LM87CIMTX National Semiconductor, LM87CIMTX Datasheet - Page 18

• Manufacturer Part Number: LM87CIMTX
• Description: IC,Data Acquisition System,8-CHANNEL,8-BIT,TSSOP,24PIN,PLASTIC
• Manufacturer: National Semiconductor

Specifications of LM87CIMTX

• Lead Free Status / RoHS Status: Contains lead / RoHS non-compliant

www.national.com
Functional Description
η from part to part. As an example, assume a temperature
sensor has an accuracy specification of
perature of 25˚C and the process used to manufacture the
diode has a non-ideality variation of
accuracy of the temperature sensor at room temperature will
be:
.
The additional inaccuracy in the temperature measurement
caused by η, can be eliminated if each temperature sensor is
calibrated with the remote diode that it will be paired with.
8.5 PCB Layout Recommendations 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 LM87 can cause temperature conversion errors.
The following guidelines should be followed:
1. Place a 0.1 µF power supply bypass capacitor as close
Noise on the digital lines, overshoot greater than V
undershoot less than GND, may prevent successful SMBus
communication with the LM87. SMBus no acknowledge is
the most common symptom, causing unnecessary traffic on
the bus. Although, the SMBus maximum frequency of com-
munication is rather low (400 kHz max) care still needs to be
taken to ensure proper termination within a system with
multiple parts on the bus and long printed circuit board
traces. A lowpass filter, in series with the SMBCLK and
as possible to the V
capacitor as close as possible to the D+ and D− pins.
T
ACC
=
±
3˚C + (
CC
pin and the recommended 2.2 nF
±
1% of 298˚K) =
FIGURE 9. Recommended Diode Trace Layout
±
±
(Continued)
1%. The resulting
3˚C at room tem-
±
6˚C
CC
and
18
2. Ideally, the LM87 should be placed within 10 cm of the
3. Diode traces should be surrounded by a GND guard ring
4. Avoid routing diode traces in close proximity to power
5. Avoid running diode traces close to or parallel to high
6. If it is necessary to cross high speed digital traces, the
7. The ideal place to connect the LM87’s GND pin is as
SMBData, has been added internally to the LM87 for noise
immunity. The lowpass filter has a typical cutoff frequency of
20MHz. Additional noise immunity can be achieved by plac-
ing a resistor (4.7k to 5.1k Ohms) in series with the SMBCLK
input as close to the LM87 as possible. This resistance, in
conjunction with the IC input capacitance, reduces high fre-
quency noise seen at the SMBCLK input and increases the
reliability of communications.
Make sure the traces to the 2.2 nF capacitor are
matched.
Processor diode pins with the traces being as straight,
short and identical as possible.
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.
supply switching or filtering inductors.
speed digital and bus lines. Diode traces should be kept
at least 2 cm. apart from the high speed digital traces.
diode traces and the high speed digital traces should
cross at a 90 degree angle.
close as possible to the Processors GND associated
with the sense diode. For the Pentium II this would be
pin A14.
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