LTC2400IS8#PBF Datasheet LTC2400CS8#PBF, LTC2400IS8#PBF, LTC2400CS8#TRPBF | P31-P33

LTC2400

Figure 32. This BASIC Stamp Code is an Example of How Easy it is to Retrieve Data from the LTC2400

ADlo.bit0 = in0 'and sample data line

low SCK

high CS 'Disable the LTC2400

ADhi = (ADhi<<4)+((ADlo&$F000)>>12)

debug ?ADhi 'Discard the lower eight bits

goto Start 'and display (debug command).

ShiftL

Temp = ADlo.bit15 'This routine simply

ADlo = ADlo<<1 'performs a 1 bit

ADhi = ADhi<<1 'left shift on two

ADhi.bit0 = Temp '16 bit variables

return

TYPICAL APPLICATIONS

Figure 33. Connecting the LTC2400 to a 68HC11 MCU Using the SPI Serial Interface

LTC2400

SCK

SDO

SCK (PD4)

MISO (PD2)

SS (PD5)

68HC11

2400 F33

The listing in Figure 34 is a simple assembler routine for

the 68HC11 microcontroller. It uses PORT D, configuring

it for SPI data transfer between the controller and the

LTC2400. Figure 33 shows the simple 3-wire SPI

connection.

The code begins by declaring variables and allocating four

memory locations to store the 32-bit conversion result.

This is followed by initializing PORT D’s SPI configuration.

The program then enters the main sequence. It activates

the LTC2400’s serial interface by setting the SS output

low, sending a logic low to CS. It next waits in a loop for

a logic low on the data line, signifying end-of-conversion.

After the loop is satisfied, four SPI transfers are com-

pleted, retrieving the conversion. The main sequence ends

by setting SS high. This places the LTC2400’s serial

interface in a high impedance state and initiates another

conversion.

*****************************************************

* This example program transfers the LTC2400's 32-bit output *

* conversion result into four consecutive 8-bit memory locations. *

*****************************************************

*68HC11 register definition

PORTD EQU $1008 Port D data register

* " – , – , SS* ,CSK ;MOSI,MISO,TxD ,RxD"

DDRD EQU $1009 Port D data direction register

SPSR EQU $1028 SPI control register

* "SPIE,SPE ,DWOM,MSTR;SPOL,CPHA,SPR1,SPR0"

SPSR EQU $1029 SPI status register

* "SPIF,WCOL, – ,MODF; – , – , – , – "

SPDR EQU $102A SPI data register; Read-Buffer; Write-Shifter

* RAM variables to hold the LTC2400's 32 conversion result

LTC2400

TYPICAL APPLICATIONS

DIN1 EQU $00 This memory location holds the LTC2400's bits 31 - 24

DIN2 EQU $01 This memory location holds the LTC2400's bits 23 - 16

DIN3 EQU $02 This memory location holds the LTC2400's bits 15 - 08

DIN4 EQU $03 This memory location holds the LTC2400's bits 07 - 00

**********************

* Start GETDATA Routine *

**********************

ORG $C000 Program start location

INIT1 LDS #$CFFF Top of C page RAM, beginning location of stack

LDAA #$2F –,–,1,0;1,1,1,1

* –, –, SS*-Hi, SCK-Lo, MOSI-Hi, MISO-Hi, X, X

STAA PORTD Keeps SS* a logic high when DDRD, bit 5 is set

LDAA #$38 –,–,1,1;1,0,0,0

STAA DDRD SS*, SCK, MOSI are configured as Outputs

* MISO, TxD, RxD are configured as Inputs

*DDRD's bit 5 is a 1 so that port D's SS* pin is a general output

LDAA #$50

STAA SPCR The SPI is configured as Master, CPHA = 0, CPOL = 0

* and the clock rate is E/2

* (This assumes an E-Clock frequency of 4MHz. For higher E-

* Clock frequencies, change the above value of $50 to a value

* that ensures the SCK frequency is 2MHz or less.)

GETDATA PSHX

PSHY

PSHA

LDX #$0 The X register is used as a pointer to the memory locations

* that hold the conversion data

LDY #$1000

BCLR PORTD, Y %00100000 This sets the SS* output bit to a logic

* low, selecting the LTC2400

TRFLP1 LDAA #$0 Load accumulator A with a null byte for SPI transfer

STAA SPDR This writes the byte in the SPI data register and starts

* the transfer

WAIT1 LDAA SPSR This loop waits for the SPI to complete a serial

transfer/exchange by reading the SPI Status Register

BPL WAIT1 The SPIF (SPI transfer complete flag) bit is the SPSR's MSB

* and is set to one at the end of an SPI transfer. The branch

* will occur while SPIF is a zero.

