TC646 Просмотр технического описания (PDF) - Microchip Technology

Номер в каталоге

Компоненты Описание

производитель

TC646

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

Microchip Technology 

TC646

Design Example

Step 1. Calculate R1 and R2 based on using an NTC

having a resistance of 10 kΩ at TMIN (25°C)

and 4.65 kΩ at TMAX (45°C) (See Figure 5-9).

R1 = 20.5 kΩ

R2 = 3.83 kΩ

Step 2. Set auto-shutdown level VAS = 1.8V.

Limit the divider current to 100 µA from which

R5 = 33 kΩ

R6 = 18 kΩ

Step 3. Design the output circuit.

Maximum fan motor current = 250 mA. Q1

beta is chosen at 50 from which R7 = 800 Ω.

+5V

Reset

Shutdown

Open-Drain

Device

(Optional)

R1

20.5 kΩ

R2

3.83 kΩ

+5V

NTC

10 kΩ

CB

1 µF

@ 25˚C

1

VIN

8

VDD

CB

0.01 µF

4

GND

6

FAULT

+5V

R5

33 kΩ

R6

18 kΩ

3 VAS

CB

0.01 µF

2

CF

C1

1 µF

TC646

7

VOUT

5

SENSE

+12V

Fan

Fan/Thermal

Fault

Q1

R7

800Ω

CSENSE

0.1 µF

RSENSE

2.2Ω

FIGURE 5-9:

Design Example.

5.8 TC646 as a Microcontroller

Peripheral

In a system containing a microcontroller or other host

intelligence, the TC646 can be effectively managed as

a CPU peripheral. Routine fan control functions can be

performed by the TC646 without controller intervention.

The microcontroller receives temperature data from

one or more points throughout the system. It calculates

a fan operating speed based on an algorithm specifi-

cally designed for the application at hand. The proces-

sor controls fan speed using complementary port bits

I/O1 through I/O3. Resistors R1 through R6 (5% toler-

ance) form a crude 3-bit DAC that translates the 3-bit

code from the processor's outputs into a 1.6V DC con-

trol 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 TC646 enters auto-shutdown

when the controller'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 TC646

following detection of a fault condition. The FAULT out-

put can be connected to the controller's interrupt input,

or to another I/O pin, for polled operation.

DS21446C-page 16

 2002 Microchip Technology Inc.

Share Link: