MCP3905L Microchip Technology, MCP3905L Datasheet - Page 12

• Manufacturer Part Number: MCP3905L
• Description: (MCP3905A / MCP3906A) Energy Metering ICs
• Manufacturer: Microchip Technology

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MCP3905A/05L/06A
4.0
The MCP3905A/05L/06A devices are energy metering
ICs that supply a frequency output proportional to
active (real) power, and higher frequency output pro-
portional to the instantaneous power for meter calibra-
tion. 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 chan-
nel (Channel 0). The calculation of the active power,
and the filtering associated with this calculation is per-
formed in the digital domain, ensuring better stability
and drift performance.
fied block diagram of the MCP3905A/05L/06A, detail-
ing 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:
DS22011A-page 12
CH0+
CH0-
CH1+
CH1-
Frequency
Content
DEVICE OVERVIEW
System Offset and
–
–
+
+
Input Signal with
PGA
Line Frequency
0
Figure 4-1
Simplified
ANALOG
represents the simpli-
MCP3905A/05L/06A
ADC
ADC
DIGITAL
ADC Output Code
Contains System
and ADC Offset
0
HPF
HPF
Removed by HPF
0
DC Offset
Block Diagram with Frequency Contents.
X
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, 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
less integration period such that it can represent the
instantaneous real-power signal. Due to the shorter
accumulation time, it enables the user to proceed to
faster calibration under steady load conditions (see
Section 4.7
Frequencies”).
Instantaneous
OUT
0
OUT0
Power
LPF
output has a higher frequency setting and
and F
“F
OUT0/1
OUT1
MCP3905
0
Instantaneous
MCP390X
© 2006 Microchip Technology Inc.
Real Power
outputs are designed to drive
..
0
and
1
DTF
0
1
...
HF
OUT
F
F
HF
OUT1
OUT0
Output
OUT