STPM32 datasheet(30/121 Pages) STMICROELECTRONICS

30 / 121 page

Theory of operation

STPM32, STPM33, STPM34

30/121

DS10272 Rev 8

Theory of operation

8.1

General operation description

The STPM3x product family measures up to two line voltages and two line currents to

perform active, reactive and apparent power and energy, RMS and instantaneous values,

and line frequency information measurement of a single, split or poly-phase metering

system.

The STPM3x generates up to two independent train pulse output signals proportional to the

active, reactive, apparent or cumulative power. It also generates up to two programmable

interrupt output signals.

The internal register map and the configuration registers can be accessed by SPI or UART

interface.

The STPM3x converts analog signals, through four independent channels in parallel via

sigma-delta analog-to-digital converters, into a binary stream of sigma-delta signals with the

appropriate not overlapped control signal generator.

This technique fits to measure electrical line parameters (voltage and current) via analog

signals from voltage sensors and current sensors (inductive Rogowski coil, current

transformer or shunt resistors). Current channel inputs are connected, through external anti-

aliasing RC filter, to a Rogowski coil or current transformer (CT) or shunt current sensor

which converts line current into the appropriate voltage signal. Each current channel

includes a low-noise voltage preamplifier with a programmable gain. Voltage channels are

connected to a line voltage modulator (ADC). All channels have quiescent zero signal point

on GND, so the STPM3x samples differential signals on both channels with their zero point

around GND.

The converted sigma-delta signals feed an internal decimation filter stage that decimates

4 MHz bitstreams of a factor 512 allowing a 3.6 kHz bandwidth at -3 dB. The 24-bit voltage

and current data feed an internal configurable filtering block and the hardwired DSP that

performs the final computation of metrology quantities.

The STPM3x also includes two programmable temperature compensated bandgap

reference voltage generators and low drop supply voltage regulator. All reference voltages

are designed to eliminate the channel crosstalk.

The mode of operation and configuration of the device can be selected by dedicated

configuration registers.

STPM32 Datasheet(PDF) 30 Page - STMicroelectronics