TMP421 datasheet(11/36 Pages) TI2

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TMP421

TMP422

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SBOS398C – JULY 2007 – REVISED MAY 2012

SERIES RESISTANCE CANCELLATION

changing bit 2 (RANGE) of Configuration Register 1

from low to high. The change in measurement range

Series resistance in an application circuit that typically

and data format from standard binary to extended

results

from

printed

circuit

board

(PCB)

trace

binary occurs at the next temperature conversion. For

resistance and remote line length is automatically

data captured in the extended temperature range

cancelled by the TMP421/22/23, preventing what

configuration, an offset of 64 (40h) is added to the

would otherwise result in a temperature offset. A total

standard binary value, as shown in the Extended

of up to 3k

Ω of series line resistance is cancelled by

Binary column of Table 1. This configuration allows

the TMP421/22/23, eliminating the need for additional

measurement of temperatures as low as –64°C, and

characterization and temperature offset correction.

as high as +191°C; however, most temperature-

See the two Remote Temperature Error vs Series

sensing diodes only measure with the range of –55°C

Resistance typical characteristic curves (Figure 4 and

to +150°C. Additionally, the TMP421/22/23 are rated

Figure 5) for details on the effects of series resistance

only for ambient temperatures ranging from –40°C to

and

power-supply

voltage

sensed

remote

+125°C.

Parameters

the

Absolute

Maximum

temperature error.

Ratings table must be observed.

DIFFERENTIAL INPUT CAPACITANCE

Table 1. Temperature Data Format (Local and

Remote Temperature High Bytes)

The

TMP421/22/23

tolerate

differential

input

capacitance of up to 1000pF with minimal change in

LOCAL/REMOTE TEMPERATURE REGISTER

HIGH BYTE VALUE (1°C RESOLUTION)

temperature error. The effect of capacitance on

sensed remote temperature error is illustrated in

STANDARD BINARY(1)

EXTENDED BINARY(2)

TEMP

Figure 6, Remote Temperature Error vs Differential

(°C)

BINARY

HEX

BINARY

HEX

Capacitance.

–64

1100 0000

0000 0000

–50

1100 1110

0000 1110

TEMPERATURE MEASUREMENT DATA

–25

1110 0111

0010 0111

0000 0000

0100 0000

Temperature measurement data may be taken over

an operating range of –40°C to +127°C for both local

0000 0001

0100 0001

and remote locations.

0000 0101

0100 0101

0000 1010

0100 1010

However, measurements from –55°C to +150°C can

0001 1001

0101 1001

be made both locally and remotely by reconfiguring

0011 0010

0111 0010

the TMP421/22/23 for the extended temperature

range, as described below.

0100 1011

1000 1011

100

0110 0100

1010 0100

Temperature data that result from conversions within

125

0111 1101

1011 1101

the default measurement range are represented in

127

0111 1111

1011 1111

binary form, as shown in Table 1, Standard Binary

150

0111 1111

1101 0110

column. Note that although the device is rated to only

measure temperatures down to –55°C, it may read

175

0111 1111

1110 1111

temperatures

below

this

level.

However,

any

191

0111 1111

1111 1111

temperature below –64°C results in a data value of

(1)

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

–64 (C0h). Likewise, temperatures above +127°C

two's complement format.

result in a value of 127 (7Fh). The device can be set

(2)

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

to measure over an extended temperature range by

offset.

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