STPM01 datasheet(12/56 Pages) STMICROELECTRONICS

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Terminology

STPM01

12/56

Terminology

6.1

Measurement error

The error associated with the energy measurement made by the STPM01 is defined as:

Percentage Error = [STPM01 (reading) - True Energy] / True Energy

6.2

ADC Offset error

This is the error due to the DC component associated with the analog inputs of the A/D

converters. Due to the internal automatic DC offset cancellation the STPM01 measurement

is not affected by DC components in voltage and current channel. The DC offset

cancellation is implemented in the DSP.

6.3

Gain error

The gain error is gain due to the signal channel gain amplifiers. This is the difference

between the measured ADC code and the ideal output code. The difference is expressed as

percentage of the ideal code.

6.4

Power supply DC and AC Rejection

This parameter quantifies the STPM01 measurement error as a percentage of reading when

the power supplies are varied. For the PSRRAC measurement, a reading at two nominal

supplies voltages (3.3 and 5 V) is taken. A second reading is obtained with the same input

signal levels when an ac (200 mVrms/100 Hz) signal is introduced onto the supplies. Any

error introduced by this ac signal is expressed as a percentage of reading.

For the PSRRDC measurement, a reading at two nominal supplies voltages (3.3 and 5V) is

taken. A second reading is obtained with the same input signal levels when the supplies are

varied ±10%. Any error introduced is again expressed as a percentage of the reading.

6.5

Conventions

The lowest analog and digital power supply voltage is named VSS which represent the

system Ground (GND). All voltage specifications for digital input/output pins are referred to

GND.

Positive currents flow into a pin. Sinking current means that the current is flowing into the pin

and then it is positive. Sourcing current means that the current is flowing out of the pin and

then it is negative.

Timing specifications of signal treated by a digital control part are relative to CLKOUT. This

signal is provided from the crystal oscillator of 4.194MHz nominal frequency or from the

internal RC oscillator, eventually an external source of 4.194MHz or 8.192MHz can be used.

Timing specifications of signals of the SPI interface are relative to the SCLNLC, there is no

direct relationship between the clock (SCLNLC) of the SPI interface and the clock of the

DSP block.

A positive logic convention is used in all equations.

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