Rainbow Electronics LM41 - Manual (Page 26)

3.0 Application Hints
(Continued)
3. Ideally, the LM41 should be placed within 10cm of the
Processor diode pins with the traces being as straight,
short and identical as possible. Trace resistance of 0.7
Ω
can cause as much as 1˚C of error. This error can be
compensated for by adding or subtracting an offset to
the remote temperature reading(s).
4. Diode traces should be surrounded by a GND guard ring
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.
5. Avoid routing diode traces in close proximity to power
supply switching or filtering inductors.
6. Avoid running diode traces close to or parallel to high
speed digital and bus lines. Diode traces should be kept
at least 2cm apart from the high speed digital traces.
7. If it is necessary to cross high speed digital traces, the
diode traces and the high speed digital traces should
cross at a 90 degree angle.
8. The ideal place to connect the LM41’s GND pin is as
close as possible to the Processors GND associated
with the sense diode.
9. Leakage current between D+ and GND should be kept
to a minimum. Seventeen nano-amperes of leakage can
cause as much as 0.2˚C of error in the diode tempera-
ture reading (see curve in Section Typical Performance
Characteristics). Keeping the printed circuit board as
clean as possible will minimize leakage current.
The SensorPath Bus is less sensitive to noise than its pre-
decessor the SMBus due to the inherent filtering present in
the pulse-width encoding of the data. Care still needs to be
taken such that induced noise is analyzed and minimized.
SensorPath Bus corrupt data is the most common symptom
for noise coupled in SWD. A no-ACK is the symptom for
noise coupled into the Device Number Select pin (ADD). An
RC lowpass filter as well as a debouncing circuit are in-
cluded in the LM41 that filter noise spikes less than 2.5 µsec
in duration on the SWD signal.
LM41
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