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SA9105F

THREE PHASE BIDIRECTIONAL POWER/ENERGY METERING IC WITH INSTANTANEOUS PULSE OUTPUT

South African Micro Electronic Systems 

SA9105F

C , C , C and C are the outer loop capacitors for the integrated oversampling

7 9 10

11

A/D converters. The typical value of C7 is 2.2nF and the value of C9, C10 and C11 is

560pF.

The actual values determine the signal to noise and stability performance. The tolerances

should be within ± 10%.

C4, C5, C6 and C8 are the inner loop capacitors for the integrated oversampling A/D

converters. The typical value of C4, C5, C6 and C8 is 3.3nF. Values smaller than 0.5nF

and larger than 5nF should be avoided.

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

inputs of the SA9105F through current setting resistors (R8 ..R13).

The resistor values should be selected for an input current of 16µARMS into the SA9105F,

at the rated line current.

The values of these resistors should be calculated as follows:

Phase 1:

R8 = R9 = (IL1/16µARMS) * R18/2

Phase 2:

R

10

=

R

11

=

(IL2/16µARMS)

*

R /2

19

Phase 3:

R

12

=

R

13

=

(IL3/16µARMS)

*

R /2

20

Where I

LX

= Secondary CT current at rated conditions.

R18, R19 and R20 = Current transformer termination resistors for the three phases.

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 14µARMS for nominal line voltage. Capacitors C1, C2 and C3

are for decoupling and phase compensation.

R + P defines all

14

14

on-chip bias and reference currents.

With

R+

14

P

14

=

24kΩ,

optimum

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

to R

14

will affect the output quadratically (i.e:

∆R = +5%, ∆f = +10%).

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.

8/12

sames

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