AD7751| Datasheet

Datasheet preview, take a look at Datasheets before downloading (Data Sheet is available on manufacturer site)

a
FEATURES High Accuracy, Supports 50 Hz/60 Hz IEC 521/1036 Less than 0.1% Error Over a Dynamic Range of 500 to 1 The AD7751 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 Data Continuous Monitoring of the Phase and Neutral Current Allows Fault Detection in Two-Wire Distribution Systems The 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 O
verdrive Capability Single 5 V Supply, Low Power (15 mW Typical) Low Cost CMOS Process GENERAL DESCRIPTION

Energy Metering IC with On-Chip Fault Detection AD7751*
FUNCTIONAL BLOCK DIAGRAM
G0 G1 AVDD AGND FAULT AC/DC DVDD DGND

AD7751
POWER SUPPLY MONITOR V1A V1N V1B 1, V2P V2N 1, PGA 2, 8, ADC 16 ADC PGA 2, 8, 16 ADC A<>B A>B

...110101...

SIGNAL PROCESSING BLOCK
HPF

...110101...
B>A

PHASE CORRECTION

MULTIPLIER

...11011001...
LPF

4k 2.5V REFERENCE CLKOUT REFIN/OUT CLKIN

DIGITAL-TO-FREQUENCY CONVERTER

SCF S0 S1 REVP CF F1 F2 RESET

The AD7751 is a high accuracy fault tolerant electrical energy measurement IC intended for use with two-wire distribution systems. The part specifications surpass the accuracy requirements as quoted in the IEC1036 standard. The only analog circuitry used on the AD7751 is in the 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 extremes in environmental conditions and over time. The AD7751 incorporates a novel fault detection scheme that both 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 (return) currents. A fault is indicated when these currents differ by more than 12.5%. Billing is continued using the larger of the two currents when the difference is greater than 14%.

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 issues 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. An internal no-load threshold ensures that the AD7751 does not exhibit any creep when there is no load. The AD7751 is available in 24-lead DIP and SSOP packages.

*Protected by U.S. Patent Nos. 5,745,323; 5,760,617; 5,862,069 and 5,872,469.

REV. 0
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 World Wide Web Site: http://www.analog.com Fax: 781/326-8703 Analog Devices, Inc., 1999