MCP3909RD-3PH3 Microchip Technology, MCP3909RD-3PH3 Datasheet - Page 24

• Manufacturer Part Number: MCP3909RD-3PH3
• Description: REF DESIGN FOR MCP3909 W/18F2520
• Manufacturer: Microchip Technology

Specifications of MCP3909RD-3PH3

• Main Purpose: Power Management, Energy/Power Meter
• Utilized Ic / Part: MCP3909, PIC18F2520, PIC18F4550
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• Secondary Attributes: -
• Embedded: -
• Primary Attributes: -
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant, Lead free / RoHS Compliant

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design
.
FIGURE 2-5:
DS51723A-page 24
4.7 kΩ
4.7 kΩ
R
R
129
130
3.3V
2.4.3
Detection of neutral wire tampering is performed by the on-chip A/D of the dsPIC
device. The purpose of the detection is to prevent electricity theft, balance 3-phase
signals and detect electricity leakage. Since the precision is not critical, a dsPIC
on-chip A/D is sufficient.
Figure 2-5 shows the circuit for neutral current detection. The neutral input uses R
for sampling. To bias the AC signals to the A/D measurement range, a 3.3V power
supply is divided by R
MCP6002 device to output a boost voltage REV_V of 1.65V. The biased voltage is then
connected to the CT in series. The CT's sampling voltage is connected to Op-amp B of
the MCP6002 device via R
voltage, Current_N, for the current. Both Current_N and 1.65V V
sampled and measured by the dsPIC on-chip A/D.
Circuit of Neutral Line Detection.
Neutral Wire Input
T100 Secondary
U101_A
+
-
Neutral Current Detection
130
and R
127
470Ω
R
128
as emitter-follower output, generating the sampling
129
and connected to the emitter-follower of the
4.7 kΩ
R
127
U101_B
+
-
© 2009 Microchip Technology Inc.
REF
1.65V V
Current_N
signals are
REF
128