LTC2414IGN datasheet(42/48 Pages) LINER

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LTC2414/LTC2418

241418fa

APPLICATIO S I FOR ATIO

•

SDI

SCK

SDO

REF+

REF–

CH0

CH1

CH2

CH3

CH14

CH15

•

GND

VCC

LTC2418

0.1

µF

25k

0.1%

PT2

100

Ω

RTD

PT1

100

Ω

RTD

PT8

100

Ω

RTD

2418 F48

µF

4-WIRE

SPI

Figure 48. Measurement of a Ladder of Sensors Using

Differential Mode

Multichannel Bridge Digitizer and Digital Cold

Junction Compensation

The bridge application as shown in Figures 41, 42, and 43

can be expanded to multiple bridge transducers. Figure 54

shows the expansion for simple bridge measurement.

Also included is the temperature measurement.

In Figure 54, CH0 to CH13 are configured as differential to

measure up to seven bridge transducers using the LTC2418.

CH14 and CH15 are configured as single-ended. CH14

measures the thermocouple while CH15 measures the

output of the cold junction sensor (diode, thermistor,

etc.). The measured cold junction sensor output is then

used to compensate the thermocouple output to find the

absolute temperature. The final temperature value may

then be used to compensate the temperature effects of the

bridge transducers.

Sample Driver for LTC2414/LTC2418 SPI Interface

The LTC2414/LTC2418 have a simple 4-wire serial inter-

face and it is easy to program microprocessors and

microcontrollers to control the device.

Figure 49 shows the 4-wire SPI connection between the

LTC2414/LTC2418 and a PIC16F84 microcontroller. The

sample program for CC5X compiler in Figure 50 can be

used to program the PIC16F84 to control the LTC2414/

LTC2418. It uses PORT B to interface with the device.

The program begins by declaring variables and allocating

four memory locations to store the 32-bit conversion

result. In execution, it first initiates the PORT B to the

proper SPI configuration and prepares channel address.

The LTC2414/LTC2418 is activated by setting the CS low.

Then the microcontroller waits until a logic LOW is de-

tected on the data line, signifying end-of-conversion. After

a LOW is detected, a subroutine is called to exchange data

between the LTC2414/LTC2418 and the microcontroller.

The main loop ends by setting CS high, ending the data

output state.

The performance of the LTC2414/LTC2418 can be verified

using the demonstration board DC434A, see Figure 51 for

the schematic. This circuit uses the computer’s serial port

to generate power and the SPI digital signals necessary for

starting a conversion and reading the result. It includes a

SCK

SDI

SDO

PIC16F84

LTC2414/

LTC2418

RB2

RB3

RB4

RB5

2414/18 F49

Figure 49. Connecting the LTC2414/LTC2418 to

a PIC16F84 MCU Using the SPI Serial Interface

LabVIEW

TM application software program (see Figure 52)

which graphically captures the conversion results. It can

be used to determine noise performance, stability and with

an external source linearity. As exemplified in the sche-

matic, the LTC2414/LTC2418 is extremely easy to use.

This demonstration board and associated software is

available by contacting Linear Technology.

LTC2414IGN 데이터시트(PDF) 42 Page - Linear Technology

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