PM9604/5AP

6/14

sames

7.

Circuit Description

The module is supplied from an on-board DC supply derived from the incoming

three phases.

The Application Circuit (Figure 2) details the components required for a three phase

power metering module. Terminated current transformers are used as current

sensors.

The most important external components are:

Terminated current sensors (current transformers) are connected to the current

sensor inputs of the devices through current setting resistors (R8...R13).

The resistor values should be selected for an input current of 16µA

integrated circuit current sensor inputs at the rated line current.

The values of these resistors are calculated as follows:

Phase 1:

R

Phase 2:

R

Phase 3:

R

Where

I

LX

=

Secondary CT current at rated conditions.

R

=

Termination resistors of the three current

transformers.

R

and R

3. The values should be selected so that the input current into the voltage sense

input (virtual ground) is set to 14µA

and C3 are for decoupling and phase compensation.

Resistors R

of two resistors which can be connected in parallel using JP7 to allow convertion of

the module between the SA9604A and SA9605A devices.

The SA9604A uses a reference current of 25µA ± 10% and the SA9605A reference

current is 50µA ± 10%. Inserting the jumper will connect R

thereby doubling the reference current to an appropriate level. T

calibration purposes.

XTAL is a colour burst TV crystal (f = 3.5795 MHz) for the oscillator. The oscillator

frequency is divided down to 1.7897 MHz on-chip to supply the digital circuitry and

the A/D converters.