Datasheet
BETA COMPENSATION TEMPERATURE MEASUREMENT DATA
SERIES RESISTANCE CANCELLATION
DIFFERENTIAL INPUT CAPACITANCE
TMP441
TMP442
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.............................................................................................................................................. SBOS425A – DECEMBER 2008 – REVISED MARCH 2009
Previous generations of remote junction temperature Temperature measurement data are taken over a
sensors were operated by controlling the emitter default range of – 55 ° C to +127 ° C for both local and
current of the sensing transistor. However, remote locations. However, measurements from
examination of the physics of a transistor shows that – 55 ° C to +150 ° C can be made both locally and
V
BE
is actually a function of the collector current. If remotely by reconfiguring the TMP441/42 for the
beta is independent of the collector current, then V
BE
extended temperature range, as described in this
may be calculated from the emitter current. In earlier section. Temperature data resulting from conversions
generations of processors that contained PNP within the default measurement range are
transistors connected to these temperature sensors, represented in binary form, as shown in Table 1 ,
controlling the emitter current provided acceptable Standard Binary column. Note that any temperature
temperature measurement results. At 90nm process below – 64 ° C results in a data value of – 64 (C0h).
geometry and below, the beta factor continues to Likewise, temperatures above +127 ° C result in a
decrease and the premise that it is independent of value of 127 (7Fh). The device can be set to measure
collector current becomes less certain. over an extended temperature range by changing bit
2 (RANGE) of Configuration Register 1 from low to
To manage this increasing temperature measurement
high. The change in measurement range and data
error, the TMP441/42 control the collector current
format from standard binary to extended binary
instead of the emitter current. The TMP441/42
occurs at the next temperature conversion. For data
automatically detect and choose the correct range
captured in the extended temperature range
depending on the beta factor of the external
configuration, an offset of 64 (40h) is added to the
transistor. This auto-ranging is performed at the
standard binary value, as shown in the Extended
beginning of each temperature conversion in order to
Binary column of Table 1 . This configuration allows
correct for any changes in the beta factor as a result
measurement of temperatures as low as – 64 ° C, and
of temperature variation. The device can operate a
as high as +191 ° C; however, most
PNP transistor with a beta factor as low as 0.1. See
temperature-sensing diodes only measure with the
the Beta Compensation Configuration Register
range of – 55 ° C to +150 ° C. Additionally, the
Section for further information.
TMP441/42 are rated only for ambient temperatures
ranging from – 40 ° C to +125 ° C. Parameters in the
Absolute Maximum Ratings table must be observed.
Series resistance in an application circuit that typically
Table 1. Temperature Data Format (Local and
results from printed circuit board (PCB) trace
Remote Temperature High Bytes)
resistance and remote line length (see Figure 12 ) is
automatically cancelled by the TMP441/42,
LOCAL/REMOTE TEMPERATURE REGISTER
HIGH BYTE VALUE (1 ° C RESOLUTION)
preventing what would otherwise result in a
STANDARD BINARY
(1)
EXTENDED BINARY
(2)
temperature offset. A total of up to 1k Ω of series line
TEMP
resistance is cancelled by the TMP441/42 if beta ( ° C) BINARY HEX BINARY HEX
correction is disabled and up to 300 Ω of series line
– 64 1100 0000 C0 0000 0000 00
resistance is cancelled if beta correction is enabled,
– 50 1100 1110 CE 0000 1110 0E
eliminating the need for additional characterization
– 25 1110 0111 E7 0010 0111 27
and temperature offset correction. See the two
0 0000 0000 00 0100 0000 40
Remote Temperature Error vs Series Resistance
1 0000 0001 01 0100 0001 41
typical characteristic curves (Figure 7 and Figure 8 )
5 0000 0101 05 0100 0101 45
for details on the effect of series resistance on
10 0000 1010 0A 0100 1010 4A
sensed remote temperature error.
25 0001 1001 19 0101 1001 59
50 0011 0010 32 0111 0010 72
75 0100 1011 4B 1000 1011 8B
The TMP441/42 can tolerate differential input
100 0110 0100 64 1010 0100 A4
capacitance of up to 500pF if beta correction is
125 0111 1101 7D 1011 1101 BD
enabled, and 1000pF if beta correction is disabled
127 0111 1111 7F 1011 1111 BF
with minimal change in temperature error. The effect
150 0111 1111 7F 1101 0110 D6
of capacitance on sensed remote temperature error is
illustrated in Figure 9 , Remote Temperature Error vs 175 0111 1111 7F 1110 1111 EF
Differential Capacitance. See the Filtering section for
191 0111 1111 7F 1111 1111 FF
suggested component values where filtering
(1) Resolution is 1 ° C/count. Negative numbers are represented in
unwanted coupled signals is needed.
twos complement format.
(2) Resolution is 1 ° C/count. All values are unsigned with a – 64 ° C
offset.
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