MCP3909 datasheet(33/44 Pages) MICROCHIP

33 / 44 page

DS22025B-page 33

MCP3909

6.0

APPLICATIONS INFORMATION

The following application figures represent meter

designs using the MCP3909 device. Some of these

applications ideas are available as fully function meter

reference designs and demo boards. For complete

schematic and for fully function meter designs, visit

Microchip’s web page for demo board and reference

design availability.

6.1

Performing RMS, Apparent Power,

and Active Power using MCP3909

Waveform data

Figure 6-1

represents

power

calculations

from

waveform data based on a PIC MCU and MCP3909

device. The PIC MCU accomplishes the following

energy meter calculation outputs per phase, per line

cycle:

- RMS Current

-RMS Voltage

- Active Power

- Apparent Power

Output registers for the power quantities and

calibration registers for phase, offset, gain, and LSB

adjustment are available through a serial interface to

the PIC microcontroller. See Microchip’s web page for

firmware solution and demo board.

The example signal flow here shows 4 output power

quantities and 6 calibration registers. For a 60 Hz

design that is using 128 samples per line cycle for the

power calculation the MCP3909 would have a new

data

ready

pulse

every

130 µs.

The

SPI

communication to gather 16-bits x 2 channels at

10 MHz is approximately 3.2 µs, leaving ~125 µs for

the power calculations before the next sample is ready.

FIGURE 6-1:

Power Calculations from Waveform sampling using PIC MCU. Register names shown

are used on MCP3909 Energy Meter Reference Design.

PHA_W_OFF:32

PHA_W_GAIN:16

PHA_DELAY:8

PHA_V_RMS_OFF:16

PHA_VA_GAIN:16

ADC

CURRENT

VOLTAGE

Active Power

RMS Current

RMS Voltage

Apparent Power

MCP3909

PHA_I_RMS_OFF:16

PIC Microcontroller

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