TMP451

SBOS686 – JUNE 2013

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SERIES RESISTANCE CANCELLATION

Series resistance cancellation automatically eliminates the temperature error caused by the resistance of the

routing to the remote transistor or by the resistors of the optional external low-pass filter. A total of up to 1 k

Ω of

series resistance can be cancelled by the TMP451, eliminating the need for additional characterization and

temperature offset correction. See Figure 4, Remote Temperature Error vs Series Resistance, for details on the

effects of series resistance on sensed remote temperature error.

DIFFERENTIAL INPUT CAPACITANCE

The TMP451 tolerates differential input capacitance of up to 1000 pF with minimal change in temperature error.

The effect of capacitance on sensed remote temperature error is illustrated in Figure 5, Remote Temperature

Error vs Differential Capacitance.

TEMPERATURE MEASUREMENT DATA

The local and remote temperature sensors have a resolution of 12 bits (0.0625°C). Temperature data that result

from conversions within the default measurement range are represented in binary form, as shown in the

Standard Binary column of Table 1. Any temperature below 0°C results in a data value of 0 (00h). Likewise,

temperatures above +127°C result in a value of 127 (7Fh). The device can be set to measure over an extended

temperature range by changing bit 2 (RANGE) of configuration register from low to high. The change in

measurement range and data format from standard binary to extended binary occurs at the next temperature

conversion. For data captured in the extended temperature range configuration, an offset of 64 (40h) is added to

the standard binary value, as shown in the Extended Binary column of Table 1. This configuration allows

measurement of temperatures as low as –64°C, and as high as +191°C; however, most temperature-sensing

diodes only measure with the range of –55°C to +150°C. Additionally, the TMP451 is specified only for ambient

temperatures ranging from –40°C to +125°C; parameters in the Absolute Maximum Ratings table must be

observed.

Table 1. Temperature Data Format (Local and Remote Temperature High Bytes)

LOCAL/REMOTE TEMPERATURE REGISTER

HIGH BYTE VALUE (1°C RESOLUTION)

TEMPERATURE

(°C)

BINARY

HEX

BINARY

HEX

–64

0000 0000

00

0000 0000

00

–50

0000 0000

00

0000 1110

0E

–25

0000 0000

00

0010 0111

27

0

0000 0000

00

0100 0000

40

1

0000 0001

01

0100 0001

41

5

0000 0101

05

0100 0101

45

10

0000 1010

0A

0100 1010

4A

25

0001 1001

19

0101 1001

59

50

0011 0010

32

0111 0010

72

75

0100 1011

4B

1000 1011

8B

100

0110 0100

64

1010 0100

A4

125

0111 1101

7D

1011 1101

BD

127

0111 1111

7F

1011 1111

BF

150

0111 1111

7F

1101 0110

D6

175

0111 1111

7F

1110 1111

EF

191

0111 1111

7F

1111 1111

FF

(1)

Resolution is 1°C/count. Negative numbers are represented in twos complement format.

(2)

Resolution is 1°C/count. All values are unsigned with a –64°C offset.

8

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