Datasheet

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SBOS383C − DECEMBER 2006 − REVISED MAY 2008
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7
SERIES RESISTANCE CANCELLATION
Series resistance in an application circuit that typically
results from printed circuit board (PCB) trace resistance
and remote line length (see Figure 11) is automatically
cancelled by the TMP411, preventing what would
otherwise result in a temperature offset.
A total of up to 3kΩ of series line resistance is cancelled
by the TMP411, eliminating the need for additional
characterization and temperature offset correction.
See the two Remote Temperature Error vs Series
Resistance typical characteristics curves for details on the
effect of series resistance and power-supply voltage on
sensed remote temperature error.
DIFFERENTIAL INPUT CAPACITANCE
The TMP411 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 typical characteristic Remote Temperature
Error vs Differential Capacitance. (Figure 6).
TEMPERATURE MEASUREMENT DATA
Temperature measurement data are taken over a default
range of 0°C to +127°C for both local and remote locations.
Measurements from −55°C to +150°C can be made both
locally and remotely by reconfiguring the TMP411 for the
extended temperature range. To change the TMP411
configuration from the standard to the extended
temperature range, switch bit 2 (RANGE) of the
Configuration Register from low to high.
Temperature data resulting from conversions within the
default measurement range are represented in binary
form, as shown in Table 1, Standard Binary column. Note
that any temperature below 0°C results in a data value of
zero (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 of
the 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 Table 1,
Extended Binary column. This configuration allows
measurement of temperatures below 0°C. Note that binary
values corresponding to temperatures as low as −64°C,
and as high as +191°C are possible; however, most
temperature sensing diodes only measure with the range
of −55°C to +150°C. Additionally, the TMP411 is rated only
for ambient local 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)
TEMP
STANDARD BINARY EXTENDED BINARY
TEMP
(°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
NOTE: Whenever changing between standard and
extended temperature ranges, be aware that the
temperatures stored in the temperature limit registers are
NOT automatically reformatted to correspond to the new
temperature range format. These temperature limit values
must be reprogrammed in the appropriate binary or
extended binary format.
Both local and remote temperature data use two bytes for
data storage. The high byte stores the temperature with
1°C resolution. The second or low byte stores the decimal
fraction value of the temperature and allows a higher
measurement resolution; see Table 2. The measurement
resolution for the remote channel is 0.0625°C, and is not
adjustable. The measurement resolution for the local
channel is adjustable; it can be set for 0.5°C, 0.25°C,
0.125°C, or 0.0625°C by setting the RES1 and RES0 bits
of the Resolution Register; see the Resolution Register
section.