LM741J883 National Semiconductor, LM741J883 Datasheet

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LM741J883

Manufacturer Part Number
LM741J883
Description
CDIP
Manufacturer
National Semiconductor
Datasheet

Specifications of LM741J883

Date_code
03+

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© 2002 National Semiconductor Corporation
Tiny Temperature Sensors
for Portable Systems
The last year has seen the introduction of silicon tempera-
ture sensors in revolutionary small packages, ideal for por-
table systems. This brief will discuss trade-offs in accuracy,
as well as how to choose between thermistors and analog
output IC temperature sensors. Figure 1 shows the output
voltage transfer function of various analog output tempera-
ture sensors. These sensors are available in tiny packages
like the SC70 and the 4-bump micro SMD. The LM20 is the
smallest, lowest power (10µA max) analog output tempera-
ture sensor National Semiconductor has released and is
available in the SC70 and micro SMD packages. The LM70
and LM74 are MICROWIRE/SPI compatible digital tempera-
ture sensors and are available in the LLP and 8-bump micro
SMD packages, respectively. The LM70 and LM74 have
resolutions of 0.125˚C and 0.0625˚C, respectively. The
LM74 is the most accurate of the two, with an accuracy of
better than
The
temperature-to-voltage transfer functions of silicon tempera-
ture sensors with that of an NTC thermistor.
Thermistors come in a variety of packages ranging from
probes to beads. However ICs have surface mount packag-
ing equivalent to thermistors, as in the LM20 micro SMD.
FIGURE 1. Comparison of analog temperature
curves
±
1.25˚C.
shown
sensors to thermistors
in
Figure
AN200546
1
compare
20054601
the
National Semiconductor
Application Note 1256
September 2002
Thermistors, when biased ratiometrically (as shown in Figure
2), have the advantage of not requiring an accurate or stable
voltage reference in the system. In ratiometric operation, the
error introduced by the reference is cancelled out. If ratio-
metric operation is not possible, for instance when the ADC
reference voltage is in an ASIC and is not pinned out, using
ICs like the LM20 will result in better total system accuracy.
The LM20 draws only 10µA of current while the current
drawn by the thermistor circuit depend on the value of R.
We
NTH5G10P/16P33B103F. This thermistor has an accuracy
of 1% at 25˚C. The evaluation used ADCs with various
resolutions to examine the overall system accuracy which
depends on the resolution of the ADC, the ADC’s errors
(gain, offset and nonlinearity or TUE, total unadjusted error)
and the resolution of the compensation table.
Figure 3 shows the voltage applied at the ADC input for the
thermistor circuit shown in Figure 2. Note that the ADC input
voltage decreases logarithmically with increasing tempera-
ture. The 97.6k resistor optimizes the power dissipation
analyzed
FIGURE 2. Connecting a thermistor or
a
an LM20 to an ADC
specific
thermistor,
www.national.com
the
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