SA4106A
INPUT SIGNALS
Voltage Reference (VREF)
Voltage Sense Input (IVP)
A bias resistor of 47k sets optimum bias and reference
conditions on chip. Calibration of the SA4106A should be
done on the voltage input and not on the VREF input.
Figure 8 shows the voltage sense input configuration. The
voltage sense input saturates at an input current of
±17.6μARMS (±25μAPEAK). The current into the voltage sense
input should therefore be set between 11μARMS and 12μARMS
at nominal mains voltage (VNOM) to allow for a mains voltage
variation of up to +30% and –50% without saturating the
voltage sense input. Typical VNOM values and the
corresponding IVP input currents are shown in the following
table.
Current Sense Inputs (IIP and IIN)
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.
Table 1: IVP input current for typical values of VNOM
VNOM (V)
110 / 220
115 / 230
120 / 240
IVP Input Current (μARMS)
11
11.5
12
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
.
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.
For best performance the SA4106A also requires an anti-
alias filter on the voltage sense input. Referring to Figure 8,
the capacitor C1 is used to implement the anti-alias filter. If a
current transformer is used as a current sensing element then
C1 is also used to compensate for any phase shift caused by
the current transformer. The resistor R4 defines the input
current into the device. The optimum input network is
achieved by setting R4 smaller than 100k. If R4 is made too
large the capacitor C1 will be very small and the phase shift
of the input network could be affected by stray capacitances.
The potentiometer P1 is used for calibration purposes.
The resistors R1 to R4 define the current flowing into the
device. For best performance the SA4106A 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.
R1
R2
R3
VNOM (220V)
Voltage In
Neutral
P1
R4
(11µARMS
IVP
)
GND
(P1 + R5) << R4 << (R1 + R2 + R3)
C1
R5
GND
GND
R1
R2
Current In
IIP
IIN
IIP
Figure 8: Voltage sense input configuration
IMAX
16µARMS
C1
C2
GND
RSH
GND
GND
R3
R4
Current Out
R1
R2
16µARMS
CT1
C1
C2
Current In
RA
RB
IMAX
GND
R3
Current Out
IIN
R4
Figure 7: Current sense input configuration
SPEC-1587 (REV. 5)
29-09-2017
9/18
SAMES [ SAMES ]
