PM9105AF
The values of these resistors should be calculated as follows:
Phase 1:
R
8
= R
9
= (I
L1
/16µA) x R
18
/2
Phase 2:
R
10
= R
11
= (I
L2
/16µA) x R
19
/2
Phase 3:
R
12
= R
13
= (I
L3
/16µA) x R
20
/2
Where I
LX
=
Secondary CT current at rated conditions.
R
18
, R
19
and R
20
=
Termination resistors of the three current transformers.
R
1
+ R
1A
, R
4
and R
15
set the current for the phase 1 voltage sense input. R
2
+ R
2A
,
R
5
+ P
5
and R
16
set the current for phase 2 and R
3
+ R
3A
, R
6
+ P
6
and R
17
set the current
for Phase 3. The values should be selected so that the input currents into the voltage
sense inputs (virtual ground) is set to 14µA at nominal line voltage. Capacitors C1,
C2 and C3 are for decoupling and phase compensation.
R
14
+ P
14
defines all on-chip bias and reference currents. With R
14
+ P
14
= 24kΩ,
optimum conditions are set. P
14
may be varied within ± 10% for calibration purposes.
Any changes to R
14
will affect the output quadratically (i.e:
∆R
= +5%,
∆FOUT
=
+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.
sames
5/10
SAMES [ SAMES ]
