f75385 Feature Integration Technology Inc., f75385 Datasheet - Page 10

• Manufacturer Part Number: f75385
• Description: ?1o C Accuracy Temperature Sensor Ic Datasheet
• Manufacturer: Feature Integration Technology Inc.

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Place the F75385 as close as practical to the remote sensing diode. In noisy environments, such as a computer
main-board, the distance can be 4 to 8 inches. (typ). This length can be increased if the worst noise sources are
avoided. Noise sources generally include clock generators, power control circuit, CRTs, memory buses and
PCI/ISA bus etc.
Route the D+ and D- tracks close together, in parallel, with grounded guard tracks on each side. Provide a ground
plane under the tracks if possible. Do not route D+ & D- lines next to the deflection coil of the CRT. And also don’t
route the trace across fast digital signals which can easily induce bigger error.
Use wide tracks to minimize inductance and reduce noise pickup. 10 mil track minimum width and spacing is
recommended.
Try to minimize the number of copper/solder joints, which can cause thermocouple effects. Where copper/solder
joints are used, make sure that they are in both the D+ and D- path and at the same temperature. Thermocouple
effects should not be a major problem as 1
thermocouple exhibits 3µV/ ℃ , and takes about 200µV of the voltage error at D+ & D- to cause a 1 ℃
measurement error. Adding a few thermocouples causes a negligible error.
Place a 0.1µF bypass capacitor close to the V
filter capacitors across D+, D- close to the F75385.
If the distance to the remote sensor is more than 8 inches, the use of twisted pair cable is recommended. It will
work up to around 6 to 12 feet.
Because the measurement technique uses switched current sources, excessive cable and/or filter capacitance
will affect the measurement accuracy. When using long cables, the filter capacitor may be reduced or removed.
Cable resistance can also induce errors. 1 Ω series resistance introduces about 0.5
MINIMUM
10MILS
10MILS
℃
corresponds to about 200µV
DD
-7-
pin. In very noisy environments, place an external 2200pF input
GND
DXP
DXN
GND
. It means that a copper-solder
10MILS
10MILS
℃
er
ror.
July 2006
V0.21P