MCP3421 Microchip Technology, MCP3421 Datasheet - Page 21

• Manufacturer Part Number: MCP3421
• Description: 18-Bit Analog-to-Digital Converter with I2C Interface and On-Board Reference
• Manufacturer: Microchip Technology

6.0
The MCP3421 device can be used for various precision
analog-to-digital converter applications. The device
operates with very simple connections to the
application circuit. The following sections discuss the
examples of the device connections and applications.
6.1
6.1.1
The fully differential input signals can be connected to
the V
within absolute common mode input voltage range:
V
protection diode at the input pin begins to conduct and
the error due to input leakage current increases rapidly.
Within this limit, the differential input V
is boosted by the PGA before a conversion takes place.
The MCP3421 can not accept negative input voltages
on the input pins. Figures 6-1 and 6-2 show typical con-
nection examples for differential inputs and a single-
ended input, respectively. For the single-ended input,
the input signal is applied to one of the input pins
(typically connected to the V
input pin (typically V
signal range of the single-ended configuration is from
0V to 2.048V. All device characteristics hold for the
single-ended configuration, but this configuration loses
one bit resolution because the input can only stand in
positive half scale. Refer to Section 1.0 “Electrical
Characteristics”.
6.1.2
For accurate measurement, the application circuit
needs a clean supply voltage and must block any noise
signal to the MCP3421 device.
example of using two bypass capacitors (a 10 µF
tantalum capacitor and a 0.1 µF ceramic capacitor) in
parallel on the V
filter out any high frequency noises on the V
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
possible (within one inch). If the application circuit has
separate digital and analog power supplies, the V
and V
plane.
6.1.3
The SCL and SDA pins of the MCP3421 are open-drain
configurations. These pins require a pull-up resistor as
shown in
tors depends on the operating speed (standard, fast,
and high speed) and loading capacitance of the I
© 2006 Microchip Technology Inc.
SS
- 0.3V to V
IN
SS
+ and V
BASIC APPLICATION
CONFIGURATION
Connecting to the Application
Circuits
of the MCP3421 should reside on the analog
Figure
INPUT VOLTAGE RANGE
BYPASS CAPACITORS ON V
CONNECTING TO I
PULL-UP RESISTORS
IN
DD
DD
- input pins. The input range should be
6-1. The value of these pull-up resis-
+ 0.3V. Outside this limit, the ESD
line. These capacitors are helpful to
IN
- pin) is grounded. The input
IN
+ pin) while the other
Figure 6-1
2
C BUS USING
IN
(= V
DD
IN
shows an
DD
DD
+ - V
line and
2
pin as
C bus
PIN
IN
DD
-)
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 1 kΩ and
10 kΩ ranges for standard and fast modes, and less
than 1 kΩ for high speed mode in high loading
capacitance environments.
FIGURE 6-1:
for Differential Inputs.
FIGURE 6-2:
for Single-Ended Input.
The number of devices connected to the bus is limited
only by the maximum bus capacitance of 400 pF. 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.
multiple device connections.
Input Signals
1
2
3
1
2
3
Note: R is the pull-up resistor.
Note: R is the pull-up resistor.
Input Signals
V
V
SCL
V
V
SCL
MCP3421
IN
SS
MCP3421
IN
SS
+
+
SDL
SDL
V
V
V
V
DD
DD
IN
IN
-
-
6
5
4
6
5
4
Figure 6-3
Typical Connection Example
Typical Connection Example
0.1 µF
0.1 µF
V
V
DD
DD
MCP3421
shows an example of
10 µF
10 µF
DS22003B-page 21
R
R
V
V
DD
DD
(MASTER)
(MASTER)
T
T
R
R
O
O
MCU
MCU