STPM01 datasheet(15/56 Pages) STMICROELECTRONICS

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STPM01

Theory of operation

15/56

Theory of operation

8.1

General operation description

The STPM01 is able to perform active, reactive and apparent energy measurements, RMS

and instantaneous values for voltage and current, line frequency information.

Most of the functions are fully programmable using internal configuration bits accessible

through SPI interface. The most important configuration bits are the two Application bits

(APL - see table 1 for configuration register). Using these bits the STPM01 can be

programmed as peripheral (APL=0 or APL=1) in microcontroller based meter systems or as

standalone meter device (APL=2 or APL=3).

In standalone mode, the STPM01 is able to drive a stepper motor with the MOP and MON

pins, while some of the SPI pins (see table 1) are used to provide information on tamper, no

load and negative power.

In peripheral mode, due to the fact that the stepper motor is not used, the MOP and MON

pins are used to provide different information (see table 1), while the SPI pins are used to

communicate with the microcontroller.

The STPM01 includes internal registers that hold the useful information for the meter

system. Two kinds of active energy are available: the total active energy that includes all

harmonic content called type0 and the active energy limited to the 1st harmonic called

type1. This last energy value is obtained filtering the type0 active energy. The resolution of

both the two active energies is 20-bit. Reactive and Apparent energies are also available

with a 20-bit resolution.

STPM01 provides also the RMS values of voltage and current. Due to the modest dynamic

variation of the voltage, the RMS value is stored with a resolution of 11bit. While the RMS

current value has a resolution of 16bit. The momentary sampled value of voltage and

current are available also with a resolution of 11 and 16 bit respectively. The line frequency

value is stored with a resolution of 14 bits.

Due to the proprietary energy computation algorithm, STPM01 calibration is very easy and

fast allowing calibration in only one point over the whole current range. The calibration

parameters are stored permanently in the OTP (one time programmable) cells, preventing

calibration tampering.

8.2

Analog inputs

Input amplifiers

The STPM01 has one fully differential voltage input channel and two fully differential current

input channels.

The voltage channel consists of a differential amplifier with a gain of 4. The maximum

differential input voltage for the voltage channel is ±0.3V.

The two current channels are multiplexed (see tamper section for details) to provide a single

input to a preamplifier with a gain of 4. The output of this preamplifier is connected to the

input of a programmable gain amplifier (PGA) with possible gain selections of 2,4,6,8. The

total gain of the current channels will be then 8, 16, 24, 32. The gain selections are made by

writing to the gain register and it can be different for the two current channels. In case the

tamper function is not used, the secondary current can be disabled.

STPM01 数据表(PDF) 15 Page - STMicroelectronics

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