SA9105A

sames

7/12

TYPICAL APPLICATION

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

metering application are shown. Terminated current transformers are used for current

sensing.

The most important external components for the SA9105A integrated circuit are:

C

A/D converters. The typical value of C

560pF.

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

should be within ± 10%.

C

converters. The typical value of C

and larger than 5nF should be avoided.

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

inputs of the SA9105A through current setting resistors (R

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

µA into the SA9105A at

the rated line current.

The values of these resistors should be calculated as follows:

Phase 1:

R

Phase 2:

R

Phase 3:

R

Where I

LX

=

Secondary CT current at rated conditions.

R

=

Current transformer termination resistors for the three phases.

R

R

P

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

(virtual ground) are set to 14

µA for nominal line voltage. Capacitors C1, C2 and C3 are

for decoupling and phase compensation.

R

conditions are set. R

to R

∆R = +5%, ∆f = +10%).