MCP3909RD-3PH1 Microchip Technology, MCP3909RD-3PH1 Datasheet - Page 16

• Manufacturer Part Number: MCP3909RD-3PH1
• Description: REF DESIGN MCP3909 3PH ENGY MTR
• Manufacturer: Microchip Technology

Specifications of MCP3909RD-3PH1

• Main Purpose: Power Management, Energy/Power Meter
• Embedded: No
• Utilized Ic / Part: MCP3909, PIC18F2520, PIC18F4550
• Primary Attributes: 3-Ph, 220 VAC, In Case, LCD, USB, GUI
• Secondary Attributes: Opto-Isolated Interface for Safety
• Operating Voltage: 220 V
• Operating Current: 5 A
• Description/function: Energy Meter
• For Use With/related Products: MCP3909
• Lead Free Status / RoHS Status: Not applicable / Not applicable

MCP3909 3-Phase Energy Meter Reference Design
2.2
FIGURE 2-2:
DS51643B-page 12
SDO DR
IRQ
IRQ
50 (or 60 Hz)
CLOCK GENERATION CIRCUIT AND PLL
Phase A,B,C I & V Data
Option 1
Phase A || B || C
PLL Circuit
x 32768
To achieve simultaneous sampling across the three phases, all 3 MCP3909 devices
use the same clock source. In this configuration, the six delta-sigma ADCs are being
clocked simultaneously. The source used in this reference design can either be the
output of the CCP2 timer on the PIC18F2520 or the output of the phase lock loop (PLL)
circuit locked to the line frequency. In either situation, the target number of samples per
line cycle is 128. The PLL is designed to have a multiplier of 32768 resulting in a MCLK
for the MCP3909 devices that results in exactly 128 samples per line cycle. For lower
cost meters, the PLL circuit can be avoided and instead, the CCP2 timer output can
provide the appropriate MCLK frequency from a PIC oscillator clock of 39.3216 MHz.
This will generate an integer number of samples for either 50 Hz or 60 Hz line
frequencies. R31 and R34 select the source of the MCLK signal for the MCP3909s-PLL
or CCP2 / 32768..
Timing Structure of PIC18F2520 Interrupts and Calculations.
x 6 ADCs
16 bits
t
MCP3909
LINE_CYC
t
SAMPLE
1.96606 MHz (60 Hz)
t
1.6384 MHz (50 Hz)
SAMPLE
R31
MCP3909
R34
MCLK input
MCP3909
IRQ
50 Hz or 60 Hz
39.3216 MHz
PIC MCU
CCP2 / 32768
DR Pulse
X1
© 2008 Microchip Technology Inc.
Option 2
DR
To PIC18F2520
IRQ