SA9904A 데이터 시트보기 (PDF) - South African Micro Electronic Systems

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SA9904A

Three Phase Power / Energy IC with SPI Interface

South African Micro Electronic Systems 

SA9904A

sames

FUNCTIONAL DESCRIPTION

The SA9904A 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.

The SA9904A integrates instantaneous active and reactive

power into 24 bit integrators. RMS voltage and frequency are

continuously measured and stored in the respective registers.

The mains voltage zero crossover is available on the F150

output.

The SPI interface of the SA9904A has a tri-state output that

allows connection of more than one metering device on a

single SPI bus.

INPUT SIGNALS

Analog Input Configuration

The input circuitry of the current and voltage sensor inputs is

illustrated in figure 3. 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. 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.

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

At rated current the resistor values should be selected for input

currents of 16µARMS. Referring to figure 8, the resistors R1 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 level into the current sense inputs of the SA9904A.

The current sense inputs saturates at an input current of ±25µA

peak. Resistors R25, R26 and R27 are the current transformer

termination resistors. The voltage drop across the termination

resistors should be at least 16mV at rated conditions. Values

for the current sense inputs are calculated as follows:

R1 = R2 = (IL / 16µARMS) x RSH / 2

R3 = R4 = (IL / 16µARMS) x RSH / 2

R5 = R6 = (IL / 16µARMS) x RSH / 2

Where:

IL = Line current/CT-ratio

RSH = Shunt resistor or termination resistor (R25, R26, R27).

In case a current transformer is used for current sensing the

value of RSH should be less than the resistance of the CT's

secondary winding.

Voltage Sense Input (IVP1, IVP2, IVP3)

The current into the voltage sense inputs (virtual ground)

should be set to 14µARMS at rated voltage conditions. The

individual mains voltages are divided down to 14VRMS per

phase. The resistor R8, R9 and R10 set the current for the

voltage sense inputs. The voltage sense inputs saturate at an

input current of ±25µA peak.

VDD

IIP

CURRENT

VSS

SENSOR

INPUTS

VDD

IIN

VSS

VDD

IVP

VOLTAGE

SENSOR

VSS

INPUT

AI

AV

DR-01288

GND

Figure 3: Analog input internal configuration

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