AN_6612_007
78M6612 Hardware Design Guidelines
Rev 2
3
2.2 3.3 VDC Supply (V3P3) and System Connection
The 78M6612 requires a single 3.3 VDC supply. The 3.3 VDC (V3P3) also represents the reference
potential for the 78M6612. The basic connections for a shunt-based system are represented in Figure 1.
Shunt
NEUTRAL
LINE
VA
VB
750
1M
1M
1000pF
IA
1000pF
Unused
Input(s)
LOAD
750
78M6612
1M
1M
EARTH
V3P3
750
1000pF
0.1uF
0.1uF
0.1uF
Figure 1: Basic Connection Diagram on Shunt-Based Systems
The analog inputs to the 78M6612 are used as follows:
•
VA input is used to measure the line voltage.
•
IA input is used to measure the load current.
•
VB input is used to flag a Line/Neutral polarity reversal. If this feature is not desired, terminate A2 to
V3P3 through a resistor-capacitor filter.
•
IB is in this case not used. It is terminated to V3P3 through a resistor-capacitor filter.
Notes:
•
The values used for the anti-aliasing filters are 750
Ω
and 0.1 µF. The filters have in this case a cutoff
frequency of about 2.1 kHz. Since the sample rate of the ADC converter may vary depending on the
different firmware configurations, a different value may be required. To tune the filter, it is
recommended to keep the 750
Ω
resistor unchanged and modify the value of the capacitor.
Do not tie the ground of the 78M6612 directly to earth ground. See the
section.
