Microchip Technology TMPSNSRD-TCPL1 データシート
© 2009 Microchip Technology Inc.
DS22003E-page 27
MCP3421
6.0
BASIC APPLICATION
CONFIGURATION
CONFIGURATION
The MCP3421 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.
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
Connecting to the Application
Circuits
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 MCP3421 device.
needs a clean supply voltage and must block any noise
signal to the MCP3421 device.
shows an
example of using two bypass capacitors (a 10 µF
tantalum capacitor and a 0.1 µF ceramic capacitor) on
the V
tantalum capacitor and a 0.1 µF ceramic capacitor) on
the V
DD
line of the MCP3421. These capacitors are
helpful to filter out any high frequency noises on the
V
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
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
circuit has separate digital and analog power supplies,
the V
DD
and V
SS
of the MCP3421 device should reside
on the analog plane.
6.1.2
CONNECTING TO I
2
C BUS USING
PULL-UP RESISTORS
The SCL and SDA pins of the MCP3421 are open-drain
configurations. These pins require a pull-up resistor as
shown in
configurations. These pins require a pull-up resistor as
shown in
. The value of these pull-up
resistors depends on the operating speed and loading
capacitance of the I
capacitance of the I
2
C 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 k
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 k
Ω and 10 kΩ ranges for standard and fast
modes.
FIGURE 6-1:
Typical Connection
Example.
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.
only by the maximum bus capacitance of 400 pF. The
bus loading capacitance affects on the bus operating
speed.
shows an example of multiple device
connections.
FIGURE 6-2:
Example of Multiple Device
Connection on I
2
C Bus.
V
IN
+
V
IN
-
V
DD
V
SS
1
2
3
3
4
5
6
SCL
SDL
R
p
Input Signals
V
DD
V
DD
T
O
MCU
(MASTER)
R
P
is the pull-up resistor:
5 k
Ω - 10 kΩ for f
SCL
= 100 kHz to 400 kHz
C1: 0.1 µF, Ceramic capacitor
C2: 10 µF, Tantalum capacitor
R
p
C1
C2
MCP3421
SDA
SCL
Microcontroller
Temperature
(PIC16F876)
MCP4725
Sensor
(
MCP9804)
MCP3421