SPEC-1081 (REV. 2)

11/15

29-09-2017

SA4101A

TYPICAL APPLICATION

The following description outlines the basic process required

to design a typical single phase energy meter using the

SA4101A and a shunt resistor as a current sensing element.

The meter is capable of measuring 220V/40A/50Hz with a

precision better than Class 1. It uses a stepper motor counter

with 100imp/kWh and the calibration LED has a constant of

1600imp/kWh.

The most important external circuits required for the

SA4101A are the current input network, the voltage input

network as well as the bias resistor. All resistors should be

1% metal film resistors of the same type to minimize

temperature effects.

Bias Resistor

A bias resistor of R10 = 47k

 sets optimum bias and

reference currents on chip. Calibration of the meter should be

done using the voltage input and not by means of the bias

resistor.

Current Input Network

The voltage drop across the shunt resistor at maximum rated

. A 320μ

 shunt is chosen which sets the voltage

drop at maximum rated current to 12.8mV and the maximum

power dissipation in the shunt to 0.5W. The voltage across

the shunt resistor is converted to the required differential

input currents through the current input resistors. Anti-alias

filters are incorporated on these input resistors to filter any

high frequency signal components that could affect the

performance of the SA4101A.

The four current input resistors (R1, R2, R3, R4) should be of

equal size to optimize the input networks low pass filtering

characteristics, so the values can be calculated as follows:

4 × 16��������

For optimum performance the cut-off frequency of the anti-

alias filter should be between 10kHz and 20kHz. The

so the capacitor values should be in the order of

����1 = ����2 =

1

=

1

���� × 15������������ × 200Ω

current input network.

Voltage Input Network

The voltage sense input requires an input current of 14

voltage divider to a lower voltage that is converted to the

required input current by means of the input resistor. Once

again an anti-alias filter is required to remove any high

frequency signals that could affect the performance of the

SA4101A. A shunt typically has very little phase shift so

phase compensation is not required.

The input resistor R8 sets the current input into the device.

This resistor should not be too large else the capacitor for the

anti-alias filter will be quite small which could cause

inaccurate phase shift due to parasitic capacitances.

Therefore R8 = 100k

 is chosen and the voltage at the centre

of the trimpot should be 1.4V (14

μA x 100k

). The calibration

range of the voltage input network should be about ±15% to

ensure that all component tolerances can be catered for, so

the total tuning range can be set to ±0.22V. Therefore the

voltage across the trimpot and R9 is 1.62V. Choosing a 1k



trimpot results in

����9 =

1����Ω

(2 × 0.22)

× (1.62 − 2 × 0.22) ≈ 2.7����Ω

The effect of R8 can be ignored in the above equation, given

the fact that R8 is significantly larger than P1 and R9. Now let

220����

1.62����

− 1) ≈ 499����Ω

so choose R5 = R6 = 200k

and R7 = 100k.

The cut-off frequency of the anti-alias filter is adjusted so that

it is identical to that of the current input network anti-alias

filters. This ensures that the phase shift caused by the anti-

alias filters is identical on the current and voltage input

networks. Therefore

1

=

1

2����(����1 + ����9) × ����3

and so C3 = 2.7nF.