TC648 datasheet(15/28 Pages) MICROCHIP

15 / 28 page

 2002 Microchip Technology Inc.

DS21448C-page 15

TC648

FIGURE 5-8:

Design Example.

5.8

TC648 as a Microcontroller

Peripheral

In a system containing a microcontroller or other host

intelligence, the TC648 can be effectively managed as

a CPU peripheral. Routine fan control functions can be

performed by the TC648 without processor interven-

tion. The microcontroller receives temperature data

from one or more points throughout the system. It

calculates a fan operating speed based on an algorithm

specifically designed for the application at hand. The

processor controls fan speed using complementary

port bits I/O1 through I/O3.

Resistors R1 through R6 (5% tolerance) form a crude

3-bit DAC that translates the 3-bit code from the

processor's outputs into a 1.6V DC control signal. A

monolithic DAC or digital pot may be used instead of

the circuit shown in Figure 5-9.

With VAS set at 1.8V, the TC648 enters auto-shutdown

when the processor's output code is 000[B]. Output

codes 001[B] to 111[B] operate the fan from roughly

40% to 100% of full speed. An open-drain output from

the processor (I/O0) can be used to reset the TC648

following detection of a fault condition. The OTF output

can be connected to the processor's interrupt input, or

to another I/O pin, for polled operation.

NTC

10 k

Ω

@ 25˚C

20.5 k

Ω

3.83 k

Ω

33 k

Ω

800

Ω

GND

RESET

Shutdown

(Optional)

+12V

+5V

VDD

VIN

VAS

VOUT

µF

TC648

OTF

Fan

Thermal

Fault

0.01

µF

0.01

µF

18 k

Ω

Open-Drain

Device

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