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4/14

PRELIMINARY

PM4104APDA

Current Input Filtering

For best immunity to electromagnetic disturbances the

SA4104A/B requires low-pass filters on the current sense

inputs. Referring to Figure 2 and Figure 3, 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 equivalent resistance associated with each

order of

C

C

CI

C

R

f

1

C2

C1

=

p

=

=

filters of the current input networks.

The current input network on the PM4104APDA has been

simplicity. The resulting cut-off frequency is 15.9kHz.

Voltage Sense Input Network

The voltage input network on the PM4104APDA has been

designed for operation at both 220V and 110V mains

voltage. The mains voltage is selected by means of a

jumper (J1). The voltage input network attenuates the mains

voltage signal to a lower voltage by means of a voltage

divider. A trimpot is used to tap this voltage divider at

different levels to effect calibration.

Figure 4 shows the voltage sense input network as

implemented on the PM4104APDA. The voltage sense input

of the SA4104A/B saturates at an input current of

mains voltage variation of up to +30% and –50% without

saturating the voltage sense input.

The input resistor R12 sets the current input into the device.

This resistor should not be too large else the capacitor for

the low-pass filter will be quite small. This could cause

inaccurate phase shift due to parasitic capacitances and

affect the performance of the energy meter at low power

factor. Therefore R12 = 100k

W is chosen. For the purpose

of the evaluation module a very large tuning range on the

trimpot is selected, so let R11 and P1 be 1k

W each and the

voltage over the combination of R11 and P1 be 1.76V. This

allows the input currents on the voltage sense inputs of the

The following equations can be used to obtain the remaining

resistor values:

W

+

+

+

+

W

=

k

2

10

R

9

R

8

R

7

R

k

2

V

220

V

76

.

1

and

W

+

+

W

=

k

2

8

R

7

R

k

2

V

110

V

76

.

1

This results in R7 + R8 = 123k

W and R9 + R10 = 125kW and

the values are chosen as R7 = 75k

W, R8 = 47kW and R9 =

R10 = 62k

W. The effect of R12 can be ignored in the above

equations, given the fact that R12 is significantly larger than

the combination of P1 and R11.

A low-pass filter is required on the voltage sense input to

remove any high frequency signals that could affect the

performance of the SA4104A/B. If a current transformer is

used as a current sensing element then this low pass filter is

used to compensate for the phase shift of the current

transformer as well by purposefully increasing the cut-off

frequency.

R12

R9

IVP

GND

C3

R8

R7

GND

V

NOM

(220V / 110V)

(11µA

Live

Neutral

GND

R11

P1

SA4104A

SA4104B

AGND

JS2 “L”

JS2 “N”

R10

GND

J1

110V / 220V

R12

R9

IVP

GND

C3

R8

R7

GND

V

NOM

(220V / 110V)

(11µA

Live

Neutral

GND

R11

P1

SA4104A

SA4104B

AGND

JS2 “L”

JS2 “N”

R10

GND

J1

110V / 220V

Figure 4: Voltage input network on the PM4104APDA