MCP3426 Datasheet, PDF (29/56 Pages) Maxim Integrated Products – 16-Bit, Multi-Channel Analog-to-Digital Converter with I2C Interface and On-Board Reference

6.0 BASIC APPLICATION
CONFIGURATION
The MCP3426/7/8 devices can be used for various
precision analog-to-digital converter applications.
These devices operate with very simple connections to
the application circuit. The following sections discuss
the examples of the device connections and
applications.
6.1 Connecting to the Application
Circuits
6.1.1
BYPASS CAPACITORS ON V_DD PIN
For an accurate measurement, the application circuit
needs a clean supply voltage and must block any noise
signal to the MCP3426/7/8 devices. Figure 6-1 shows
an example of using two bypass capacitors (a 10 µF
tantalum capacitor and a 0.1 µF ceramic capacitor) on
the V_DD line of the MCP3428. These capacitors are
helpful to filter out any high frequency noises on the
V_DD line and also provide the momentary bursts of
extra currents when the device needs from the supply.
These capacitors should be placed as close to the V_DD
pin as possible (within one inch). If the application
circuit has separate digital and analog power supplies,
the V_DD and V_SS of the MCP3426/7/8 devices should
reside on the analog plane.
6.1.2
CONNECTING TO I²C BUS USING
PULL-UP RESISTORS
The SCL and SDA pins of the MCP3426/7/8 are
open-drain configurations. These pins require a pull-up
resistor as shown in Figure 6-1. The value of these
pull-up resistors depends on the operating speed
(standard, fast, and high speed) and loading
capacitance of the I²C bus line. Higher value of pull-up
resistor consumes less power, but increases the signal
transition time (higher RC time constant) on the bus.
Therefore, it can limit the bus operating speed. The
lower value of resistor, on the other hand, consumes
higher power, but allows higher operating speed. If the
bus line has higher capacitance due to long bus line or
high number of devices connected to the bus, a smaller
pull-up resistor is needed to compensate the long RC
time constant. The pull-up resistor is typically chosen
between 5 kΩ and 10 kΩ ranges for standard and fast
modes, and less than 1 kΩ for high speed mode
depending on the presence of bus loading capacitance.
© 2009 Microchip Technology Inc.
MCP3426/7/8
6.1.3
I²C ADDRESS SELECTION PINS
(MCP3427 AND MCP3428)
The user can tie the Adr0 and Adr1 pins to V_SS, V_DD,
or left floating. See more details in Section 5.3.2
“Device Address Bits (A2, A1, A0) and Address
Selection Pins (MCP3427 and MCP3428)”.
Input
Signal 1
Input
Signal 2
C₁
MCP3428
1 CH1+
2 CH1-
3 _CH2+
4 CH2-
5 V_SS
6 V_DD
7 SDA
CH4- 14
CH4+ 13
CH3- 12
CH3+ 11
Adr1 10
Adr0 ⁹
SCL 8
Input
Signal 4
Input
Signal 3
I²C Address
Selection
Pins
C₂
TO MCU
(MASTER)
R_P
R_P
V_DD
Rp is the pull-up resistor:
5 kΩ - 10 kΩ for f_SCL = 100 kHz to 400 kHz
~700Ω for f_SCL = 3.45 MHz
C₁: 0.1 µF, Ceramic capacitor
C₂: 10 µF, Tantalum capacitor
FIGURE 6-1:
Typical Connection.
Figure 6-2 shows an example of multiple device
connections. The I²C bus loading capacitance
increases as the number of device connected to the I²C
bus line increases. The bus loading capacitance affects
on the bus operating speed. For example, the highest
bus operating speed for the 400 pF bus capacitance is
1.7 MHz, and 3.4 MHz for 100 pF. Therefore, the user
needs to consider the relationship between the
maximum operation speed versus. the number of I²C
devices that are connected to the I²C bus line.
Microcontroller
(PIC16F876)
SDA SCL
MCP3426
MCP3427
MCP3428
MCP4725
FIGURE 6-2:
Example of Multiple Device
Connection on I²C Bus.
DS22226A-page 29