MCP3909-I/SS Microchip Technology, MCP3909-I/SS Datasheet - Page 24

• Manufacturer Part Number: MCP3909-I/SS
• Description: IC POWER METERING-1 PHASE 24SSOP
• Manufacturer: Microchip Technology

Specifications of MCP3909-I/SS

• Package / Case: 24-SSOP (0.200", 5.30mm Width)
• Input Impedance: 390 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.85V
• Current - Supply: 2.3mA
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Meter Type: Single Phase
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Supply Voltage Range: 4.5V To 5.5V
• Digital Ic Case Style: SSOP
• No. Of Pins: 24
• Interface Type: Serial, SPI
• Supply Voltage Max: 5.5V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: MCP3909EV-MCU16 - EVALUATION BOARD FOR MCP3909MCP3909RD-3PH1 - REF DESIGN MCP3909 3PH ENGY MTR
• Lead Free Status / Rohs Status: 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