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ADE7757ARN Schematic ( PDF Datasheet ) - Analog Devices

Teilenummer ADE7757ARN
Beschreibung Energy Metering IC with Integrated Oscillator
Hersteller Analog Devices
Logo Analog Devices Logo 




Gesamt 14 Seiten
ADE7757ARN Datasheet, Funktion
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






ADE7757ARN Datasheet, Funktion
PRELIMINARY TECHNICAL DATA
ADE7757 –Typical Performance Characteristics
TBD TBD
Figure 2. Error as a % Reading over Temperature on-chip
reference (PF=1)
Figure 5. Error as a % of Reading over Temperature with
External Reference (PF=0.5)
TBD TBD
Figure 3. Error as a % of Reading over Temperature with
on-chip reference (PF=0.5)
TBD
Figure 6. Error as a %of Reading over Input Frequency
602k
220V 200150nF
40A TO
40mA
500 µΩ
200
150nF
200
150nF
200
150nF
1µF 100nF
VDD
100nF
10µF
VDD
V2P
F1
U1 F2
ADE7757 CF
U3 K7
V2N
RESERVED
V1P
RCLKIN
5 k
K8
PS2501-1
VDD
V1N
S0
REFIN/OUT
S1
SCF
AGND DGND
10k
10nF 10nF 10nF
Figure 4. Error as a % of Reading over Temperature with
External Reference (PF=1)
–6–
Figure 7. Test Circuit for Performance Curves
REV. PrC.

6 Page









ADE7757ARN pdf, datenblatt
ADE7757
PRELIMINARY TECHNICAL DATA
For the purpose of calibration, this integration time could
be 10 to 20 seconds in order to accumulate enough pulses
to ensure correct averaging of the frequency. In normal
operation the integration time could be reduced to one or
two seconds depending, for example, on the required up-
date rate of a display. With shorter integration times on
the MCU the amount of energy in each update may still
have some small amount of ripple, even under steady load
conditions. However, over a minute or more the measured
energy will have no ripple.
Power Measurement Considerations
Calculating and displaying power information will always
have some associated ripple that will depend on the inte-
gration period used in the MCU to determine average
power and also the load. For example, at light loads the
output frequency may be 10 Hz. With an integration pe-
riod of two seconds, only about 20 pulses will be counted.
The possibility of missing one pulse always exists as the
ADE7757 output frequency is running asynchronously to
the MCU timer. This would result in a one-in-twenty or
5% error in the power measurement.
TRANSFER FUNCTION
Frequency Outputs F1 and F2
The ADE7757 calculates the product of two voltage signals (on
Channel V1 and Channel V2) and then low-pass filters this
product to extract real power information. This real power
information is then converted to a frequency. The frequency
information is output on F1 and F2 in the form of active low
pulses. The pulse rate at these outputs is relatively low,
e.g., 0.175 Hz maximum for ac signals with S0 = S1 =
0see Table II. This means that the frequency at these
outputs is generated from real power information accumu-
lated over a relatively long period of time. The result is an
output frequency that is proportional to the average real
power. The averaging of the real power signal is implicit
to the digital-to-frequency conversion. The output fre-
quency or pulse rate is related to the input voltage signals
by the following equation:
Freq
=
515.84
×V1rms × V
Vref 2
2 rms
×
F14
where:
Freq = Output frequency on F1 and F2 (Hz)
V1rms = Differential rms voltage signal on Channel V1
(volts)
V 2rms = Differential rms voltage signal on Channel V2
(volts)
Vref = The reference voltage (2.5 V ± 8%) (volts)
F14 = One of four possible frequencies selected by us-
ing the logic inputs S0 and S1see Table I.
Table I. F1–4 Frequency Selection
S1 S0
F1–4 (Hz)
00
01
10
11
0.85
1.7
3.4
6.8
NOTE
*F14 is a binary fraction of the internal oscillator frequency
Example
In this example, with ac voltages of ±30 mV peak applied
to V1 and ±165 mV peak applied to V2, the expected
output frequency is calculated as follows:
F14 = 0.85 Hz, S0 = S1 = 0
V1rms = 0.03/ 2 volts
V 2rms = 0.165/ 2 volts
Vref = 2.5 V (nominal reference value).
NOTE: If the on-chip reference is used, actual
output frequencies may vary from device to device
due to reference tolerance of ±8%.
Freq = 515 .85 × 0.03 × 0.165 × 0.85 = 0.175
2 × 2 × 2.52
Table II. Maximum Output Frequency on F1 and F2
S1 S0
00
01
10
11
Max Frequency
for AC Inputs (Hz)
0.175
0.35
0.7
1.4
Frequency Output CF
The pulse output CF (Calibration Frequency) is intended for
calibration purposes. The output pulse rate on CF can be up to
2048 times the pulse rate on F1 and F2. The lower the F14
frequency selected, the higher the CF scaling (except for the
high frequency mode SCF = 0, S1 = S0 = 1). Table III shows
how the two frequencies are related, depending on the states of
the logic inputs S0, S1 and SCF. Due to its relatively high
pulse rate, the frequency at CF logic output is proportional to
the instantaneous real power. As with F1 and F2, CF is derived
from the output of the low-pass filter after multiplication. How-
ever, because the output frequency is high, this real power
information is accumulated over a much shorter time. Hence
less averaging is carried out in the digital-to-frequency con-
version. With much less averaging of the real power signal, the
CF output is much more responsive to power fluctua-
tionssee Signal Processing Block in Figure 11.
–12–
REV. PrC.

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