AD7751 Datasheet, PDF (1/16 Pages) Analog Devices – Energy Metering IC With On-Chip Fault Detection

a
Energy Metering IC
With On-Chip Fault Detection
AD7751*
FEATURES
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
Single 5 V Supply, Low Power (15 mW Typical)
Low-Cost CMOS Process
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 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.
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
AV_DD supply pin. The AD7751 will remain in a reset condition
until the supply voltage on AV_DD 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.
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.
The AD7751 is available in 24-lead DIP and SSOP packages.
FUNCTIONAL BLOCK DIAGRAM
G0 G1
AV_DD AGND
FAULT
AC/DC DV_DD DGND
AD7751
POWER
SUPPLY MONITOR
SIGNAL
V1A
A< >B
...110101... A
PROCESSING
BLOCK
ADC
HPF
PGA
A >B
V1N
؋1, ؋2, ؋8, ؋16
⌽
V1B
PGA
ADC
...110101... B
B>A
PHASE
CORRECTION
MULTIPLIER
؋1, ؋2, ؋8, ؋16
LPF
V2P
. . .11011001. . .
ADC
V2N
DIGITAL-TO-FREQUENCY
2.5V
4k⍀
CONVERTER
REFERENCE
REF_IN/OUT CLKIN CLKOUT SCF S0 S1 REVP CF F1 F2 RESET
*US Patent 5,745,323; 5,760,617; 5,862,069; 5,872,469.
REV. A
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© Analog Devices, Inc., 2000