Datasheet
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LM95245
SNIS148G –OCTOBER 2007–REVISED MARCH 2013
www.ti.com
APPLICATIONS HINTS
The LM95245 can be applied easily in the same way as other integrated-circuit temperature sensors, and its
remote diode sensing capability allows it to be used in new ways as well. It can be soldered to a printed circuit
board, and because the path of best thermal conductivity is between the die and the pins, its temperature will
effectively be that of the printed circuit board lands and traces soldered to the LM95245's pins. This presumes
that the ambient air temperature is almost the same as the surface temperature of the printed circuit board; if the
air temperature is much higher or lower than the surface temperature, the actual temperature of the LM95245 die
will be at an intermediate temperature between the surface and air temperatures. Again, the primary thermal
conduction path is through the leads, so the circuit board temperature will contribute to the die temperature much
more strongly than will the air temperature.
To measure temperature external to the LM95245's die, use a remote diode. This diode can be located on the
die of a target IC, allowing measurement of the IC's temperature, independent of the LM95245's temperature. A
discrete diode can also be used to sense the temperature of external objects or ambient air. Remember that a
discrete diode's temperature will be affected, and often dominated, by the temperature of its leads. Most silicon
diodes do not lend themselves well to this application. It is recommended that an MMBT3904 transistor base-
emitter junction be used with the collector tied to the base. Accuracy using the MMBT3904 is not guaranteed. For
applications requiring the use of the MMBT3904 use the LM95235.
The LM95245's BJT Beta Compensation TruTherm technology allows accurate sensing of integrated thermal
diodes, such as those found on most processors.
The LM95245 has been optimized to measure the remote thermal diode integrated in a typical Intel processor on
45 nm, 65 nm or 90 nm process. Using the Remote Diode Model Select register the remote inputs must be
assigned to sense a typical Intel processor on 45nm, 65 nm or 90 nm process. The typical performance of the
LM95245 with these processors is shown in Figure 18. The Remote Offset register can be used to compensate
for temperature errors further.
Figure 18. LM95245 Typical Performance with a Variety of Intel Processors
DIODE NON-IDEALITY
Diode Non-Ideality Factor Effect on Accuracy
When a transistor is connected as a diode, the following relationship holds for variables V
BE
, T and I
F
:
where
•
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