MCP3906A-I/SS Microchip Technology, MCP3906A-I/SS Datasheet - Page 15

• Manufacturer Part Number: MCP3906A-I/SS
• Description: IC POWER METERING-1 PHASE 24SSOP
• Manufacturer: Microchip Technology

Specifications of MCP3906A-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
• Brief Features: Active Real Power Pulse Output, Ultra Low Drift
• Supply Voltage Range: 4.5V To 5.5V
• Operating Temperature Range: -40°C To +85°C
• Digital Ic Case Style: SSOP
• No. Of Pins: 24
• Svhc: No
• Mounting Style: SMD/SMT
• Ic Function: Single Phase Energy Metering
• Rohs Compliant: Yes
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant
• For Use With: MCP3905RD-PM1 - REFERENCE DESIGN FOR MCP3905MCP3905EV - BOARD DEMO FOR MCP3905
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

The multiplier output gives the product of the two high-
pass filtered channels, corresponding to 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 contain-
ing 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.
4.6
The MCP3905A/05L/06A low-pass filter is a first-order
IIR filter that extracts the active real-power information
(DC component) from the instantaneous power signal.
The magnitude response of this filter is detailed in
Figure
signal has harmonic content (coming from the 2ω
components of the inputs), and since the filter is not
ideal, there will be some ripple at the output of the low-
pass filter at the harmonics of the line frequency.
The cut-off frequency of the filter (8.9 Hz) has been
chosen to have sufficient rejection for commonly-used
line frequencies (50 Hz and 60 Hz). With a standard
input clock (MCLK = 3.58 MHz) and a 50 Hz line
frequency, the rejection of the 2ω component (100 Hz)
will be more than 20 dB. This equates to a 2ω
component containing 10 times less power than the
main DC component (i.e., the average active real
power).
FIGURE 4-5:
(MCLK = 3.58 MHz).
The output of the low-pass filter is accumulated in the
digital-to-frequency converter. This accumulation is
compared to a different digital threshold for F
and HF
sured by the part. Every time the digital threshold on
F
pulse (See Section 4.7 “F
Frequencies”).
© 2006 Microchip Technology Inc.
OUT0/1
-10
-15
-20
-25
-30
-35
-40
4-5. Due to the fact that the instantaneous power
-5
OUT
0
or HF
0.1
Low-Pass Filter and DTF
Converter
, representing a quantity of real energy mea-
OUT
1
is crossed, the part will output a
LPF Magnitude Response
Frequency (Hz)
OUT0/1
10
and HF
100
OUT
Output
1000
OUT0/1
The equivalent quantity of real energy required to
output a pulse is much larger for the F
than the HF
for the F
integration period acts as another low-pass filter so that
the output ripple due to the 2ω components is minimal.
However, these components are not totally removed,
since realized low-pass filters are never ideal. This will
create a small jitter in the output frequency. Averaging
the output pulses with a counter or a MCU in the
application will then remove the small sinusoidal
content of the output frequency and filter out the
remaining 2ω ripple.
HF
due to its instantaneous power content. The shorter
integration period of HF
component be given more attention. Since a sinusoidal
signal average is zero, averaging the HF
steady-state conditions will give the proper real energy
value.
4.7
The thresholds for the accumulated energy are
different for F
different transfer functions). The F
output frequencies are quite low in order to allow
superior integration time (see Section 4.6 “Low-Pass
Filter and DTF Converter”). The F
frequency can be calculated with the following
equation:
EQUATION 4-1:
For a given DC input V, the DC and RMS values are
equivalent. For a given AC input signal with peak-to-
peak amplitude of V, the equivalent RMS value is
V/sqrt(2), assuming purely sinusoidal signals. Note
that since the real power is the product of two RMS
inputs, the output frequencies of AC signals are half of
the DC inputs ones, again assuming purely sinusoidal
AC signals. The constant F
and F
output frequencies for the different logic settings.
Where:
MCP3905A/05L/06A
OUT
V
V
G is the PGA gain on Channel 0 (current channel)
F
V
OUT1
0
1
C
REF
is intended to be used for calibration purposes
is the RMS differential voltage on Channel 0
is the RMS differential voltage on Channel 1
is the frequency constant selected
F
Frequencies
F
OUT0/1
OUT
OUT0/1
is the voltage reference
OUT
digital settings.
(
. This is such that the integration period
OUT0/1
Hz
outputs is much larger. This larger
)
and HF
=
8.06 V
---------------------------------------------------------- -
F
OUTPUT EQUATION
and HF
OUT
OUT
×
OUT
C
Table 4-3
FREQUENCY
(
0
V
depends on the F
demands that the 2ω
×
OUT
REF
V
Output
1
)
×
DS22011A-page 15
2
(i.e., they have
G
OUT0/1
shows F
OUT0/1
OUT0/1
×
OUT
F
C
signal in
allowed
outputs
output
OUT0/1
OUT0