MCP3909-I/SS Microchip Technology, MCP3909-I/SS Datasheet - Page 21

• 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

If an external voltage reference source is connected to
the REFIN/OUT pin, the external voltage will be used
as the reference for both current and voltage channel
ADCs. The voltage across the source resistor will then
be the difference between the internal and external
voltage. The allowed input range for the external
voltage source goes from 2.2V to 2.6V for accurate
measurement error. A V
will cause additional heating and power consumption
due to the source resistor, which might affect
measurement error.
4.5
The MCP3909 contains an internal POR circuit that
monitors analog supply voltage AV
This circuit ensures correct device startup at system
power-up and system power-down events. The POR
circuit has built-in hysteresis and a timer to give a high
degree of immunity to potential ripple and noise on the
power supplies, allowing proper settling of the power
supply during power-up. A 0.1 µF decoupling capacitor
should be mounted as close as possible to the
AV
(see Section 6.0 “Applications Information”).
The threshold voltage is typically set at 4V, with a
tolerance of about ±5%. If the supply voltage falls below
this threshold, the MCP3909 will be held in a Reset
condition (equivalent to applying logic ‘0’ on the MCLR
pin). The typical hysteresis value is approximately
200 mV in order to prevent glitches on the power sup-
ply.
Once a power-up event has occurred, an internal timer
prevents the part from outputting any pulse for
approximately 1s (with MCLK = 3.58 MHz), thereby
preventing potential metastability due to intermittent
resets caused by an unsettled regulated power supply.
Figure 4-3
power-up and a power-down event in the typical
conditions.
FIGURE 4-3:
© 2009 Microchip Technology Inc.
DEVICE
MODE
DD
AV
4.2V
5V
4V
0V
DD
pin, providing additional transient immunity
Power-On Reset (POR)
RESET
illustrates the different conditions for a
PULSE
OUT
NO
1s
Power-on Reset Operation.
REF
OPERATION
PROPER
value outside of this range
DD
during operation.
RESET
Time
4.6
The active real-power value is extracted from the DC
instantaneous power. Therefore, any DC offset
component present on Channel 0 and Channel 1
affects the DC component of the instantaneous power
and will cause the real-power calculation to be
erroneous. In order to remove DC offset components
from the instantaneous power signal, a high-pass filter
has been introduced on each channel. Since the
high-pass filtering introduces phase delay, identical
high-pass filters are implemented on both channels.
The filters are clocked by the same digital signal,
ensuring a phase difference between the two channels
of less than one MCLK period. Under typical conditions
(MCLK = 3.58 MHz), this phase difference is less than
0.005°, with a line frequency of 50 Hz. The cut-off
frequency of the filter (4.45 Hz) has been chosen to
induce minimal gain error at typical line frequencies,
allowing sufficient settling time for the desired
applications. The two high-pass filters can be disabled
by applying logic ‘0’ to the HPF pin.
FIGURE 4-4:
(MCLK = 3.58 MHz).
The multiplier output gives the product of the two
high-pass
instantaneous real power. Multiplying two sine wave
signals by the same ω frequency gives a DC
component and a 2ω component. The instantaneous
power signal contains the real power of its DC
component, while also containing 2ω components
coming from the line frequency multiplication. These
2ω components come for the line frequency (and its
harmonics) and must be removed in order to extract the
real-power information. This is accomplished using the
low-pass filter and DTF converter.
-10
-15
-20
-25
-30
-35
-40
-5
0
0.1
High-Pass Filters and Multiplier
filtered
1
channels,
HPF Magnitude Response
Frequency (Hz)
10
MCP3909
corresponding
DS22025B-page 21
100
1000
to