MAX6643/MAX6644/MAX6645
Automatic PWM Fan-Speed Controllers with
Overtemperature Output
______________________________________________________________________________________ 13
in value. Cable resistance also affects remote-sensor
accuracy. A 1Ω series resistance introduces about
+1/2°C error.
PC Board Layout Checklist
1) Place the MAX6643/MAX6644/MAX6645 as close as
practical to the remote diode. In a noisy environment,
such as a computer motherboard, this distance can
be 4in to 8in or more, as long as the worst noise
sources (such as CRTs, clock generators, memory
buses, and ISA/PCI buses) are avoided.
2) Do not route the DXP lines next to the deflection coils
of a CRT. Also, do not route the traces across a fast
memory bus, which can easily introduce +30°C
error, even with good filtering. Otherwise, most noise
sources are fairly benign.
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 PC board
contamination. 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, PC board-induced ther-
mocouples are not a serious problem. A copper sol-
der thermocouple exhibits 3µV/°C, and it takes
approximately 200µV of voltage error at DXP/GN 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
Pin Configurations
(9 paginas)
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