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In this way, most parasitic thermocouple errors are

swamped out.

Use wide traces. Narrow ones are more inductive and

tend to pick up radiated noise. The 10 mil widths and

spacing recommended on Figure 2 aren't absolutely

necessary (as they offer only a minor improvement in

leakage and noise), but try to use them where practi-

cal.

Keep in mind that copper can't be used as an EMI

shield, and only ferrous materials such as steelwork

will. Placing a copper ground plane between the DXP -

DXN traces and traces carrying high-frequency noise

signals do not help reduce EMI.

PC Board Layout Checklist

n Place the 8017 close to a remote diode.

n Keep traces away from high voltages (+12V bus).

n Keep traces away from fast data buses and CRTs.

n Use recommended trace widths and spacing.

n Place a ground plane under the traces

n Use guard traces flanking DXP and DXN and con-

necting to GND.

n Route two DXPx-DXN pairs independently

n Connect the common DXN as close as possible to

the DXN pin on IC.

n Place the noise filter and the 0.1µF Vcc bypass

capacitors close to the 8017.

Fig 2(a) Connect the common DXN as close as

possible to the DXN pin on IC.

Twisted Pair and Shielded Cables

For remote-sensor distances longer than 8 in., or in

particularly noisy environments, a twisted pair is rec-

ommended. Its practical length is 6 feet to 12 feet (typi-

cal) before noise becomes a problem, as tested in a

noisy electronics laboratory. For longer distances, the

best solution is a shielded twisted pair like that used

for audio microphones. Connect the twisted pair to

DXP and DXN and the shield to GND, and leave the

shield's remote end unterminated.

Excess capacitance at DX_ limits practical remote sen-

sor distances (see Typical Operating Characteristics),

For very long cable runs, the cable's parasitic capaci-

tance often provides noise filtering, so the 2200pF ca-

pacitor can often be removed or reduced in value. Ca-

ble resistance also affects remote-sensor accuracy;

Ω series resistance introduces about + 1°C error.

Low-Power Standby Mode

Standby mode disables the ADC and reduces the sup-

ply-current drain to less than 10µA. Enter standby

mode via the RUN/STOP bit in the configuration byte

ory, and the SMB interface is alive and listening for

reads and writes. This is valid for temperature sensor

only.

Standby mode is not a shutdown mode. With activity

on the SMBus, extra supply current is drawn (see

Typical Operating Characteristics). In software standby

mode, the 8017 can be forced to perform temperature

measurement via the one-shot command, despite the

RUN/STOP bit being high.

Supply-current drain during the 125ms conversion pe-

riod is always about 500µA. Slowing down the conver-

sion rate reduces the average supply current (see

Typical Operating Characteristics). In between conver-

sions, the instantaneous supply current is about

200µA due to the current consumed by the system

resetting circuit.

Reset Immunity Negative-Going VCC Transients

In addition to issuing a reset to the microprocessor (µP)

during power-up, power-down, and brownout conditions,

the 8017 is relatively immune to short duration nega-

tive-going VCC transients (glitches).

Typically, for the 8017, a V CC transient that goes

100mV below the reset threshold and lasts 20µs or

less will not cause a reset pulse. A 0.1µF bypass ca-

pacitor mounted as close as possible to the VCC pin

provides additional transient immunity.

DXP1

DXN

DXP2

DXP1

DXN

DXP2

GND

Chip Boundary

GND

DXP1

DXN

DXP2

DXP1

DXN

SS8017

DXP2

GND

Chip Boundary

GND

DXP

DXN

GND

10 MILS

MINIMUM

10 MILS

GND

DXP

DXN

GND

10 MILS

MINIMUM

10 MILS

Fig 2 (b) Recommended DXP/DXN PC

SS8017

Rev.2.01 6/06/2003

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