜ ω l t + ⎞⎟
3 ⎠
⎝
⎝3⎠
(19)
VREF = 2.4 V nominal reference value
where:
VA, VB, and VC represent the voltage on Phase A, Phase B, and
Phase C, respectively.
IA and IB represent the current on Phase A and Phase B,
respectively.
P = (V A − VC )
0.5
V rms
2
= IC = 0
(18)
If full-scale ac voltage of ±500 mV peak is applied to the voltage
channels and current channels, the expected output frequency
is calculated as follows:
The pulse output calibration frequency (CF) is intended for use
during calibration. The output pulse rate on CF can be up to
64× the pulse rate on F1 and F2. Table 7 shows how the two
frequencies are related, depending on the states of the logic
inputs S0, S1, and SCF. Because of its relatively high pulse rate,
the frequency at this logic output is proportional to the instantaneous active power. As is the case with F1 and F2, the frequency is
derived from the output of the low-pass filter after multiplication.
However, because the output frequency is high, this active
power information is accumulated over a much shorter time.
Thus, less averaging is carried out in the digital-to-frequency
conversion. The CF output is much more responsive to power
fluctuations with much less averaging of the active power signal
(see Figure 11).
Table 7. Maximum Output Frequency on CF
SCF
0
1
0
1
0
1
0
1
Rev. 0 | Page 21 of 24
S1
0
0
0
0
1
1
1
1
S0
0
0
1
1
0
0
1
1
f1 to 7 (Hz)
2.24
4.49
1.12
4.49
5.09
1.12
0.56
0.56
CF Maximum for AC Signals (Hz)
16 × F1, F2 = 14.76
8 × F1, F2 = 14.76
32 × F1, F2 = 14.76
16 × F1, F2 = 29.51
160 × F1, F2 = 334
16 × F1, F2 = 7.38
32 × F1, F2 = 7.38
16 × F1, F2 = 3.69
ADE7752B
SELECTING A FREQUENCY FOR AN ENERGY METER APPLICATION
As shown in Table 5, the user can select one of seven frequencies.
This frequency selection determines the maximum frequency
on F1 and F2. These outputs are intended to be used to drive
the energy register (electromechanical or other). Because seven
different output frequencies can be selected, the available
frequency selection has been optimized for a 3-phase, 4-wire
service with a meter constant of 100 imp/kWhr and a maximum current of between 10 A and 100 A. Table 8 shows the
output frequency for several maximum currents (IMAX) with a
line voltage of 220 V (phase neutral). In all cases, the meter
constant is 100 imp/kWhr.
When selecting a suitable f1 to 7 frequency for a meter design, the
frequency output at IMAX (maximum load) with a 100 imp/kWhr
meter constant should be compared with Column 5 of Table 9.
The frequency that is closest in Table 9 determines the best
choice of frequency (f1 to 7). For example, if a 3-phase, 4-wire
Wye meter with a 25 A maximum current is being designed,
the output frequency on F1 and F2 with a 100 imp/kWhr meter
constant is 0.46 Hz at 25 A and 220 V (see Table 8). Looking at
Table 9, the closest frequency to 0.46 Hz in Column 5 is 0.46 Hz.
Therefore, f1 to 7 = 4.49 Hz is selected for this design.
Table 8. F1 and F2 Frequency at 100 imp/kWhr
Figure 2 shows a timing diagram for the various frequency
outputs. 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 alternating high going pulses. The pulse width (t1) is set at
120 ms, and the time between the rising edges of F1 and F2 (t3)
is approximately half the period of F1 (t2). If, however, the
period of F1 and F2 falls below 550 ms (1.81 Hz), the pulse
width of F1 and F2 is set to half of their period. The maximum
output frequencies for F1 and F2 are shown in Table 6.
IMAX (A)
10
25
40
60
80
100
F1 and F2 (Hz)
0.18
0.46
0.73
1.10
1.47
1.83
The f1 to 7 frequencies allow complete coverage of this range of
output frequencies on F1 and F2. When designing an energy
meter, the nominal design voltage on the voltage channels
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 allows overcurrent
signals and signals with high crest factors to be accommodated.
Table 9 shows the output frequency on F1 and F2 when all six
analog inputs are half scale.
