MAX6643/MAX6644/MAX6645
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
______________________________________________________________________________________ 13
3) Route the DXP and GND traces parallel and close to
each other, away from any high-voltage traces such
as +12VDC. Avoid leakage currents from PCB conta-
mination. A 20MΩ leakage path from DXP to ground
causes approximately +1°C error.
4) Route as few vias and crossunders as possible to
minimize copper/solder thermocouple effects.
5) When introducing a thermocouple, make sure that
both the DXP and the GND paths have matching
thermocouples. In general, PCB-induced thermocou-
ples are not a serious problem. A copper solder ther-
mocouple exhibits 3µV/°C, and it takes
approximately 200µV of voltage error at DXP/GND to
cause a +1°C measurement error, so most parasitic
thermocouple errors are swamped out.
6) Use wide traces. Narrow traces are more inductive
and tend to pick up radiated noise. The 10-mil widths
and spacings are recommended, but are not
absolutely necessary (as they offer only a minor
improvement in leakage and noise), but use them
where practical.
7) Placing an electrically clean copper ground plane
between the DXP traces and traces carrying high-
frequency noise signals helps reduce EMI.
Chip Information
TRANSISTOR COUNT: 12,518
PROCESS: BiCMOS
