Microchip Technology MCP3422EV Data Sheet

© 2009 Microchip Technology Inc.

DS22088C-page 31

The MCP3422/3/4 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.

6.1.1

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 MCP3422/3/4 devices. 

 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 MCP3424. 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 MCP3422/3/4 devices 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 MCP3422/3/4 are open-
drain configurations. These pins require a pull-up
resistor as shown in 

. The value of these

pull-up resistors depends on the operating speed
(standard, fast, and high speed) and loading
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

Ω and 10 kΩ ranges for standard and fast

modes, and less than 1 k

Ω for high speed mode

depending on the presence of bus loading capacitance.

6.1.3

I

2

C ADDRESS SELECTION PINS 

(

MCP3423

 AND 

MCP3424

)

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 (MCP3423 and MCP3424)”.

 

 shows an example of multiple device

connections. The I

2

C bus loading capacitance

increases as the number of device connected to the I

2

C

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 I

2

C

devices that are connected to the I

2

C bus line.

 

R

P

V

DD

4

5

6

9

CH2-

 V

SS

CH3+

Adr1

Adr0

3

12

CH2+

CH3-

2

13

CH1-

CH4+

1

14

CH1+

CH4-

7

8

 SDA

SCL

 V

DD

11

10

C

1

C

2

Input 

Input 
Signal 2

Signal 1

Input 

Input 

Signal 4

Signal 3

T

O

 MCU

(MASTER)

R

P

I

2

C Address

Selection 
Pins

Rp is the pull-up resistor:

5 k

Ω - 10 kΩ for f

SCL

=

100 kHz to 400 kHz

~700

Ω for f

SCL

=

3.45 MHz

C1: 0.1 µF, Ceramic capacitor

C2: 10 µF, Tantalum capacitor

SDA SCL

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