Philips Semiconductors

Product data sheet

SA56004X

±1 °C accurate, SMBus-compatible, 8-pin, remote/local

digital temperature sensor with over temperature alarms

2004 Oct 06

19

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 SA56004X is a few microvolts. The following

guidelines are recommended:

1. Place the SA56004X 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 ‘Ideal diode trace layout’,

Figure 18).

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.

input filter capacitor of 2200 pF close to the D+ and D– pins.

6. A shielded twisted pair is recommended if remote sensor is

located several feet away from the temperature sensor. Under

this circumstance, connect the shield of the cable at the device

side to the SA56004X GND pin and leave the shield at the

remote end unconnected to avoid ground loop currents. Also

notice that the series resistance of the cable may introduce

measurement error; 1

Ω can introduce about 0.5 °C.

GND

D+

D–

GND

SL02017

Figure 18. D+ and D– trace layout.

PACKING METHOD

The SA56004X is packed in reels, as shown in Figure 19.

SL01305

TAPE DETAIL

COVER TAPE

CARRIER TAPE

REEL

ASSEMBLY

TAPE

GUARD

BAND

BARCODE

LABEL

BOX

Figure 19. Tape and reel packing method