LDAA SPDR Load accumulator A with the current byte of LTC2400 data

that was just received

STAA 0,X Transfer the LTC2400's data to memory

INX Increment the pointer

CPX #DIN4+1 Has the last byte been transferred/exchanged?

BNE TRFLP1 If the last byte has not been reached, then proceed to the

* next byte for transfer/exchange

BSET PORTD,Y %00100000 This sets the SS* output bit to a logic high,

* de-selecting the LTC2400

PULA Restore the A register

PULY Restore the Y register

PULX Restore the X register

RTS

Figure 34. This is an Example of 68HC11 Code That Captures the LTC2400’s

Conversion Results Over the SPI Serial Interface Shown in Figure 33

LTC2400

Thermocouple Applications

Figure 35 shows a thermocouple interface circuit that

demonstrates the practicality of direct connection to the

LTC2400 using even the lowest output thermocouples (in

this case, a type S thermocouple, with a full-scale output

of 18mV).

This topology is the least costly solution for thermocouple

sensing. As shown, it is capable of resolving approxi-

mately 0.25°C without averaging. Since the LTC2400 does

not exhibit any easily discernible quantization effects,

averaging can significantly extend the resolution for slow

changing processes.

In this circuit, a 1N4148 diode provides cold junction

compensation by producing, at the positive terminal of the

thermocouple, an approximation of the average Seebeck

coefficient for a type S thermocouple over the temperature

range expected at the cold junction (0°C to 40°C). If the

operating range is less, the coefficient can be adjusted to

produce a better match for the range anticipated. This

basic circuit can be used with other thermocouples by

changing the divide ratio to suit the Seebeck coefficient of

the type chosen (see table).

TYPICAL APPLICATIONS

This circuit produces a DC offset at the cold junction

reference point, of 1mV to 15mV, which must be nulled out

in software. This DC offset, resulting from the forward

voltage of the diode, is variable from device to device and

must be calibrated for each unit.

Since the temperature coefficient of the 1N4148 diode is

not guaranteed, a trim should be provided to accommo-

date a coefficient from 1.7mV/°C to 2.3mV/°C. Alterna-

tively, a transistor can be used as a sensor with Omega

Engineering thermocouple circuit board connectors that

are available with TO-92 transistor retainer clips, placing

the transistor in physical contact with the cold junction.

The 1M resistor R

shown is intended as an open-circuit

detection scheme, producing full scale at the input of the

LTC2400. Note that this resistor contributes to the offset

and must have low TC, as should the resistors R2 and R3.

Since R1 provides forward bias for the diode, its tempera-

ture coefficient is not as critical.

The circuit in Figure 35 uses only 12% of the LTC2400’s

input range and is able to accommodate the full-scale

output of all thermocouple types. The commonly used

SDO

SCK

THERMOCOUPLE

43.2k

10k

REF

0.1µF

GND

LTC2400

2400 F35

–

1N4148

COLD JUNCTION

ISOTHERMAL

R2*

–2mV/°C

60Hz

*25ppm, 1% TOLERANCE

SINGLE POINT GROUND

50Hz

–SB

R3*

100Ω

*20°C ≤ T

≤ 50°C

THERMOCOUPLE

TYPE

SEEBECK

COEFFICIENT*

50.2µV/°C

39.2µV/°C

6.15µV/°C

3.83k

4.99k

32.4k

Figure 35. Diode Cold Junction Compensation

P1-P3 P4-P6 P7-P9 P10-P12 P13-P15 P16-P18 P19-P21 P22-P24 P25-P27 P28-P30 P31-P33 P34-P36 P37-P39 P40-P40

LTC2400IS8#PBF

Mfr. #:

Buy LTC2400IS8#PBF

Manufacturer:

Analog Devices Inc.

Description:

Analog to Digital Converters - ADC 24-B Pwr No Lat Delta-Sigma ADC in SO-

Lifecycle:

New from this manufacturer.

Delivery:

DHL FedEx Ups TNT EMS

Payment:

T/T Paypal Visa MoneyGram Western Union

LTC2400IS8#PBF

LTC2400IS8#PBF

Products related to this Datasheet