DocID027351 Rev 3
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UM1855
Hardware layout and configuration
99
Figure 14. Power measurement principle schematic diagram
A low-voltage AC generator is to be applied by the user as shown in
Figure 14
. The shunt
resistor is connected in series with the load to provide current measurement points to one of
STPMS2L input channels. The voltage measurement points for the other input channel are
taken across the load.
Figure 15
shows an extract of the corresponding schematic diagram.
Warning:
do not connect AC mains!
Test example:
The output of a low-voltage AC generator is connected to CN4, terminals 1 and 3. The
amplitude is set between 200 mV and 300 mV and the frequency adjustable between 10 Hz
and 100 Hz.
With 34 Hz frequency and the load formed of R27 of 1 k
Ω
in parallel with C29 of 4.7 µF, the
voltage and current phases are theoretically 45 degrees apart.
Figure 15. STPMS2L power metering schematic diagram
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STPMS2 power metering
R26
1K
GND
GND
GND
GND
C26
100nF
GND
GND
R27
1K
GND
R+jX Load
current
shunt
external generator input: pins 1 and 3
voltage of complex load: pins 2 and 3
shunt voltage : pins 1 and 2
VDD
VC
C
1
VD
DAC
2
VD
DA
3
VB
G
4
DATn
16
DAT
15
CLK
14
MS3
13
MS
2
12
MS
1
11
MS
0
10
VD
DAV
9
VIP
8
VIN
7
CIP
6
CIN
5
GN
D
17
A
V
Exposed
pad GND
U3
STPMS2L-PUR
3
2
1
CN4
GND
C2
9
4.7uF
C27
1uF
C2
2
1uF
C24
1uF
