SA4106ASAR datasheet(9/18 Pages) SAMES

9 / 18 page

SPEC-1587 (REV. 5)

9/18

29-09-2017

SA4106A

INPUT SIGNALS

Voltage Reference (VREF)

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.

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.

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.

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.

Figure 7: Current sense input configuration

Voltage Sense Input (IVP)

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.

Table 1: IVP input current for typical values of VNOM

VNOM (V)

IVP Input Current (μARMS)

110 / 220

115 / 230

11.5

120 / 240

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.

Figure 8: Voltage sense input configuration

IIN

IIP

GND

Current In

MAX

16µA

RMS

Current Out

GND

IIN

IIP

GND

CT1

Current In

MAX

16µA

RMS

Current Out

RSH

IVP

GND

NOM (220V)

(11µA

RMS)

Voltage In

Neutral

GND

(P1 + R5) << R4 << (R1 + R2 + R3)

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