MCP3909-I/SS Microchip Technology, MCP3909-I/SS Datasheet - Page 18

• 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

MCP3909 / dsPIC33F 3-Phase Energy Meter Reference Design
2.2
DS51723A-page 18
ANALOG FRONT END CIRCUITRY
For safety, current transformers are used between the voltage and current input signals
and the measurement module to isolate it from the 3-phase power supply.
The transformer used for the voltage path is a 1:1 transformer, SPT204B from Beijing
Singure Measurement & Control Technology Co., with non-linearity less than 0.1%, and
rated input/output current of 2 mA/2 mA.
The transformer used on the current side is a SPT254FK, from Yhehua Shanghai, with
rated input /output current of 20A/2 mA, non-linearity less than 0.1%, and linear range
of 0-20 A. See Appendix B. “Bill Of Materials (BOM)” for more information on the
input circuitry.
Using phase A as an example for the voltage signal path, a 150 kΩ (R
before the CT to transform the signal to an appropriate current. After the CT, burden
resistors R
age signal for the MCP3909 device to sample. Signals are coupled into the MCP3909
device's signal input port via R
quency signals.
Using phase A as an example for the current signal path, transformation of the current
signal is similar to that of the voltage signal. The burden resistors R
R
channel after considering the following 3 factors:
• The MCP3909 device's differential voltage input range: 1V for voltage channel
• Maximum current/voltage for the meter: rated current of 5A, maximum current of
• Transformer ratio for the current and voltage transformer.
A non-isolated voltage input circuit is included. In practice, a voltage divider network of
resistors is often used for sampling AC voltage input. This measuring method is
therefore included in the hardware design. In Figure 2-2, voltage divider resistors R
R
FIGURE 2-2:
116
4
and 0.705V for current channel
20A, and maximum voltage of 300V)
, and sampling resistor R
/R
CURRENT
VOLTAGE
117
VOLTAGE (Non-Isolated Option)
PA
N
PA
N
are chosen to be 20Ω for the current channel and 100Ω for the voltage
125
150 kΩ
CTA-1
CTA-2
and R
R
1
499 kΩ
R
4
126
Input Signal Conditioning Circuit (Phase A).
SPT204B
SCT220B
T103
T1
are needed to transform the current signal to a differential volt-
499 kΩ
R
1
3
construct a network for sampling AC voltage.
110
R
R
R
R
117
126
116
125
and R
1 kΩ
R
1
100 Ω
20 Ω
100 Ω
20 Ω
111
Jumper
. C
111
33 nF
C
3
R
R
R
and C
R
1.0 kΩ
109
1.0 kΩ
111
1.0 kΩ
1.0 kΩ
108
110
112
1 nF
1 nF
1 nF
C
1 nF
C
C
C
© 2009 Microchip Technology Inc.
are used to filter high-fre-
109
111
110
112
125
1
CH0-
CH0+
CH1+
) resistor is used
CH1+
MCP3909
/R
126
and
3
,