SA9105EFA View Datasheet(PDF) - South African Micro Electronic Systems
Part Name
Description
Manufacturer
SA9105EFA
South African Micro Electronic Systems
SA9105EFA Datasheet PDF : 12 Pages
| |||
SA9105E
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 SA9105E integrated circuit are:
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 C is 2.2nF and the value of C , C and C is
7
9 10
11
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 SA9105E through current setting resistors (R8 ..R13).
The resistor values should be selected for an input current of 16µA into the SA9105E, at
the rated line current.
The values of these resistors should be calculated as follows:
Phase 1:
R
8
=
R
9
=
(IL1/16µA)
*
R /2
18
Phase 2:
R
10
=
R
11
=
(IL2/16µA)
*
R /2
19
Phase 3:
R12 = R13 = (IL3/16µA) * R20/2
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 14µA 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%).
sames
43/12
Share Link: