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PDF ADE7757 Data sheet ( Hoja de datos )
| Número de pieza | ADE7757 | |
| Descripción | Energy Metering IC with Integrated Oscillator | |
| Fabricantes | Analog Devices | |
| Logotipo |  |
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PRELIMINARY TECHNICAL DATA
a
Energy Metering IC
with Integrated Oscillator
Preliminary Technical Data
ADE7757*
FEATURES
On Chip Oscillator as clock source
High Accuracy, Supports 50 Hz/60 Hz IEC 521/1036
Less than 0.1% Error Over a Dynamic Range of
500 to 1
The ADE7757 Supplies Average Real Power on the
Frequency Outputs F1 and F2
The High Frequency Output CF Is Intended for
Calibration and Supplies Instantaneous Real Power
Direct Drive for Electromechanical Counters and
Two 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 2.5 V ؎ 8% (30 ppm/؇C Typical)
with External Overdrive Capability
Single 5 V Supply, Low Power (15 mW Typical)
Low Cost CMOS Process
AC Input only
GENERAL DESCRIPTION
The ADE7757 is a high accuracy electrical energy mea-
surement IC. It is a pin reduction version of AD7755
with an enhancement of a precise oscillator circuit that
serves as a clock source to the chip. The ADE7757
eliminates the cost of an external crystal or resonator,
thus reducing the overall cost of a meter built with this
IC. The chip directly interfaces with shunt resistor and
only operates with AC input.
The ADE7757 specifications surpass the accuracy require-
ments as quoted in the IEC1036 standard. Due to the
similarity between the ADE7757 and AD7755, the Appli-
cation Note AN-559 can be used as a basis for a descrip-
tion of an IEC1036 low cost watt-hour meter reference
design.
The only analog circuitry used in the ADE7757 is in the
sigma-delta ADCs and reference circuit. All other signal
processing (e.g., multiplication and filtering) is carried
out in the digital domain. This approach provides superior
stability and accuracy over time and extreme environmen-
tal conditions.
The ADE7757 supplies average real power information on
the low frequency outputs F1 and F2. These outputs may
be used to directly drive an electromechanical counter or
interface with an MCU. The high frequency CF logic
output, ideal for calibration purposes, provides instanta-
neous real power information.
The ADE7757 includes a power supply monitoring circuit
on the VDD supply pin. The ADE7757 will remain in reset
mode until the supply voltage on VDD reaches approxi-
mately 4 V. If the supply falls below 4 V, the ADE7757
will also reset and the F1, F2 and CF outputs will be in
their non-active modes.
Internal phase matching circuitry ensures that the voltage
and current channels are phase matched while the HPF in
the current channel eliminates dc offsets. An internal no-
load threshold ensures that the ADE7757 does not exhibit
creep when no load is present.
The ADE7757 is available in 16-lead SOIC narrow-body
package.
FUNCTIONAL BLOCK DIAGRAM
VDD AGND
DGND
V2P
V2N
V1N
V1P
POWER
SUPPLY MONITOR
ADE7757
∑ ∆ ...110101...
ADC
MULTIPLIER
SIGNAL
PROCESSING
BLOCK
LPF
∑∆
ADC
PHASE
CORRECTION HPF
. . .11011001. . .
Φ
2.5V 4kV
REFERENCE
INTERNAL
OSCILLATOR
DIGITAL-TO-FREQUENCY
CONVERTER
REFIN/OUT RCLKIN RESERVED SCF S0 S1
*U.S. Patents 5,745,323, 5,760,617, 5,862,069, 5,872,469; other pending.
CF F1 F2
REV. PrC.
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
which may result from its use. No license is granted by implication or
otherwise under any patent or patent rights of Analog Devices.
One Technology Way, P.O. Box 9106, Norwood, MA 02062-9106, USA.
Tel: 781/329-4700 World Wide Web Site: http://www.analog.com
Fax: 781/326-8703
© Analog Devices, Inc., February 2002
1 page  
PRELIMINARY TECHNICAL DATA
ADE7757
Pin No.
1
2,3
4, 5
6
7
8
9,10
11
12
13
14
15,16
Mnemonic
VDD
V2P, V2N
V1N, V1P
AGND
REFIN/OUT
SCF
S1, S0
RCLKIN
RESERVED
DGND
CF
F2,F1
PIN FUNCTION DESCRIPTIONS
Description
Power Supply. This pin provides the supply voltage for the circuitry in the ADE7757. 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.
Analog Inputs for Channel V2 (voltage channel). These inputs provide a fully differential
input pair. The maximum differential input voltage is ±165 mV for specified operation. The
maximum signal level at these pins is ±165 mV 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.
Analog Inputs for Channel V1 (current channel). These inputs are fully differential voltage
inputs with a maximum signal level of ±30 mV with respect to pin V1N for specified opera-
tion. The maximum signal level at this pin is ±165 mV with respect to AGND. Both inputs
have internal ESD protection circuitry and in addition an overvoltage of ±6 V can be sus-
tained on these inputs without risk of permanent damage.
This provides the ground reference for the analog circuitry in the ADE7757, i.e., 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, e.g., antialiasing filters, current and
voltage sensors, etc. For accurate noise suppression, the analog ground plane should only be
connected to the digital ground plane at one point. A star ground configuration will help to
keep noisy digital currents away from the analog circuits.
This pin provides access to the on-chip voltage reference. The on-chip reference has a nomi-
nal value of 2.5 V ± 8% and a typical temperature coefficient of 30 ppm/°C. An external
reference source may also be connected at this pin. In either case this pin should be
decoupled to AGND with a 1 µF tantalum capacitor and 100 nF ceramic capacitor.
