Datasheet

ADS1118

SBAS457D –OCTOBER 2010–REVISED OCTOBER 2013

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TEMPERATURE SENSOR

The temperature measurement mode of the ADS1118 is configured as a 14-bit result when enabled. Two bytes

must be read to obtain data. The first byte is the most significant byte (MSB), followed by a second byte, the

least significant byte (LSB). The first 14 bits are used to indicate temperature. That is, the 14-bit temperature

result is left-justified within the 16-bit result register and the last two bits always read back as '0'. One 14-bit LSB

equals 0.03125°C. Negative numbers are represented in binary twos complement format.

Table 4. 14-bit Temperature Data Format

TEMPERATURE (°C) DIGITAL OUTPUT (BINARY) HEX

128 01 0000 0000 0000 1000

127.96875 00 1111 1111 1111 0FFF

100 00 1100 1000 0000 0C80

80 00 1010 0000 0000 0A00

75 00 1001 0110 0000 0960

50 00 0110 0100 0000 0640

25 00 0011 0010 0000 0320

0.25 00 0000 0000 1000 0008

0 00 0000 0000 0000 0000

–0.25 11 1111 1111 1000 3FF8

–25 11 1100 1110 0000 3CE0

–55 11 1001 0010 0000 3920

Converting from Temperature to Digital Codes

For positive temperatures (for example, +50°C):

Twos complement is not performed on positive numbers. Therefore, simply convert the number to binary

code in a 14-bit left justified format with the MSB = 0 to denote the positive sign.

Example: (+50°C)/(0.03125°C/count) = 1600 = 0640h = 00 0110 0100 0000

For negative temperatures (for example –25°C):

Generate the twos complement of a negative number by complementing the absolute binary number and

adding 1. Then denote the negative sign with the MSB = 1.

Example:(|–25°C|)/(0.03125°C/count) = 800 = 0320h = 00 0011 0010 0000

Twos complement format: 11 1100 1101 1111 + 1 = 11 1100 1110 0000

Converting from Digital Codes to Temperature

To convert from digital codes to temperature, first check whether the MSB is a '0' or a '1'. If the MSB is a '0',

simply multiply the decimal code by 0.03125°C to obtain the result. If the MSB = 1, subtract '1' from the result

and complement all of the bits. Then multiply the result by –0.03125°C.

Example: ADS1118 reads back 0960h: 0960h has an MSB = 0.

(0960h) × (0.03125°C) = (2400) × (0.03125°C) = +75°C

Example: ADS1118 reads back 3CE0h: 3CE0h has an MSB = 1.

Complement the result: 3CE0h → 0320h

(0320h) × (–0.03125°C) = (800) × (–0.03125°C) = –25°C

Product Folder Links: ADS1118