MCP3421 datasheet(27/42 Pages) MICROCHIP

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DS22003E-page 27

MCP3421

6.0

BASIC APPLICATION

CONFIGURATION

The MCP3421 can be used for various precision

analog-to-digital converter applications. The device

operates

with

very

simple

connections

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 VDD PIN

For an accurate measurement, the application circuit

needs a clean supply voltage and must block any noise

signal to the MCP3421 device. 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 VDD line of the MCP3421. These capacitors are

helpful to filter out any high frequency noises on the

VDD 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 VDD

pin as possible (within one inch). If the application

circuit has separate digital and analog power supplies,

the VDD and VSS of the MCP3421 device should reside

on the analog plane.

6.1.2

CONNECTING TO I2C 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 Figure 6-1. The value of these pull-up

resistors depends on the operating 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 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. Figure 6-2 shows an example of multiple device

connections.

FIGURE 6-2:

Example of Multiple Device

Connection on I2C Bus.

VIN+

VIN-

VDD

VSS

SCL

SDL

Input Signals

VDD

TO MCU

(MASTER)

RP is the pull-up resistor:

Ω - 10 kΩ for f

SCL

= 100 kHz to 400 kHz

C1: 0.1 µF, Ceramic capacitor

C2: 10 µF, Tantalum capacitor

MCP3421

SDA

SCL

Microcontroller

Temperature

(PIC16F876)

MCP4725

Sensor

(

MCP9804)

MCP3421

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