MCP3909RD-3PH3 Microchip Technology, MCP3909RD-3PH3 Datasheet - Page 17

• 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

2.1
© 2009 Microchip Technology Inc.
OVERVIEW
Figure 2-1 is the basic hardware block diagram of the MCP3909 / dsPIC33F 3-Phase
Energy Meter Reference Design. The hardware includes the dsPIC33F and ICD 2
interface, analog signal conditioning for 3-phase voltage/current inputs and current
using the MCP3909 Energy Meter IC, neutral current measurement using external
op-amp on-board dsPIC33F ADC, UART interface to PC, ICD2 interface for MCU
programming, and power supply circuits. Note there are two PCBs comprising this
energy meter, the power supply PCB, and the MCU/AFE PCB. Refer to Appendix
A. “Schematics and Layouts” for more information.
Three-phase voltage and current signals are connected to the meter through
transformers, and connected to the MCP3909 A/D converter through a simple signal
conditioning circuit. The MCP3909 device samples the signal and performs the
analog-to-digital conversion (ADC). The MCP3909 device sends the digital conversion
results to the dsPIC device via the SPI interface.
The MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design uses a quasi-syn-
chronous sampling algorithm via the dsPIC33F, therefore eliminating the need for
voltage zero-crossing detect and clock generating circuit, which are otherwise needed
in a synchronous sampling algorithm. The clock of the MCP3909 device is an active
external 3.2768 MHz crystal.
.
FIGURE 2-1:
Chapter 2. Hardware Description
Phase A
Phase A
Phase B
Phase B
Phase C
Phase C
Neutral
line CT
PT
CT
PT
CT
PT
CT
ENERGY METER REFERENCE DESIGN
Op Amp
Hardware Block Diagram.
MCP3909 / DSPIC33F 3-PHASE
CLK
Control
3.2768
Gain
MHz
SPI
Power Supply
SPI
+5V
I/O
dsPIC33FJ64GP206
ADC
UART
Power Supply
+3.3V
DS51723A-page 17
RS232