Select Calibration Frequency. This logic input is used to select the frequency on the calibra-
tion output CF. Table III shows calibration frequencies selection.
These logic inputs are used to select one of four possible frequencies for the digital-to-fre-
quency conversion. With this logic input, designers have greater flexibility when designing an
energy meter. See Selecting a Frequency for an Energy Meter Application.
To enable the internal oscillator as a clock source to the chip, a precise 5 kΩ resistor must be
connected from this pin to DGND.
Reserved pin. No load should be connected to this pin.
This provides the ground reference for the digital circuitry in the ADE7757, i.e., multiplier,
filters and digital-to-frequency converter. 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, e.g.,
counters (mechanical and digital), MCUs and indicator LEDs. For accurate noise suppres-
sion the analog ground plane should only be connected to the digital ground plane at one
point only, e.g., a star ground.
Calibration Frequency Logic Output. The CF logic output provides instantaneous real power
information. This output is intended for calibration purposes. Also see SCF pin description.
Low Frequency Logic Outputs. F1 and F2 supply average real power information. The logic
outputs can be used to directly drive electromechanical counters and two phase stepper mo-
tors. See Transfer Function.
REV. PrC.
PIN CONFIGURATION
SOIC-16nb Package
VDD 1
16 F1
V2P 2
15 F2
V2N 3
14 CF
V1N 4 ADE7757 13 DGND
V1P
5
TOP VIEW
(Not to Scale)
12 RESERVED
AGND 6
11 RCLKIN
REFIN/OUT 7
10 S0
SCF 8
9 S1
–5–
5 Page 
PRELIMINARY TECHNICAL DATA
ADE7757
DIGITAL-TO-FREQUENCY CONVERSION
As previously described, the digital output of the low-pass filter
after multiplication contains the real power information. How-
ever, since this LPF is not an ideal “brick wall” filter imple-
mentation, the output signal also contains attenuated
components at the line frequency and its harmonics, i.e.,
cos(hωt) where h = 1, 2, 3, . . . etc.
The magnitude response of the filter is given by:
H( f ) = 1
1
+
f2
8.9 2
(5)
For a line frequency of 50 Hz this would give an attenua-
tion of the 2ω (100 Hz) component of approximately –
22 dB. The dominating harmonic will be at twice the line
frequency (2ω) due to the instantaneous power calculation.
Figure 21 shows the instantaneous real power signal at the
output of the LPF which still contains a significant amount
of instantaneous power information, i.e., cos (2ωt). This
signal is then passed to the digital-to-frequency converter
where it is integrated (accumulated) over time in order to
produce an output frequency. The accumulation of the
signal will suppress or average out any non-dc components
in the instantaneous real power signal. The average value
of a sinusoidal signal is zero. Hence the frequency gener-
ated by the ADE7757 is proportional to the average real
power. Figure 21 shows the digital-to-frequency conver-
sion for steady load conditions, i.e., constant voltage and
current.
V
MULTIPLIER
I
V×I
2
DIGITAL-TO-
FREQUENCY
∑
LPF
F1
F2
LPF TO EXTRACT
REAL POWER
(DC TERM)
DIGITAL-TO-
FREQUENCY
∑ CF
cos(2ωt )
ATTENUATED BY LPF
F1
TIME
CF
TIME
ing it to a frequency. This shorter accumulation period
means less averaging of the cos (2ωt) component. Conse-
quently, some of this instantaneous power signal passes
through the digital-to-frequency conversion. This will not
be a problem in the application. Where CF is used for
calibration purposes, the frequency should be averaged by
the frequency counter which will remove any ripple. If CF
is being used to measure energy; for example, in a micro-
processor-based application, the CF output should also be
averaged to calculate power.
Because the outputs F1 and F2 operate at a much lower
frequency, a lot more averaging of the instantaneous real
power signal is carried out. The result is a greatly attenu-
ated sinusoidal content and a virtually ripple-free fre-
quency output.
Interfacing the ADE7757 to a Microcontroller for Energy
Measurement
The easiest way to interface the ADE7757 to a
microcontroller is to use the CF high frequency output
with the output frequency scaling set to 2048 x F1, F2.
This is done by setting SCF = 0 and S0 = S1 = 1, see
Table III. With full-scale ac signals on the analog inputs,
the output frequency on CF will be approximately
2.867 kHz. Figure 22 illustrates one scheme which could
be used to digitize the output frequency and carry out the
necessary averaging mentioned in the previous section.
CF
AVERAGE
FREQUENCY
FREQUENCY
RIPPLE
±10%
ADE7757
CF
TIME
MCU
COUNTER
TIMER
0 ω 2ω
FREQUENCY (RAD/S)
INSTANTANEOUS REAL POWER SIGNAL
(FREQUENCY DOMAIN)
Figure 21. Real Power-to-Frequency Conversion
As can be seen in the diagram, the frequency output CF is
seen to vary over time, even under steady load conditions.
This frequency variation is primarily due to the cos (2ωt)
component in the instantaneous real power signal. The
output frequency on CF can be up to 2048 times higher
than the frequency on F1 and F2. This higher output fre-
quency is generated by accumulating the instantaneous
real power signal over a much shorter time while convert-
Figure 22. Interfacing the ADE7757 to an MCU
As shown, the frequency output CF is connected to an
MCU counter or port. This will count the number of
pulses in a given integration time which is determined by
an MCU internal timer. The average power is propor-
tional to the average frequency is given by:
Average Frequency = Average Power = Counter
Time
The energy consumed during an integration period is
given by:
Energy = Average Power ×Time = Counter × Time = Counter
Time
REV. PrC.
–11–
11 Page | ||
| Páginas | Total 14 Páginas | |
| PDF Descargar | [ Datasheet ADE7757.PDF ] | |
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