MCP3909-I/SS Microchip Technology, MCP3909-I/SS Datasheet - Page 19

• 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.
2.2.1
The high precision class 0.2S requirement for the energy meter makes it crucial to
select proper burden resistors for the output of the current transformers.
Metal film resistors with low inherent noise and temperature coefficient are ideal. Given
that the secondary current of the CT is I, then the input voltage of the MCP3909 device
is U = IR, where R is the resistance of R
If the temperature varies by ΔT, and the temperature coefficient of sampling resistor R
is β ppm/°C, then the output voltage is:
EQUATION 2-1:
The voltage variation is:
EQUATION 2-2:
This relationship shows that the output voltage variation caused by temperature
variation is in proportion to the temperature coefficient of the burden resistor.
In addition, a smaller temperature coefficient benefits meter start stabilization after
startup. It takes a longer time for resistors with larger temperature coefficient to
stabilize. Therefore, accurate measurements would require a longer wait after
power-up. This affects the efficiency, or speed of meter calibration.
Burden Resistor Temperature Coefficient
ΔU
=
U' U
–
U'
=
=
I
×
I R
(
ΔT β
125
+
×
Δ
and R
Hardware Description
T
×
×
R
β
126
×
=
R
U
)
(Using Phase A as an example).
×
ΔT
×
β
DS51723A-page 19