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SA9110AFA

MONOCHIP THREE PHASE BIDIRECTIONAL KILOWATT HOUR METERING IC

South African Micro Electronic Systems 

SA9110A

FUNCTIONAL DESCRIPTION

The SA9110A is a CMOS mixed signal Analog/Digital integrated circuit, which performs

three phase energy calculations across a power range of 1000:1, to an overall accurancy

of better than Class 1. An on-chip LCD driver directly drives a 7 digit (7 segment) LCD.

Also included on-chip, are 4 x tariff registers externally selectable for multi-tariff energy

metering applications and a fifth register which retains the total energy consumption.

The integrated circuit includes all the required functions such as two oversampling A/D

converters for the voltage and current sense inputs, power calculation and energy

integration. Offset is eliminated through the use of internal cancellation procedures.

1. Power Calculation

In the Application Circuit (Figure 1), the mains voltage from Line 1, Line 2 and Line

3, are converted to currents and applied to the voltage sense inputs IVP1, IVP2 and

IVP3.

The current levels on the voltage sense inputs are derived from the mains voltage

(3 x 230 VAC) being divided down through voltage dividers to 14V. The resulting

input currents into the A/D converters are 14µA through the resistors R15, R16 and

R17.

For the current sense inputs the voltage drop across the current transformers

terminating resitors are converted to currents of 16µA for rated conditions, by means

of resistors R , R (Phase 1); R , R (Phase 2) and R , R (Phase 3).

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The signals providing the current information are applied to the current sensor inputs

IIN1, IIP1, IIN2, IIP2 and II3, IIP3.

A pulse rate output for calibration purposes is available on SDO (Pin 62), the pulse

rate being proportional to the active energy consumption.

The integrated anti-creep function ensures no metering when no line current is

present.

2. Analog Input Configuration

The input circuitry of the current and voltage sensor inputs are illustrated below.

These inputs are protected against electrostatic discharge through clamping

diodes.

The feedback loops from the outputs of the amplifiers AI and AV generate virtual

shorts on the signal inputs. Exact duplications of the input currents are generated

for the analog signal processing circuitry.

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