SA9903B
Linearity
INPUT SIGNALS
The SA9903B is a CMOS integrated circuit, which performs
power/energy calculations across a dynamic range of 500:1
to an accuracy that exceeds the IEC62053.
Voltage Reference (VREF)
A bias resistor of 24k sets optimum bias and reference
conditions on chip.
Analog Inputs
Current Sense Inputs (IIP and IIN)
The input circuitry of the current and voltage sensor inputs is
illustrated in Figure 6. These inputs are protected against
electrostatic discharge through clamping diodes. The
feedback loops from the outputs of the amplifiers AI and AV
generate virtual short circuits between IIP and IIN as well as
IVP and AGND. The current sense inputs (IIP and IIN) are
identical and balanced. The AD converters convert the
signals on the voltage and current sense inputs to a digital
format for further processing. All internal offsets are
eliminated through the use of various cancellation
techniques.
Figure 7 shows the typical connections for the current sensor
input when using a shunt or a current transformer as a current
sensing element. At maximum rated mains current (IMAX) the
resistor values should be selected for an input current of
16µARMS. The current sense inputs saturate at an input
current of ±17.6μARMS (±25μAPEAK), so this allows about 10%
headroom until saturation occurs.
The resistor RSH is the shunt resistor. The voltage drop
across RSH at maximum rated mains current (IMAX) should
not be less than 5mVRMS and not exceed 100mVRMS
.
VDD
The resistors RA and RB form the current transformers
termination resistor. The reference level is connected in the
centre of the termination resistor to achieve purely differential
input currents. The voltage drop across the termination
resistors at maximum rated mains current (IMAX) should be in
the order of 100mVRMS. The termination resistance should
also be significantly smaller than the DC resistance of the
current transformers secondary winding.
IIP
VSS
CURRENT
CHANNEL
ADC
CURRENT
SENSOR
INPUT
AI
VDD
IIN
VSS
VDD
The resistors R1 to R4 define the current flowing into the
device. For best performance the SA9903B requires anti-
alias filters on the current sense inputs. These filters are
realized by means of the capacitors C1 and C2. The typical
cut-off frequency of these filters should be between 10kHz
and 20kHz. The optimum input network is achieved by setting
the input resistors equal, i.e. setting R1 = R2 = R3 = R4 = RC.
This sets the equivalent resistance associated with each
capacitor to RC/2.
IVP
VOLTAGE
SENSOR
INPUT
VSS
VOLTAGE
CHANNEL
ADC
AV
AGND
Figure 6: Analog input configuration
R1
R2
Current In
IIP
IIN
IIP
IMAX
16µARMS
C1
C2
Power-On Reset
GND
RSH
GND
GND
The SA9903B has a power-on reset circuitry that activates
whenever the voltage between VDD and VSS is less than 3.6V
± 8%.
R3
R4
Current Out
R1
R2
Power Consumption
16µARMS
The power consumption of the SA9903B integrated circuit is
less than 25mW.
CT1
C1
C2
Current In
RA
RB
IMAX
GND
R3
Current Out
IIN
R4
Figure 7: Current sense input configuration
SPEC-0051 (REV. 5)
29-09-2017
9/17
SAMES [ SAMES ]
