TMP422-EP

www.ti.com

SBOS577

– SEPTEMBER 2011

SERIES RESISTANCE CANCELLATION

Series resistance in an application circuit that typically results from printed circuit board (PCB) trace resistance

and remote line length is automatically cancelled by the TMP422, preventing what would otherwise result in a

temperature offset. A total of up to 3k

Ω of series line resistance is cancelled by the TMP422, eliminating the

need for additional characterization and temperature offset correction. See the two Remote Temperature Error vs

Series Resistance typical characteristic curves (Figure 4 and Figure 5) for details on the effects of series

resistance and power-supply voltage on sensed remote temperature error.

DIFFERENTIAL INPUT CAPACITANCE

The TMP422 tolerates differential input capacitance of up to 1000pF with minimal change in temperature error.

The effect of capacitance on sensed remote temperature error is illustrated in Figure 6, Remote Temperature

Error vs Differential Capacitance.

TEMPERATURE MEASUREMENT DATA

Temperature measurement data may be taken over an operating range of

–40°C to +127°C for both local and

remote locations.

However, measurements from

–55°C to +150°C can be made both locally and remotely by reconfiguring the

TMP422 for the extended temperature range, as described below.

Temperature data that result from conversions within the default measurement range are represented in binary

form, as shown in Table 2, Standard Binary column. Note that although the device is rated to only measure

temperatures down to

–55°C, it may read temperatures below this level. However, any temperature below –64°C

results in a data value of

–64 (C0h). 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 1 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 2. 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 TMP422 is rated only for ambient temperatures ranging from

–55°C to +125°C. Parameters in

the Absolute Maximum Ratings table must be observed.

Table 2. Temperature Data Format (Local and Remote Temperature High Bytes)

LOCAL/REMOTE TEMPERATURE REGISTER

HIGH BYTE VALUE (1

°C RESOLUTION)

TEMP

(

°C)

BINARY

HEX

BINARY

HEX

–64

1100 0000

C0

0000 0000

00

–50

1100 1110

CE

0000 1110

0E

–25

1110 0111

E7

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 two's complement format.

(2)

Resolution is 1

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

Copyright

© 2011, Texas Instruments Incorporated

Submit Documentation Feedback

9

Product Folder Link(s): TMP422-EP