LTC2995 datasheet(67/90 Pages) AD

67 / 90 page

LTM2985

Rev. 0

For more information www.analog.com

APPLICATIONS INFORMATION

Figure 52 shows the interface to a thermocouple us-

ing the LTM2985 multi-sensor circuit. In this case, the

thermocouple ties directly to terminals T3 and T4 while

terminals T1 and T2 can be left floating or tied to an RTD

(Global Register G5 = 1) or thermistor (Global Register G6

= 1) for cold junction compensation. Alternatively, a diode

(tied to CH9) can be used for cold junction compensation.

The thermocouple is assigned to CH6 with single ended

measurement mode.

Figure 52. Protected Multi-Sensor Thermocouple Connection

RP6

2985 F52

CH3

CH2

CH1

CH4

CH5

CH8

CH9

COM

CH7

CH6

RP2

RP3

RP8

RP5

RSENSE

RP4

RP1

RP7

OPTIONAL

RTD FOR CJ

G5 = 1

OPTIONAL

THERMISTOR

FOR CJ

G6 = 1

THERMOCOUPLE

OPTIONAL

DIODE

FOR CJ

ACTIVE ANALOG TEMPERATURE SENSORS

In addition to passive type temperature sensors, the

LTM2985alsosupportsactiveanalogtemperaturesensors

(e.g., LTC2997). In this mode, the LTM2985 measures

the voltage output from the analog temperature sensor

and does a table lookup to convert the measured voltage

to temperature. This sensor option is fully customizable

and can be used for direct temperature measurement or

cold junction compensation.

Analog Sensor Channel Assignment and Result Formats

For the active analog temperature sensor type = 31 (see

Table 4 and Figure 53), the channel assignment word is

0xF800 0000 for differential measurements and 0xFC00

0000 for single-ended. When the LTM2985 is configured

for the active analog temperature sensor type, it will take

the measured voltage value from the ADC and perform a

table lookup to produce a temperature result. The result

format of the table lookup will be a 24-bit signed fixed-

point temperature result along with the error status byte.

The fixed-point format of the temperature is identical to

all the other LTM2985 temperature sensor types. This

format can be seen in Table 9A and Table 9B.

Figure 53. Active Analog Temperature Sensor Channel Assignment Conventions

2985 F53

CHADC

SINGLE-ENDED

CHANNEL

ASSIGNMENT

= CHADC (1 ≤ CHADC ≤ 10)

= CHADC (2 ≤ CHADC ≤ 10)

24-BIT

∆∑ ADC

24-BIT

∆∑ ADC

CHANNEL

ASSIGNMENT

DIFFERENTIAL

COM

CHADC

CHADC-1

–

LOOKUP

TABLE

WITH

INTERPOLATION

TEMPERATURE

OUTPUT

LOOKUP

TABLE

WITH

INTERPOLATION

TEMPERATURE

OUTPUT

ACTIVE ANALOG

TEMPERATURE

SENSOR

VCC2

ACTIVE ANALOG

TEMPERATURE

SENSOR

VCC2

LTC2995 Datasheet(PDF) 67 Page - Analog Devices

LTC2995 Datasheet(HTML) 67 Page - Analog Devices

Html Pages

1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 58 59 60 61 62 63 64 65 66 67 68 69 70 71 72 73 74 75 76 77 78 79 80 81 82 83 84 85 86 87 88 89 90

Datasheet Download

Link URL