MCP3903-I/SS Microchip Technology, MCP3903-I/SS Datasheet - Page 23

• Manufacturer Part Number: MCP3903-I/SS
• Description: IC AFE 24BIT 64KSPS 28SSOP
• Manufacturer: Microchip Technology
• Series: -r

Specifications of MCP3903-I/SS

• Featured Product: MCP3903 Six Channel ΔΣ A/D Converter
• Number Of Bits: 24
• Number Of Channels: 6
• Power (watts): -
• Voltage - Supply, Analog: 4.5 V ~ 5.5 V
• Voltage - Supply, Digital: 2.7 V ~ 3.6 V
• Package / Case: 28-SSOP (0.209", 5.30mm Width)
• Lead Free Status / Rohs Status: Lead free / RoHS Compliant

5.0
5.1
The MCP3903 analog inputs can be connected directly
to current and voltage transducers (such as shunts,
current transformers, or Rogowski coils). Each input
pin is protected by specialized ESD structures that are
certified to pass 5 kV HBM and 500V MM contact
charge. These structures allow bipolar ±6V continuous
voltage with respect to AGND, to be present at their
inputs without the risk of permanent damage.
All channels have fully differential voltage inputs for
better noise performance. The absolute voltage at each
pin relative to AGND should be maintained in the ±1V
range during operation in order to ensure the specified
ADC accuracy. The Common-Mode signals should be
adapted to respect both the previous conditions and
the
performance, the Common-Mode signals should be
maintained to AGND.
5.2
The six Programmable Gain Amplifiers (PGAs) reside
at the front-end of each Delta-Sigma ADC. They have
two functions: translate the common-mode of the input
from AGND to an internal level between AGND and
A
translation of the common mode does not change the
differential signal but recenters the common-mode so
that the input signal can be properly amplified.
The PGA block can be used to amplify very low signals,
but the differential input range of the delta-sigma
modulator must not be exceeded. The PGA is
controlled by the PGA_CHn<2:0> bits in the GAIN
register. The following table represents the gain
settings for the PGA:
TABLE 5-1:
© 2011 Microchip Technology Inc.
VDD
PGA_CHn<2:0>
0
0
0
0
1
1
, and amplify the input differential signal. The
differential
Gain
DEVICE OVERVIEW
Analog Inputs (CHn+/-)
Programmable Gain Amplifiers
(PGA)
0
0
1
1
0
0
0
1
0
1
0
1
PGA CONFIGURATION
SETTING
input
Gain
(V/V)
16
32
1
2
4
8
voltage
Gain
(dB)
12
18
24
30
0
6
range.
±0.5
±0.25
±0.125
±0.0625
±0.03125
±0.015625
V
IN
For
Range
(V)
best
5.3
5.3.1
All ADCs are identical in the MCP3903 and they
include a second-order modulator with a multi-bit DAC
architecture (see
ADC composed of 4 comparators with equally spaced
thresholds and a thermometer output coding. The
proprietary 5-level architecture ensures minimum
quantization noise at the outputs of the modulators
without disturbing linearity or inducing additional
distortion. The sampling frequency is DMCLK (typically
1 MHz with MCLK=4 MHz) so the modulator outputs
are refreshed at a DMCLK rate. The modulator outputs
are available in the MOD register.
Each modulator also includes a dithering algorithm that
can be enabled through the DITHER<5:0> bits in the
configuration register. This dithering process improves
THD and SFDR (for high OSR settings) while
increasing slightly the noise floor of the ADCs. For
power metering applications and applications that are
distortion-sensitive, it is recommended to keep
DITHER enabled for all ADCs. In the case of power
metering applications, THD and SFDR are critical
specifications to optimize SNR (noise floor). This is not
really problematic due to large averaging factor at the
output of the ADCs, therefore even for low OSR
settings, the dithering algorithm will show a positive
impact on the performance of the application.
Figure 5-1
Delta-Sigma ADC present on MCP3903.
FIGURE 5-1:
Block Diagram.
Differential
Voltage Input
Delta-Sigma Modulator
represents a simplified block diagram of the
ARCHITECTURE
MCP3903 Sigma-Delta Modulator
Figure
Loop
Filter
Integrator
Second-
Order
Simplified Delta-Sigma ADC
5-1). The quantizer is a flash
MCP3903
Flash ADC
Quantizer
DAC
DS25048B-page 23
5-level
Bitstream
Output