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sames

SA9904B

http://www.sames.co.za

FUNCTIONAL DESCRIPTION

The SA9904B is a CMOS mixed signal Analog/Digital integrated

circuit, which performs the measurement of active power,

reactive power, RMS voltage and mains frequency. The

integrated circuit includes all the required functions for three-

phase power and energy measurement such as oversampling

A/D converters for the voltage and current sense inputs, power

calculation and energy integration.

and R2 on current channel 1, resistors R3 and R4 on current

channel 2 and resistors R5 and R6 on current channel 3, define

the current levels into the SA9904B current sense inputs. The

current sense inputs saturates at ±25µA peak. Resistors Rsh1,

Rsh2 and Rsh3 are the current transformer termination

resistors. The voltage drop across the termination resistors

should be at least 20mV but not higher than 200mV. The ideal

value should be approximately 100mV at rated conditions.

Values for the current sense inputs are calculated as follows:

R = R = ( /

)xRsh/2

12

I

16µA

R = R = (I / 16µA

) x Rsh / 2

R = R = (I / 16µA

) x Rsh / 2

L

RMS

3

4

L

RMS

5

6

L

RMS

Figure 3:

Typical architecture of an energy meter using the

SA9904B

The SA9904B integrates instantaneous active and reactive

power into 24 bit registers. RMS voltage and frequency are

continuously measured and stored in the respective registers.

The mains voltage zero crossover is available on the F50 output.

The SPI interface of the SA9904B has a tri-state output that

allows connection of more than one metering device on a single

SPI bus.

The input circuitry of the current and voltage sensor inputs is

illustrated in figure 4. These inputs are protected against

electrostatic discharge through clamping diodes. The feedback

loops from the outputs of the amplifiers A and A generate

virtual shorts on the signal inputs. Exact duplications of the input

currents are generated for the analog signal processing

circuitry. The current and voltage sense inputs are identical.

Both inputs are differential current driven up to ±25µA peak. One

of the voltage sense amplifier input terminals is internally

connected to GND. This is possible because the voltage sense

input is much less sensitive to externally induced parasitic

signals compared to the current sense inputs.

At rated current (I

) the resistor values should be selected for

input currents of 16µA

. Referring to figure 5, the resistors R1

INPUT SIGNALS

Analog Input Configuration

Current Sense Inputs (IIN1, IIP1, IIN2, IIP2, IIN3, IIP3)

IV

RMS

MAX

Figure 4: Analog input internal configuration

VOLTAGE

SENSOR

INPUT

IVP

DR-01288

SS

V

CURRENT

SENSOR

INPUTS

IIP

IIN

SS

V

VDD

SS

V

VDD

DD

V

GND

Figure 5: Current sense input configuration

Voltage

Sensing

Power

Supply

SA9904B

Active Energy

Reactive Energy

V

and

Frequency

Measurements

RMS

Calibration LED

Micro-

Controller

LCD

EEPROM

SPI

NL1

L2 L3

A micro-controller in addition to communicating

with the SA9904B is used to read/write

parameters to the EEPROM, output pulses for

fast calibration and to display the consumed

active and reactive power, Vrms and mains

frequency information. Other parameters such

as Irms, phase angle etc. can be accurately

calculated.

Dr-01643

R1

R2

R3

R4

R5

R6

CH1In

CH2 In

Ch3 In

Rsh1

CT1

CT2

CT3

Rsh2

Rsh3

GND

GND

GND

CH3 Out

CH2 Out

CH1 Out

IIP1

IIN1

IIP2

IIN2

IIP3

IIN3

Neutral

GND

SA9904B

16µA

RMS

16µA

RMS

16µA

RMS

> 20mV

RMS

> 20mV

RMS

> 20mV

RMS

Dr-01644