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TC649VUATR

PWM Fan Speed Controller with Auto-Shutdown and FanSense™ Technology

Microchip Technology 

TC649

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.

+5V

+12V

Analog or Digital

Temperature Data from

One or more Sensors

Open-Drain

(RESET) (Optional)

Output I/O0

R1

+5V

I/O1 (MSB)110 kΩ

CMOS

Outputs I/O2

R2

240 kΩ

R3

360 kΩ

I/O3

CMOS (LSB) R5

Microcontroller

1.5 kΩ

+5V

R6

1 kΩ

1 VIN

CB

VDD 8

.01 µF

2

+ CF

VOUT 7

R4

R7 1µF TC649

18 kΩ 33 kΩ

+5V

R8

18 kΩ

3

CB

VAS

.01µF

4 GND

6

FAULT

5

SENSE

CB

1 µF

R9

800 Ω

+5V

R10

10 kΩ

0.1 µF

Fan

2N2222A

R11

2.2 Ω

GND

INT

FIGURE 5-10:

FIGURE 5-11:

TC649 as a Microcontroller Peripheral.

VRELEASE vs. Temperature

1.0

VDD = 5.5V

0.9

VDD = 5.0V

0.8

0.7

VDD = 4.0V

0.6

0.5

VDD = 3.0V

0.4

0˚C

25˚C

TEMPERATURE

VRELEASE vs. Temperature.

85˚C

DS21449C-page 16

 2002 Microchip Technology Inc.

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