TC642 datasheet(16/28 Pages) MICROCHIP

16 / 28 page

TC642

DS21444C-page 16

 2002 Microchip Technology Inc.

5.8

TC642 as a Microcontroller

Peripheral

In a system containing a microcontroller or other host

intelligence, the TC642 can be effectively managed as

a CPU peripheral. Routine fan control functions can be

performed by the TC642 without processor intervention.

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 sig-

nal. A monolithic DAC or digital pot may be used

instead of the circuit shown in Figure 5-10.

With VMIN set to 1.8V, the TC642 has a minimum

operating speed of approximately 40% of full rated

speed 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 TC642 following detection of a fault condition. The

FAULT output can be connected to the processor's

interrupt input, or to an I/O pin, for polled operation.

FIGURE 5-10:

TC642 as a Microcontroller Peripheral.

TC642

VIN

VMIN

GND

VDD

VOUT

FAULT

SENSE

(Optional)

(MSB)

110 k

Ω

240 k

Ω

360 k

Ω

(LSB)

1.5 k

Ω

+5V

1 k

Ω

18 k

Ω

33 k

Ω

+5V

18 k

Ω

.01

µF

.01

µF

Fan

+12V

+5V

µF

800

Ω

+5V

R10

10 k

Ω

0.1

µF

2N2222A

R11

2.2

Ω

(RESET)

CMOS

Microcontroller

+5V

Analog or Digital

Temperature

Data from one or

more Sensors

I/O0

I/O1

I/O2

I/O3

INT

GND

CMOS

Outputs

Open-drain

Outputs

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