FREQUENCY OUTPUTS
The high frequency CF output is intended to be used for
communications and calibration purposes. CF produces a
90 ms-wide active high pulse (t4) at a frequency proportional
to active power. The CF output frequencies are given in Table 7.
As in the case of F1 and F2, if the period of CF (t5) falls below
190 ms, the 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.
Table 9. F1 and F2 Frequency with Half-Scale AC Inputs
SCF
0
1
0
1
0
1
0
1
S1
0
0
0
0
1
1
1
1
S0
0
0
1
1
0
0
1
1
f1 to 7 (Hz)
2.24
4.49
1.12
4.49
5.09
1.12
0.56
0.56
Frequency on F1 and F2
(Half-Scale AC Inputs) (Hz)
0.23
0.46
0.12
0.46
0.52
0.12
0.06
0.06
Rev. 0 | Page 22 of 24
ADE7752B
NO-LOAD THRESHOLD
The ADE7752B includes an innovative no-load threshold detection
scheme that detects if a current input, when multiplied with any
of the three voltages inputs, cannot create power larger than a noload threshold. This threshold represents 0.0075% of the fullscale output frequency.
For example, if the A, B and C voltage phases are 50% of fullscale input and 120° apart, and Current Phase A is 10% of full
scale with a PF = 0, this detection scheme detects that VA × IA is
below the no-load threshold but that VB × IA and VC × IA are not.
Therefore, the ADE7752B does not detect a no-load threshold
for VA × IA and lets this phase contribute to the total power.
However, in the same voltage conditions, if current Phase A is
0.0075% of full scale with a PF = 1, this detection scheme detects
that VA × IA is below the no-load threshold and because VB × IA
and VC × IA are as well, VA × IA is detected as below the no-load
threshold and its contribution to the total power is stopped.
The no-load threshold is given as 0.0075% of the full-scale output
frequency for each of the f1 to 7 frequencies (see Table 10). For
example, for an energy meter with a 100 imp/kWhr meter
constant using f1 to 7 (4.49 Hz), the minimum output frequency
at F1 or F2 is 1.38 × 10−4 Hz. This is 2.21 × 10−3 Hz at CF
(16 × F1 Hz). In this example, the no-load threshold is equivalent to 4.8 W of load, or a start-up current of 20.7 mA at 240 V.
Table 10. CF, F1, and F2 Minimum Frequency at No-Load
Threshold
SCF
0
1
0
1
0
1
0
1
Rev. 0 | Page 23 of 24
S1
0
0
0
0
1
1
1
1
S0
0
0
1
1
0
0
1
1
F1, F2 Minimum (Hz)
6.92E − 05
1.38E − 04
3.46E − 05
1.38E − 04
1.57E − 04
3.46E − 05
1.73E − 05
1.753 − 05
CF Minimum (Hz)
1.11E − 03
1.11E − 03
1.11E − 03
2.21E − 03
2.51E − 02
5.53E − 04
5.53E − 04
2.77E − 04
ADE7752B
OUTLINE DIMENSIONS
15.60 (0.6142)
15.20 (0.5984)
13
24
7.60 (0.2992)
7.40 (0.2913)
12
2.65 (0.1043)
2.35 (0.0925)
0.30 (0.0118)
0.10 (0.0039)
COPLANARITY
0.10
10.65 (0.4193)
10.00 (0.3937)
1.27 (0.0500)
BSC
0.51 (0.0201)
0.31 (0.0122)
SEATING
PLANE
0.75 (0.0295)
0.25 (0.0098)
45°
8°
0°
0.33 (0.0130)
0.20 (0.0079)
1.27 (0.0500)
0.40 (0.0157)
COMPLIANT TO JEDEC STANDARDS MS-013-AD
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.
060706-A
1
Figure 24. 24-Lead Standard Small Outline Package [SOIC_W]
Wide Body
(RW-24)
Dimensions shown in millimeters and (inches)
ORDERING GUIDE
Model
ADE7752BARWZ1
ADE7752BARWZ-RL1
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
Package Description
24-Lead Standard Small Outline Package [SOIC_W]
24-Lead [SOIC_W], on 13” Reel
Z = RoHS Compliant Part.
©2007 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D05905-0-8/07(0)
Rev. 0 | Page 24 of 24
Package Option
RW-24
RW-24
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