Datasheet

TMP421
TMP422
TMP423
www.ti.com 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 3kΩ 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 on sensed remote
+125°C. Parameters in 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 C0 0000 0000 00
–50 1100 1110 CE 0000 1110 0E
TEMPERATURE MEASUREMENT DATA
–25 1110 0111 E7 0010 0111 27
0 0000 0000 00 0100 0000 40
Temperature measurement data may be taken over
an operating range of –40°C to +127°C for both local
1 0000 0001 01 0100 0001 41
and remote locations.
5 0000 0101 05 0100 0101 45
10 0000 1010 0A 0100 1010 4A
However, measurements from –55°C to +150°C can
25 0001 1001 19 0101 1001 59
be made both locally and remotely by reconfiguring
50 0011 0010 32 0111 0010 72
the TMP421/22/23 for the extended temperature
range, as described below.
75 0100 1011 4B 1000 1011 8B
100 0110 0100 64 1010 0100 A4
Temperature data that result from conversions within
125 0111 1101 7D 1011 1101 BD
the default measurement range are represented in
127 0111 1111 7F 1011 1111 BF
binary form, as shown in Table 1, Standard Binary
150 0111 1111 7F 1101 0110 D6
column. Note that although the device is rated to only
measure temperatures down to –55°C, it may read
175 0111 1111 7F 1110 1111 EF
temperatures below this level. However, any
191 0111 1111 7F 1111 1111 FF
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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