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April 2007 Rev 1 1/38
AN2512
Application note
Three-phase meter based STPM01, VIPer12A
Introduction
This application note describes how to design a three-phase meter using STPM01 as the
measuring device and a VIPer12A based SMPS (Switch Mode Power Supply).
STPM01 is a metering ASSP implemented in an advanced 0.35 µm BCD6 technology. It is
designed for the effective measurement of active, reactive and apparent energies, Vrms,
Irms, instantaneous voltage and current, frequency in power line systems that use the
current transformer, Rogowski coil and/or shunt principle.
This device can be used as a standalone on-board metering device in single-phase energy
meter applications or as a peripheral in a microprocessor based single- or three-phase
meter.
In a standalone configuration STPM01 outputs a pulse train signal having a frequency
proportional to the active power used, while in peripheral mode STPM01 is used in a
microprocessor based application. In this case, measured data are read at a fixed time
interval from the device internal registers by means of SPI interface processed by a
microcontroller.
In the following paragraphs a circuit description is explained, with particular focus on the
power supply section, the three-phase design, and the clock management network. Then,
the power calculation algorithm is discussed and finally some layout hints and experimental
results are shown.
This application note should be used in conjunction with the STPM01 and VIPer12A
datasheet.
Three phase block diagram
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