Rainbow Electronics MAX6696 - Manual (Page 17)

Leakage currents from PC board contamination
must be dealt with carefully since a 20M
Ω leakage
path from DXP to ground causes about +1°C error.
If high-voltage traces are unavoidable, connect
guard traces to GND on either side of the DXP-DXN
traces (Figure 5).
4) Route through as few vias and crossunders as pos-
sible to minimize copper/solder thermocouple
effects.
5) Use wide traces when practical.
6) When the power supply is noisy, add a resistor (up
to 47 Ω) in series with V
CC
(see Typical Operating
Circuit).
Twisted-Pair and Shielded Cables
Use a twisted-pair cable to connect the remote sensor
for remote-sensor distances longer than 8in or in very
noisy environments. Twisted-pair cable lengths can be
between 6ft and 12ft before noise introduces excessive
errors. For longer distances, the best solution is a
shielded twisted pair like that used for audio micro-
phones. For example, Belden #8451 works well for dis-
tances up to 100ft in a noisy environment. At the
device, connect the twisted pair to DXP and DXN and
the shield to GND. Leave the shield unconnected at the
remote sensor.
For very long cable runs, the cable’s parasitic capaci-
tance often provides noise filtering, so the 2200pF
capacitor can often be removed or reduced in value.
Cable resistance also affects remote-sensor accuracy.
For every 1
Ω of series resistance the error is approxi-
mately +1/2°C.
Chip Information
TRANSISTOR COUNT: 22,964
PROCESS: BiCMOS
MAX6695/MAX6696
Dual Remote/Local Temperature Sensors with
SMBus Serial Interface
______________________________________________________________________________________ 17
MINIMUM
10 mils
10 mils
10 mils
10 mils
GND
DXN
DXP
GND
Figure 5. Recommended DXP-DXN PC Traces
Typical Operating Circuits (continued)
CLOCK
DATA
TO SYSTEM
SHUTDOWN
STBY
RESET GND ADD1
OT2
SMBCLK
OT1
SMBDATA
V CC
INTERRUPT
TO
µP
0.1 µF
DXN
DXP1
47 Ω
10k Ω
EACH
ALERT
+3.3V
ADD0
MAX6696
CPU
2N3906
DXP2
TO CLOCK
THROTTLING