MCP3905-I/SS Microchip Technology, MCP3905-I/SS Datasheet - Page 11

• Manufacturer Part Number: MCP3905-I/SS
• Description: IC ENERGY METER 24-SSOP
• Manufacturer: Microchip Technology

Specifications of MCP3905-I/SS

• Input Impedance: 390 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.85V
• Current - Supply: 2.7mA
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Package / Case: 24-SSOP (0.200", 5.30mm Width)
• Meter Type: Single Phase
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

4.0
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.
FIGURE 4-1:
© 2007 Microchip Technology Inc.
CH0+
CH0-
CH1+
CH1-
Frequency
DEVICE OVERVIEW
Content
Line Frequency
with System
+
–
Input Signal
+
–
PGA
Offset and
Simplified MCP3905/06 Block Diagram with Frequency Contents.
0
ANALOG
ΔΣ
ΔΣ
ADC
ADC
Code Contains
DIGITAL
ADC Output
System and
ADC Offset
0
HPF
HPF
DC Offset
Removed
0
by HPF
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 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
F
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 HF
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
“F
OUT0
OUT0/1
Instantaneous
and F
0
Power
and HF
LPF
OUT1
OUT
outputs are designed to drive electro-
MCP3905/06
Active (Real) Power
Instantaneous
Output Frequencies”).
MCP3905/06
0
..
0
1
DTF
0
1
...
DS21948D-page 11
F
HF
F
OUT0
OUT1
OUT
OUT
output