MCP3909-I/SS Microchip Technology, MCP3909-I/SS Datasheet - Page 99

• Manufacturer Part Number: MCP3909-I/SS
• Description: IC POWER METERING-1 PHASE 24SSOP
• Manufacturer: Microchip Technology

Specifications of MCP3909-I/SS

• Package / Case: 24-SSOP (0.200", 5.30mm Width)
• Input Impedance: 390 KOhm
• Measurement Error: 0.1%
• Voltage - I/o High: 2.4V
• Voltage - I/o Low: 0.85V
• Current - Supply: 2.3mA
• Voltage - Supply: 4.5 V ~ 5.5 V
• Operating Temperature: -40°C ~ 85°C
• Mounting Type: Surface Mount
• Meter Type: Single Phase
• Operating Temperature Range: - 40 C to + 85 C
• Mounting Style: SMD/SMT
• Supply Voltage Range: 4.5V To 5.5V
• Digital Ic Case Style: SSOP
• No. Of Pins: 24
• Interface Type: Serial, SPI
• Supply Voltage Max: 5.5V
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: MCP3909EV-MCU16 - EVALUATION BOARD FOR MCP3909MCP3909RD-3PH1 - REF DESIGN MCP3909 3PH ENGY MTR
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

© 2009 Microchip Technology Inc.
Given that the phase lag between the input voltage and current is φ, after PT and CT,
the actual measured active power is P', reactive power is Q'. RMS current is I, RMS
voltage is V, input apparent power is S, actual input active power is P and reactive
power is Q, then Figure C-11 can be drawn based on the principles of power triangle.
EQUATION C-66:
EQUATION C-67:
From the above 2 equations, we have:
EQUATION C-68:
EQUATION C-69:
Where:
EQUATION C-70:
EQUATION C-71:
By setting up certain input conditions, Δϕ can be measured, and then k
calculated.
In this design, we use an input of 0.5L for calibration. With this condition, Δϕ can be
calculated using the difference between the meaured and the actual input value of
active power. For accurate calculations, the user may also use the difference between
the measured cumulative energy and the actual cumulative energy to calculate the
difference.
EQUATION C-72:
Where err is the error rate of the energy measurement, which results from calculating
the error between the actual energy measured by a standard meter and the energy
measured by the dsPIC devices. The error can be obtained from the output of the meter
calibration workbench.
EQUATION C-73:
Δϕ
P'
Q'
=
=
=
a
cos
V I
V I
⋅ ⋅
⋅ ⋅
⎛
⎝
---------- -
2 P
err
P'
cos
⋅
sin
⎞
⎠
=
Power Calculation Theory
P
(
(
Q
φ
φ
–
k
k
P' P
------------- -
=
+
+
=
π
-- -
3
1
1
P
–
Δϕ
Δϕ
=
k
=
=
k
1
1
P'
Q' k
cos
)
)
a
sin
=
cos
+
=
=
–
Δ
Δϕ
Δ
------ -
k
ϕ
P
P
Q
⎛
⎝
2
2
P
(
Q'
P'
cos
cos
0.5
×
100
Δϕ
Δϕ
⋅
(
1
–
–
+
Q
P
err
sin
sin
)
Δϕ
Δϕ
)
–
π
-- -
3
⎞
⎠
DS51723A-page 99
1
and k
2
can be