MCP3906 datasheet(11/26 Pages) MICROCHIP

11 / 26 page

DS21948C-page 11

MCP3905/06

4.0

DEVICE OVERVIEW

The MCP3905/06 is an energy-metering IC that

supplies a frequency output proportional to active (real)

power, and higher frequency output proportional to the

instantaneous power for meter calibration. Both chan-

nels use 16-bit, second-order, delta-sigma ADCs that

oversample the input at a frequency equal to MCLK/4,

allowing for wide dynamic range input signals. A

Programmable Gain Amplifier (PGA) increases the

usable range on the current input channel (Channel 0).

The calculation of the active (real) power, as well as the

filtering associated with this calculation, is performed in

the digital domain, ensuring better stability and drift

performance. Figure 4-1 represents the simplified

block diagram of the MCP3905/06, detailing its main

signal-processing blocks.

Two digital high-pass filters cancel the system offset on

both channels such that the real-power calculation

does not include any circuit or system offset. After

being high-pass filtered, the voltage and current signals

are multiplied to give the instantaneous power signal.

This signal does not contain the DC offset components,

such that the averaging technique can be efficiently

used to give the desired active (real) power output.

The instantaneous power signal contains the real-

power information; it is the DC component of the

instantaneous power. The averaging technique can be

used with both sinusoidal and non-sinusoidal wave-

forms,

well

for

all

power

factors.

The

instantaneous power is thus low-pass filtered in order

to produce the instantaneous real-power signal.

A DTF converter accumulates the instantaneous active

(real) power information to produce output pulses with a

frequency proportional to the average active (real)

power. The low-frequency pulses presented at the

FOUT0 and FOUT1 outputs are designed to drive electro-

mechanical counters and two-phase stepper motors

displaying the real-power energy consumed. Each pulse

corresponds to a fixed quantity of real energy, selected

by the F2, F1 and F0 logic settings. The HFOUT output

has a higher frequency setting and lower integration

period such that it can represent the instantaneous

active (real) power signal. Due to the shorter accumula-

tion time, it enables the user to proceed to faster calibra-

tion under steady load conditions (refer to Section 4.7

“FOUT0/1 and HFOUT Output Frequencies”).

FIGURE 4-1:

Simplified MCP3905/06 Block Diagram with Frequency Contents.

HPF

...

DTF

–

ADC

–

PGA

LPF

HPF

CH0+

CH0-

CH1+

CH1-

ADC

FOUT0

FOUT1

HFOUT

MCP3905/06

Frequency

Content

ΔΣ

ADC Output

Code Contains

System and

ADC Offset

DC Offset

Removed

by HPF

Instantaneous

Power

ANALOG

DIGITAL

Instantaneous

Active (Real) Power

Input Signal

with System

Offset and

Line Frequency

MCP3906 Datasheet(PDF) 11 Page - Microchip Technology

MCP3906 Datasheet(HTML) 11 Page - Microchip Technology

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26

Datasheet Download

Link URL