SA9904B Datasheet, PDF (4/12 Pages) List of Unclassifed Manufacturers – Three Phase Power / Energy IC with SPI Interface

SA9904B
sames
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.
Calibration LED
VDD
IIP
CURRENT
VSS
SENSOR
AI
INPUTS
VDD
IIN
VSS
VDD
Voltage
Sensing
SA9904B
Active Energy
Reactive Energy
VRMS and
Frequency
Measurements
SPI
Micro-
Controller
EEPROM LCD
IVP
VOLTAGE
SENSOR
VSS
INPUT
A_V
Power
Supply
N L1 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
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.
INPUT SIGNALS
Analog Input Configuration
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 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 (IMAX) the resistor values should be selected for
input currents of 16µARMS. Referring to figure 5, the resistors R1
DR-01288
GND
Figure 4: Analog input internal configuration
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:
R1 = R2 = (IL / 16µARMS) x Rsh / 2
R3 = R4 = (IL / 16µARMS) x Rsh / 2
R5 = R6 = (IL / 16µARMS) x Rsh / 2
Ch3 In
CH2 In
CH1In
Neutral
GND
IMAX
IMAX
CT1
IMAX
CT2
CT3
CH3 Out
CH2 Out
CH1 Out
R1
16µARMS
IIN1
Rsh1 > 20mVRMS
GND
R2
IIP1
R3
16µARMS
IIN2
Rsh2
> 20mVRMS
R4
GND
R5
16µARMS
SA9904B
IIP2
IIN3
Rsh3 > 20mVRMS
R6
GND
IIP3
Dr-01644
Figure 5: Current sense input configuration
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