TC649 datasheet(16/28 Pages) MICROCHIP

16 / 28 page

TC649

DS21449C-page 16

 2002 Microchip Technology Inc.

5.8

TC649 as a Microcontroller

Peripheral

In a system containing a microcontroller or other host

intelligence, the TC649 can be effectively managed as

a CPU peripheral. Routine fan control functions can be

performed by the TC649 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

this 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 5-10.

With VAS set at 1.8V, the TC649 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 TC649

following detection of a fault condition. The FAULT out-

put can be connected to the processor's interrupt input

or to another I/O pin for polled operation.

FIGURE 5-10:

TC649 as a Microcontroller Peripheral.

FIGURE 5-11:

VRELEASE vs. Temperature.

CMOS

Microcontroller

TC649

VIN

VAS

GND

VDD

VOUT

SENSE

+5V

Analog or Digital

Temperature Data from

One or more Sensors

I/O1

I/O2

I/O3

INT

GND

(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

.01µF

1µF

.01 µF

CMOS

Outputs

Open-Drain

Output

Fan

+12V

+5V

1 µF

800

Ω

+5V

R10

10 k

Ω

0.1 µF

2N2222A

R11

2.2

Ω

(RESET)

FAULT

I/O0

VRELEASE vs. Temperature

0˚C

25˚C

TEMPERATURE

85˚C

VDD = 3.0V

VDD = 4.0V

VDD = 5.0V

VDD = 5.5V

1.0

0.9

0.8

0.7

0.6

0.5

0.4

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