MCP3909-I/SP Microchip Technology, MCP3909-I/SP Datasheet - Page 16

• Manufacturer Part Number: MCP3909-I/SP
• Description: Power Meter with SPI and Active Power Pulse Output & Internal Oscillator., -40C to +85C, 28-SPDIP, TUBE
• Manufacturer: Microchip Technology

MCP3909
4.0
The MCP3909 is an energy metering IC that serves two
distinct functions that can operate simultaneously:
For the active power output, the device supplies a
frequency output proportional to active (real) power,
and higher frequency output proportional to the
instantaneous power for meter calibration.
For the waveform output, it can be used serially to
gather 16-bit voltage channel and current channel A/D
data, or 20-bit wide multiplier output data. Both
channels 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).
Figure 4-1
the MCP3909, 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-power output.
FIGURE 4-1:
DS22025A-page 16
- Active Power Pulse Output
- Waveform Output via SPI Interface
CH0+
CH0-
CH1+
CH1-
Frequency
Content
DEVICE OVERVIEW
represents the simplified block diagram of
+
+
System offset and
-
-
Input Signal with
PGA
line frequency
0
Active Power Signal Flow with Frequency Contents.
ANALOG
ADC
ADC
ADC Output code
DIGITAL
contains System
and ADC offset
0
HPF
HPF
removed by HPF
0
DC Offset
X
4.1
The instantaneous power signal contains the active-
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, as well as for all power factors. The
instantaneous power is thus low-pass filtered in order
to produce the instantaneous real-power signal.
A digital-to-frequency converter accumulates the
instantaneous active real power information to produce
output pulses with a frequency proportional to the
average real power. The low-frequency pulses present
at the F
electromechanical 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
HF
integration period such that it can represent the instanta-
neous real-power signal. Due to the shorter accumula-
tion time, it enables the user to proceed to faster
calibration
Section 4.8 “Active Power F
put Frequencies”).
OUT
INSTANTANEOUS
output has a higher frequency setting and less
0
OUT0
Active Power
POWER
LPF
under
and F
OUT1
steady
INSTANTANEOUS
MCP3909
REAL POWER
© 2006 Microchip Technology Inc.
0
outputs are designed to drive
..
0
DTF
1
OUT0/1
0
load
1
...
conditions
and HF
HF
F
F
OUT
OUT0
OUT1
OUT
Out-
(see