MCP3906 Microchip Technology, MCP3906 Datasheet - Page 16

• Manufacturer Part Number: MCP3906
• Description: (MCP3905 / MCP3906) Energy-Metering ICs
• Manufacturer: Microchip Technology

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MCP3905/06
4.1
The MCP3905/06 analog inputs can be connected
directly to the current and voltage transducers (such as
shunts or current transformers). Each input pin is
protected by specialized Electrostatic Discharge (ESD)
structures that are certified to pass 5 kV HBM and
500V MM contact charge. These structures also allow
up to ±6V continuous voltage to be present at their
inputs without the risk of permanent damage.
Both channels have fully differential voltage inputs for
better noise performance. The absolute voltage at each
pin relative to A
range during operation in order to ensure the measure-
ment error performance. The common mode signals
should be adapted to respect both the previous
conditions and the differential input voltage range. For
best performance, the common mode signals should
be referenced to A
The current channel comprises a PGA on the front-end
to allow for smaller signals to be measured without
additional
differential voltage specified on Channel 0 is equal to
±470 mV/Gain (see
voltage specified on Channel 1 is equal to ±660 mV.
TABLE 4-1:
TABLE 4-2:
4.2
The ADCs used in the MCP3905/06 for both current
and voltage channel measurements are delta-sigma
ADCs. They comprise a second-order, delta-sigma
modulator using a multi-bit DAC and a third-order SINC
filter. The delta-sigma architecture is very appropriate
for the applications targeted by the MCP3905, because
it is a waveform-oriented converter architecture that
can offer both high linearity and low distortion
performance throughout a wide input dynamic range. It
also creates minimal requirements for the anti-aliasing
filter design. The multi-bit architecture used in the ADC
minimizes quantization noise at the output of the
converters without disturbing the linearity.
DS21948E-page 16
G1
G1
0
0
1
1
0
0
1
1
Analog Inputs
16-Bit Delta-Sigma ADCs
signal
G0
G0
0
1
0
1
0
1
0
1
GND
MCP3905 GAIN SELECTIONS
MCP3906 GAIN SELECTIONS
GND
should be maintained in the ±1V
Table
conditioning.
CH0 Gain
CH0 Gain
.
16
32
16
1
2
8
1
8
4-1). The maximum peak
The
CH0 Voltage
CH0 Voltage
Maximum
Maximum
±470 mV
±235 mV
±470 mV
±60 mV
±30 mV
±15 mV
±60 mV
±30 mV
maximum
Both ADCs have a 16-bit resolution, allowing wide input
dynamic range sensing. The oversampling ratio of both
converters is 64. Both converters are continuously
converting during normal operation. When the MCLR
pin is low, both converters will be in Reset and output
code 0x0000h. If the voltage at the inputs of the ADC is
larger than the specified range, the linearity is no longer
specified. However, the converters will continue to
produce output codes until their saturation point is
reached. The DC saturation point is around 700 mV for
Channel 0 and 1V for Channel 1, using internal voltage
reference.
The clocking signals for the ADCs are equally
distributed between the two channels in order to
minimize phase delays to less than 1 MCLK period
(see Section 3.2 “High-Pass Filter Input Logic Pin
(HPF)”). The SINC filters main notch is positioned at
MCLK/256 (14 kHz with MCLK = 3.58 MHz), allowing
the user to be able to measure wide harmonic content
on either channel. The magnitude response of the
SINC filter is shown in
FIGURE 4-2:
Response (MCLK = 3.58 MHz).
4.3
The MCP3905/06 contains an internal voltage
reference source specially designed to minimize drift
over
reference voltage to both current and voltage channel
ADCs. The typical value of this voltage reference is
2.4V, ±100 mV. The internal reference has a very low
typical temperature coefficient of ±15 ppm/°C, allowing
the output frequencies to have minimal variation with
respect to temperature since they are proportional to
(1/V
REFIN/OUT is the output pin for the voltage reference.
Appropriate bypass capacitors must be connected to
the REFIN/OUT pin for proper operation (see
Section 5.0
voltage reference source impedance is typically 4 kΩ,
which enables this voltage reference to be overdriven
by an external voltage reference source.
REF
-100
-120
temperature.
-20
-40
-60
-80
)².
0
Ultra-Low Drift V
0
“Applications
5
This
SINC Filter Magnitude
Figure
10
Frequency (kHz)
© 2009 Microchip Technology Inc.
internal
15
4-2.
REF
Information”).
20
V
REF
25
supplies
30
The