Philips Semiconductors Product data sheet
NE1619HECETA4 Temperature and voltage monitor
2004 Oct 05
16
Printed Circuit Board layout considerations
Care must be taken in PCB layout to minimize noise induced at the
remote temperature sensor inputs, especially in extremely noisy
environments, such as a computer motherboard. Noise induced in
the traces running between the device sensor inputs and the remote
diode can cause temperature conversion errors. Typical sensor
signal levels to the NE1619 is a few microvolts. The following
guidelines are recommended:
1. Place the NE1619 as close as possible to the remote sensor. It
can be from 4 to 8 inches, as long as the worst noise sources
such as clock generator, data and address buses, CRTs are
avoided.
2. Route the D+ and D– lines parallel and close together with
ground guards enclosing them (see Figure 14).
3. Leakage currents due to PC board contamination must be
considered. Error can be introduced by these leakage currents.
4. Use wide traces to reduce inductance and noise pickup. Narrow
traces more readily pickup noise. The minimum width of 10 mil
and space of 10 mil are recommended.
GND
D+
D–
GND
SL01218
Figure 14. PCB layout for D+ and D–
5. Place a bypass capacitor of 100 nF close to the V
DD
pin and an
input filter capacitor of 2200 pF close to the D+ and D– pins.
6. If the remote sensor is operating in a noisy environment and
located several feet away from the NE1619, a shielded twisted
pair cable is recommended. Make sure the shield of the cable is
connected to the NE1619 ground pin, and leave the shield at the
remote end unconnected. Shield connecting to ground of both
ends could create a ground loop (refer to Figure 15) and defeat
the purpose of the shielded cable. Also, cold soldered joints and
damaged cable could introduce series resistance and reslult in
measurement error. For instance, a 1 Ω resistance can introduce
a change of temperature of about 0.5 °C.
SL02156
D+
D–
NE1619
GND
REMOTE
SENSOR
SHIELDED TWISTED PAIR
Figure 15. Using shielded twisted pair
