MCP47DA1 datasheet(57/76 Pages) MICROCHIP

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 2012-2013 Microchip Technology Inc.

DS25118D-page 57

MCP47DA1

8.6.2

PCB AREA REQUIREMENTS

In some applications, PCB area is a criteria for device

selection. Table 8-2 shows the typical package

dimensions and area for the different package options.

TABLE 8-2:

PACKAGE FOOTPRINT (1)

8.6.3

FOOTPRINT COMPATIBILITY WITH

MCP40D18

The MCP47DA1 in the SC70 package is footprint com-

patible with the MCP40D18 device. The VREF pin is

analogous to the A Terminal pin while the VOUT pin is

analogous to the W Terminal pin. The VOUT pin is a

buffered output so any buffering of the W Terminal pin

may be able to be removed. Also, verify the resistor

network’s resistance to ensure the voltage source on

the VREF pin (A Terminal) can support the current

requirements (IVREF vs. the IRAB).

8.6.4

CONNECTING TO I2C BUS USING

PULL-UP RESISTORS

The SCL and SDA pins of the MCP47DA1 devices are

open-drain configurations. These pins require a pull-up

resistor as shown in Figure 8-9.

The pull-up resistor values (R1 and R2) for SCL and

SDA pins depend on the operating speed (standard,

fast, and high speed) and loading capacitance of the

I2C bus line. A higher value of the pull-up resistor

consumes less power, but increases the signal

transition time (higher RC time constant) on the bus

line. Therefore, it can limit the bus operating speed.

The lower resistor value, on the other hand, consumes

higher power, but allows higher operating speed. If the

bus line has higher capacitance due to long metal

traces or multiple device connections to the bus line, a

smaller pull-up resistor is needed to compensate the

long RC time constant. The pull-up resistor is typically

chosen between 1 k

and 10 kranges for Standard

and Fast modes.

8.6.4.1

Device Connection Test

The user can test the presence of the device on the I2C

bus line using a simple I2C command. This test can be

achieved by checking an acknowledge response from

the device after sending a Read or Write command.

Figure 8-10 shows an example with a Read command.

The steps are:

a) Set the R/W bit “High” in the device’s address

byte.

b) Check the ACK bit of the address byte.

If the device acknowledges (ACK = 0) the

command, then the device is connected,

otherwise it is not connected.

Send Stop bit.

FIGURE 8-10:

I2C Bus Connection Test.

Package

Package Footprint

Type

Code

Dimensions (mm)

Length

Width

SOT-23

3.10

3.20

9.92

SC70

2.0

2.10

4.20

Note 1: Does not include recommended Land

Pattern dimensions. Dimensions are

max. values.

12 3

5 6

SCL

SDA

11 0

1A2 A1 A0 1

Start

Bit

Address Byte

Address bits

Device Code

R/W

Stop

Bit

Device

Response

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