Datasheet

LAYOUT CONSIDERATIONS
V+
DXP
DXN
GND
NOTE:Useminimum5miltraceswith5milspacing.
GroundorV+layer
onbottomand/or
top,ifpossible.
1
2
3
4
8
7
6
5
TMP441
0.1mFCapacitor
V+
GND
PCBVia
DXP
DXN
A1
A0
1
2
3
4
8
7
6
5
TMP442
0.1mFCapacitor
V+
GND
PCBVia
DXP1
DXN1
DXP2
DXN2
TMP441
TMP442
SBOS425A – DECEMBER 2008 – REVISED MARCH 2009 .............................................................................................................................................. www.ti.com
Remote temperature sensing on the TMP441/42
measures very small voltages using very low
currents; therefore, noise at the IC inputs must be
minimized. Most applications using the TMP441/42
will have high digital content, with several clocks and
logic level transitions creating a noisy environment.
Layout should adhere to the following guidelines:
1. Place the TMP441/42 as close to the remote
junction sensor as possible.
2. Route the DXP and DXN traces next to each
other and shield them from adjacent signals
through the use of ground guard traces, as
shown in Figure 19 . If a multilayer PCB is used,
bury these traces between ground or V
DD
planes
to shield them from extrinsic noise sources. 5 mil
(0.005 in, or 0,127 mm) PCB traces are
recommended.
3. Minimize additional thermocouple junctions
Figure 19. Suggested PCB Layer Cross-Section
caused by copper-to-solder connections. If these
junctions are used, make the same number and
approximate locations of copper-to-solder
connections in both the DXP and DXN
connections to cancel any thermocouple effects.
4. Use a 0.1 µ F local bypass capacitor directly
between the V+ and GND of the TMP441/42, as
shown in Figure 20 . Minimize filter capacitance
between DXP and DXN to 330pF or less for
optimum measurement performance. This
capacitance includes any cable capacitance
between the remote temperature sensor and
TMP441/42.
5. If the connection between the remote
temperature sensor and the TMP441/42 is less
than 8 in (20,32 cm) long, use a twisted-wire pair
connection. Beyond 8 in, use a twisted, shielded
pair with the shield grounded as close to the
TMP441/42 as possible. Leave the remote sensor
connection end of the shield wire open to avoid
ground loops and 60Hz pickup.
6. Thoroughly clean and remove all flux residue in
and around the pins of the TMP441/42 to avoid
temperature offset readings as a result of leakage
paths between DXP or DXN and GND, or
between DXP or DXN and V+.
Figure 20. Suggested Bypass Capacitor
Placement and Trace Shielding
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