ADE7757 Datasheet, PDF (1/14 Pages) Analog Devices – Energy Metering IC with Integrated Oscillator

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 V_DD supply pin. The ADE7757 will remain in reset
mode until the supply voltage on V_DD 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
V_DD AGND
DGND
V2P
V2N
V1N
V1P
ADE7757
POWER
SUPPLY MONITOR
∑ ∆ ^...110101...
ADC
MULTIPLIER
SIGNAL
PROCESSING
BLOCK
LPF
∑∆
ADC
PHASE
CORRECTION _HPF
. . .11011001. . .
Φ
2.5V
4kV
REFERENCE
INTERNAL
OSCILLATOR
DIGITAL-TO-FREQUENCY
CONVERTER
REF_IN/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.
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© Analog Devices, Inc., February 2002