Energy Metering IC
With On-Chip Fault Detection
a
AD7751*
FEATURES
The only analog circuitry used in the AD7751 is in the ADCs
and reference circuit. All other signal processing (e.g., multipli-
cation and filtering) is carried out in the digital domain. This
approach provides superior stability and accuracy over extremes
in environmental conditions and over time.
High Accuracy, Supports 50 Hz/60 Hz IEC 687/1036
Less than 0.1% Error Over a Dynamic Range of 500 to 1
Supplies Average Real Power on the Frequency
Outputs F1 and F2
High-Frequency Output CF Is Intended for Calibration
and Supplies Instantaneous Real Power
Continuous Monitoring of the Phase and Neutral
Current Allows Fault Detection in Two-Wire
Distribution Systems
AD7751 Uses the Larger of the Two Currents (Phase
or Neutral) to Bill—Even During a Fault Condition
Two Logic Outputs (FAULT and REVP) Can be Used to
Indicate a Potential Miswiring or Fault Condition
Direct Drive for Electromechanical Counters and
Two-Phase Stepper Motors (F1 and F2)
A PGA in the Current Channel Allows the Use of Small
Values of Shunt and Burden Resistance
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
The AD7751 incorporates a novel fault detection scheme that
warns of fault conditions and allows the AD7751 to continue
accurate billing during a fault event. The AD7751 does this
by continuously monitoring both the phase and neutral (re-
turn) currents. A fault is indicated when these currents differ by
more than 12.5%. Billing is continued using the larger of the
two currents.
The AD7751 supplies average real power information on the
low-frequency outputs F1 and F2. These logic outputs may be
used to directly drive an electromechanical counter or interface
to an MCU. The CF logic output gives instantaneous real power
information. This output is intended to be used for calibration
purposes.
The AD7751 includes a power supply monitoring circuit on the
AVDD supply pin. The AD7751 will remain in a reset condition
until the supply voltage on AVDD reaches 4 V. If the supply falls
below 4 V, the AD7751 will also be reset and no pulses will be
issued on F1, F2, and CF.
Single 5 V Supply, Low Power (15 mW Typical)
Low-Cost CMOS Process
Internal phase matching circuitry ensures that the voltage and
current channels are matched whether the HPF in Channel 1 is
on or off. The AD7751 also has anticreep protection.
GENERAL DESCRIPTION
The AD7751 is a high-accuracy fault-tolerant electrical energy
measurement IC that is intended for use with 2-wire distribution
systems. The part specifications surpass the accuracy require-
ments as quoted in the IEC1036 standard.
The AD7751 is available in 24-lead DIP and SSOP packages.
FUNCTIONAL BLOCK DIAGRAM
FAULT
AC/DC DV
DGND
G0 G1
AV
AGND
DD
DD
AD7751
POWER
SUPPLY MONITOR
SIGNAL
PROCESSING
BLOCK
A<>B
A
V1A
V1N
V1B
...110101...
ADC
PGA
HPF
A>B
⌽
PHASE
...110101...
B
ADC
CORRECTION
MULTIPLIER
B>A
PGA
LPF
V2P
V2N
...11011001...
ADC
DIGITAL-TO-FREQUENCY
CONVERTER
4k⍀
2.5V
REFERENCE
F1
REF
CLKIN CLKOUT SCF S0 S1 REVP CF
F2RESET
IN/OUT
*US Patent 5,745,323; 5,760,617; 5,862,069; 5,872,469.
REV. A
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, U.S.A.
Tel: 781/329-4700
Fax: 781/326-8703
World Wide Web Site: http://www.analog.com
© Analog Devices, Inc., 2000
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