SA9903B
FUNCTIONAL DESCRIPTION
The SA9903B 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 single-
phase power and energy measurement such as two
oversampling A/D converters for the voltage and current sense
inputs, power calculation and energy integration.
The SA9903B integrates instantaneous active and reactive
power in 24 bit integrators. RMS voltage and frequency is
continuously measured and stored in respective registers. The
mains voltage zero crossover is available on the FMO output.
The SPI interface of the SA9903B has a tri-state output that
allows connection of more than one metering device on a
single SPI bus.
sames
Current Sense Input (IIP and IIN)
Figure 8 shows the typical connections for the current sensor
input. The resistor R6 and R7 define the current level into the
current sense inputs of the SA9903B. At rated current the
resistor values should be selected for input currents of
16µA
RMS
. Values for resistors R6 and R7 may be calculated as
follows:
R6 = R7 = (I
L
/ 16µA ) x RSH / 2
Where I
L
= Max line current
RSH = Shunt resistor or termination resistor.
The voltage drop across RSH should not be less than 16mV at
rated currents. 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 (IVP)
The mains voltage is divided to 14V
RMS
.at nominal mains
voltage by means of resistors R1, R2, R3 and R4. The current
into the voltage sense input is set at 14µA
RMS
with resistor R5
from the voltage divider. The voltage sense input of the AD
converter saturates at an input current of ±25µA peak.
Reference Voltage (VREF)
The VREF pin is the reference for the bias resistor. With a bias
resistor of 24kW optimum conditions are set. It may be varied
within ±10% for calibration purposes.
Serial Clock (SCK)
The SCK pin is used to synchronize data interchange between
the micro controller and the SA9903B. The clock signal on this
pin is generated by the micro controller and determines the
data transfer rate of the DO and DI pins.
Serial Data In (DI)
The DI pin is the serial data input pin for the SA9903B. Data will
be input at a rate determined by the Serial Clock (SCK). Data
will be accepted only during an active chip select (CS).
A
I
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 A
I
and A
V
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.
V DD
IIP
CURRENT
SENSOR
INPUTS
VSS
VDD
IIN
VSS
VDD
Chip Select (CS)
The CS input is used to address the SA9603B. An active high
on this pin enables the SA9903B to initiate data exchange.
IVP
VOLTAGE
SENSOR
INPUT
V SS
A
V
GND
DR-01288
Figure 3: Analog input internal configuration
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