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LTC2486

2486f

Temperature Sensor

The LTC2486 includes an integrated temperature sensor.

The temperature sensor is selected by setting IM = 1. The

digital output is proportional to the absolute temperature

of the device. This feature allows the converter to perform

cold junction compensation for external thermocouples or

continuously remove the temperature effects of external

sensors.

The internal temperature sensor output is 28mV at 27°C

(300°K), with a slope of 93.5µV/°C independent of VREF

(see Figures 4 and 5). Slope calibration is not required if

the reference voltage (VREF) is known. A 5V reference has

a slope of 2.45 LSBs16/°C. The temperature is calculated

from the output code (where DATAOUT16 is the decimal

representation of the 16-bit result) for a 5V reference using

the following formula:

TK = DATAOUT16 /2.45 in Kelvin

If a different value of VREF is used, the temperature output

is:

TK = DATAOUT16 /(0.49 • VREF) in Kelvin

If the value of VREF is not known, the slope is determined by

measuring the temperature sensor at a known temperature

TN (in °K) and using the following formula:

SLOPE = DATAOUT16/TN

APPLICATIONS INFORMATION

Table 5a. Performance vs Gain in Normal Speed Mode (VCC = 5V, VREF = 5V)

GAIN

128

256

UNIT

Input Span

±2.5

±0.625

±0.312

±0.156

±78m

±39m

±19.5m

±9.76m

LSB

38.1

9.54

4.77

2.38

1.19

0.596

0.298

0.149

µV

Noise Free Resolution*

65536

32768

16384

Counts

Gain Error

ppm of FS

Offset Error

0.5

µV

Table 5b. Performance vs Gain in 2x Speed Mode (VCC = 5V, VREF = 5V)

GAIN

128

UNIT

Input Span

±2.5

±1.25

±0.625

±0.312

±0.156

±78m

±39m

±19.5m

LSB

38.1

19.1

9.54

4.77

2.38

1.19

0.596

0.298

µV

Noise Free Resolution*

65536

45875

22937

Counts

Gain Error

ppm of FS

Offset Error

200

µV

*The resolution in counts is calculated as the FS divided by LSB or the RMS noise value, whichever is larger.

This value of slope can be used to calculate further tem-

perature readings using:

TK = DATAOUT16 /SLOPE

All Kelvin temperature readings can be converted to TC

(°C) using the fundamental equation:

TC = TK – 273

SERIAL INTERFACE TIMING MODES

The LTC2486’s 4-wire interface is SPI and MICROWIRE

compatible. This interface offers several ﬂexible modes

of operation. These include internal/external serial clock,

3- or 4-wire I/O, single cycle or continuous conversion. The

following sections describe each of these timing modes

in detail. In all cases, the converter can use the internal

oscillator (FO = LOW) or an external oscillator connected

to the FO pin. For each mode, the operating cycle, data

input format, data output format, and performance remain

the same. Refer to Table 6 for a summary.

External Serial Clock, Single Cycle Operation

This timing mode uses an external serial clock to shift out

the conversion result and

⎯C⎯S to monitor and control the

state of the conversion cycle (see Figure 6).

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