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SA9109BFA

MONOCHIP SINGLE PHASE BIDIRECTIONAL KILOWATT HOUR METERING IC

South African Micro Electronic Systems 

SA9109B

FUNCTIONAL DESCRIPTION

The SA9109B is a CMOS mixed signal Analog/Digital integrated circuit, which performs

power 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 display. Also

included on-chip, are 4 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 voltage drop across the shunt will be

between 0 and 16mVRMS (0 to 80A through a shunt resistor of 200µΩ). This voltage

is converted to a current of between 0 and 16µARMS, by means of resistors R1 and

R2.

The current sense input saturates at an input current of ±25µA peak.

The voltage level from the mains is divided down through a divider to 14V.This

voltage is converted to a signal current of 14µARMS into the voltage sensor input.

A pulse rate output for calibration purposes is available on SDO (Pin 39), 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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