LTC2435-1IGN datasheet(35/40 Pages) LINER

35 / 40 page

LTC2435/LTC2435-1

24351fa

APPLICATIO S I FOR ATIO

Figure 42. Connecting the LTC2435/LTC2435-1 to a PIC16F73 MCU Using the SPI Serial Interface

Figure 41. Use a Differential Multiplexer to Expand Channel Capability

2435 F41

REF+

REF–

IN+

IN–

1, 7, 8, 9,

10, 15, 16

LTC2435/

LTC2435-1

VCC

GND

47µF

TO OTHER

DEVICES

74HC4052

LTC2435/

LTC2435-1

SCK

SDO

RC2

RC3

RC4

RC6

RC7

PIC16F73

2435 F42

819

VCC

T1IN

T2IN

R1OUT

R2OUT

SHDN

C1+

C1–

C2+

C2–

T1OUT

T2OUT

R1IN

R2IN

VCC

V+

V–

GND

LT1180A

Sample Driver for LTC2435/LTC2435-1 SPI Interface

Figure 41 shows the use of an LTC2435/LTC2435-1 with

a differential multiplexer. This is an inexpensive multi-

plexer that will contribute some error due to leakage if

used directly with the output from the bridge, or if

resistors are inserted as a protection mechanism from

overvoltage. Although the bridge output may be within the

input range of the A/D and multiplexer in normal opera-

tion, some thought should be given to fault conditions

that could result in full excitation voltage at the inputs to

the multiplexer or ADC. The use of amplification prior to

the multiplexer will largely eliminate errors associated

with channel leakage developing error voltages in the

source impedance.

The LTC2435/LTC2435-1 have a very simple serial inter-

face that makes interfacing to microprocessors and

microcontrollers very easy.

The listing in Figure 43 is a data collection program for the

LTC2435/LTC2435-1 using the PIC16F73 microcontroller.

The microcontroller is configured to transfer data through

the SPI serial interface. Figure 42 shows the connection.

The LT1180A is a dual RS232 driver/receiver pair with

integral charge pump that generates RS232 voltage levels

from a single 5V supply.

The program begins by declaring variables and allocating

memory locations to store the 24-bit conversion result.

The main sequence starts with pulling CS LOW. It then

waits for SDO to go LOW to start reading data. Three bytes

are read to the MCU and the LTC2435/LTC2435-1 will

automatically start a new conversion. CS is also raised to

HIGH to ensure that a new conversion is started. The

collected data are sent out through the serial port at 57600

baud. This can be captured with a terminal program and

analyzed with a spreadsheet using the HEX2DEC function.

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