SPEC-3093 (REV. 2)

7/15

29-09-2017

SA4305A

FUNCTIONAL DESCRIPTION

Theory of Operation

The SA4305A includes all the required functions for three

phase power and energy measurement. Three pairs of

identical AD converters sample the three phase voltage and

current input signals. The three pairs of digital signals,

accurately representing the voltage and current inputs, are

multiplied using digital multiplication. The output of each

multiplier represents the instantaneous power on each

channel. The three channels are added together and the

pulse generation circuit creates a pulse output where the

instantaneous frequency is proportional to the instantaneous

power measured. The addition of the three channels can be

programmed to arithmetic or absolute mode. The arithmetic

mode will take the direction of energy flow into account while

the absolute mode will ignore it.

For given voltage and current signals the instantaneous

power is calculated by:

����(����) = ����(����) × ����(����)

Let

√2

and

√2

then

where

p(t) is the instantaneous power,

v(t) is the instantaneous voltage signal,

i(t) is the instantaneous current signal,

The instantaneous power output is integrated over time to

obtain the energy by simply counting the output pulses. This

removes

the

double

mains

frequency

component

cos(2(

t+)-) and the average output pulse rate is therefore

equivalent to

���� =

1

����

∫ ����(����)��������

����

0

where

P is the average power and

cos

Linearity

The SA4305A is a CMOS integrated circuit, which performs

power/energy calculations across a dynamic range of 500:1

to an accuracy that exceeds the IEC62053 specification.

Analog Inputs

The input circuitry of the current and voltage sensor inputs is

illustrated in Figure 5. These inputs are protected against

electrostatic

discharge

through

clamping

diodes.

The

generate virtual short circuits between IIP and IIN as well as

IVP and AGND. The current sense inputs (IIP and IIN) are

identical and balanced. The AD converters convert the

signals on the voltage and current sense inputs to a digital

format for further processing. All internal offsets are

eliminated

through

the

use

of

various

cancellation

techniques.

Figure 5: Analog input configuration

Digital Outputs

The calculations required for power and energy are

performed and the result is converted to pulses on the FOUT

pulse output. The instantaneous output frequency on the

pulse output is proportional to the instantaneous active power

consumption measured. The pulse output is intended for

interfacing the SA4305A to a microcontroller or similar pulse

processing circuit.

Anti-Creep Threshold

An integrated anti-creep function prevents any output pulses

from a channel appearing on the pulse output if the energy

phase shift respectively. The individual per channel creep

A

I

IIN

IIP

VDD

VSS

VDD

VSS

A

V

IVP

VDD

VSS

AGND

VOLTAGE

SENSOR

INPUT

CURRENT

SENSOR

INPUT

CURRENT

CHANNEL

ADC

VOLTAGE

CHANNEL

ADC