LM83CIMQA National Semiconductor, LM83CIMQA Datasheet - Page 17

• Manufacturer Part Number: LM83CIMQA
• Description: Temperature Sensor IC
• Manufacturer: National Semiconductor

Specifications of LM83CIMQA

• Peak Reflow Compatible (260 C): No
• Ic Function: Temperature Sensor IC
• Supply Voltage Max: 3.6V
• Leaded Process Compatible: No
• Mounting Type: Surface Mount
• Operating Temperature Range: -40°C To +125°C
• Temperature Sensor Function: Temp Sensor
• Interface Type: Serial (2-Wire)
• Output Type: Digital
• Operating Temperature (min): -40C
• Operating Temperature (max): 125C
• Operating Temperature Classification: Automotive
• Operating Supply Voltage (min): 3V
• Operating Supply Voltage (typ): 3.3V
• Operating Supply Voltage (max): 3.6V
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant
• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

4.0 Application Hints
The LM83 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 cir-
cuit board lands and traces soldered to the LM83’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 sur-
face temperature, the actual temperature of the of the LM83
die will be at an intermediate temperature between the sur-
face and air temperatures. Again, the primary thermal con-
duction path is through the leads, so the circuit board tem-
perature will contribute to the die temperature much more
strongly than will the air temperature.
To measure temperature external to the LM83’s die, use a
remote diode. This diode can be located on the die of a tar-
get IC, allowing measurement of the IC’s temperature, inde-
pendent of the LM83’s temperature. The LM83 has been op-
timized to measure the remote diode of a Pentium II
processor as shown in Figure 9 . 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 af-
fected, and often dominated, by the temperature of its leads.
Most silicon diodes do not lend themselves well to this appli-
cation. It is recommended that a 2N3904 transistor base
emitter junction be used with the collector tied to the base.
A diode connected 2N3904 approximates the junction avail-
able on a Pentium microprocessor for temperature measure-
ment. Therefore, the LM83 can sense the temperature of this
diode effectively.
3.1 ACCURACY EFFECTS OF DIODE NON-IDEALITY
FACTOR
The technique used in today’s remote temperature sensors
is to measure the change in V
points of a diode. For a bias current ratio of N:1, this differ-
ence is given as:
Pentium or 3904 Temperature vs LM83 Temperature
Reading
BE
at two different operating
DS101058-15
17
where:
The temperature sensor then measures V
to digital data. In this equation, k and q are well defined uni-
versal constants, and N is a parameter controlled by the tem-
perature sensor. The only other parameter is , which de-
pends on the diode that is used for measurement. Since
not be distinguished from variations in temperature. Since
the non-ideality factor is not controlled by the temperature
sensor, it will directly add to the inaccuracy of the sensor. For
the Pentium II Intel specifies a
to part. As an example, assume a temperature sensor has
an accuracy specification of
˚C and the process used to manufacture the diode has a
non-ideality variation of
temperature sensor at room temperature will be:
The additional inaccuracy in the temperature measurement
caused by , can be eliminated if each temperature sensor is
calibrated with the remote diode that it will be paired with.
3.2 PCB LAYOUT for MINIMIZING NOISE
In a noisy environment, such as a processor mother board,
layout considerations are very critical. Noise induced on
traces running between the remote temperature diode sen-
sor and the LM83 can cause temperature conversion errors.
The following guidelines should be followed:
1. Place a 0.1 µF power supply bypass capacitor as close
2. The recommended 2.2nF diode bypass capacitor actu-
3. Ideally, the LM83 should be placed within 10cm of the
4. Diode traces should be surrounded by a GND guard ring
5. Avoid routing diode traces in close proximity to power
•
• q is the electron charge,
• k is the Boltzmann’s constant,
• N is the current ratio,
• T is the absolute temperature in ˚K.
V
BE
manufactured on,
as possible to the V
capacitor as close as possible to the D+ and D− pins.
Make sure the traces to the 2.2nF capacitor are
matched.
ally has a range of 200pF to 3.3nF. The average tem-
perature accuracy will not degrade. Increasing the ca-
pacitance will lower the corner frequency where
differential noise error affects the temperature reading
thus producing a reading that is more stable. Con-
versely, lowering the capacitance will increase the cor-
ner frequency where differential noise error affects the
temperature reading thus producing a reading that is
less stable.
Processor diode pins with the traces being as straight,
short and identical as possible. Trace resistance of 1
can cause as much as 1˚C of error.
to either side, above and below if possible. This GND
guard should not be between the D+ and D− lines. In the
event that noise does couple to the diode lines it would
be ideal if it is coupled common mode. That is equally to
the D+ and D− lines.(See Figure 10 )
supply switching or filtering inductors.
is the non-ideality factor of the process the diode is
is proportional to both
T
ACC
=
±
3˚C + (
CC
±
1%. The resulting accuracy of the
±
pin and the recommended 2.2 nF
1% of 298 ˚K) =
±
3 ˚C at room temperature of 25
and T, the variations in
±
1% variation in
BE
±
6 ˚C.
and converts
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