SA9110A

14/18

sames

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 SA9110A 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 SA9110A through current setting resistors (R

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

µA

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

the current for phase 2 and R

be selected so that the input currents into the voltage sense inputs (virtual ground) are

set to 14

µA

phase compensation.

R

With R

conditions are set. R

to R

∆R = +5%, ∆f = +10%).

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

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

A/D converters.