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SA9605APA

THREE PHASE POWER/ENERGY METERING IC WITH INSTANTANEOUS PULSE OUTPUT

South African Micro Electronic Systems 

SA9605A

The only changes which now have to be implemented to interface the device to different

rated systems are: change the current sense resistors; and select the required PGM0

and PGM1.

No change to the post divider or micro-controller software is required if the FOUT2 pin

is used as described.

TYPICAL APPLICATION

In the Application Circuit (Figure 1), the components required for a three phase power

metering application are shown.

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

inputs of the SA9605A through current setting resistors (R8 ..R13).

The resistor values for standard operation are selected for an input current of 16µA into

the SA9605A, at the rated line current.

The values of these resistors are calculated as follows:

Phase 1:

R

8

=

R

9

=

(IL1/16µA)

*

R /2

18

Phase 2:

R10 = R11 = (IL2/16µA) * R19/2

Phase 3:

R

12

=

R

13

=

(IL3/16µA)

*

R /2

20

Where I

LX

= Secondary CT current at rated conditions.

R , R and R = Current transformer termination resistors for the three phases.

18 19

20

R + R , R and R set the current for the phase 1 voltage sense input. R + R , R +

1

1A 4

15

2

2A 5

P and R set the current for phase 2 and R + R , R + P and R set the current for phase

5

16

3

3A 6

6

17

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

(virtual ground) are set to 14µA for rated line voltage. Capacitors C1, C2 and C3 are for

decoupling and phase compensation.

R14 + P14 defines all on-chip bias and reference currents. With R14+ P14 = 24kΩ, optimum

conditions are set. R14 + P14 may be varied within ± 10% for calibration purposes. Any

changes to R14 + P14 will affect the output quadratically (i.e: ∆R = +5%, ∆f = +10%).

The formula for calculating the Output Frequency (f) is given below:

FOSC

(I I ) + (I I ) + (I I )

f = 11.16 * FOUTX * 3.5795MHz *

I1 V1

I2 V2

3 * IR2

I3 V3

Where FOUTX = Nominal rated frequency (1160Hz)

FOSC = Oscillator frequency (2MHz ...... 4MHz)

I , I , I = Input currents for current inputs (16µA at rated)

I1 I2 I3

IV1, IV2, IV3 = Input currents for voltage inputs (14µA at rated)

IR

= Reference current (typically 50µA)

sames

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