© 2006 Microchip Technology Inc.

DS21439C-page 7

TC620/TC621

4.0

TYPICAL APPLICATIONS

4.1

Dual Speed Temperature Control

In Figure 4-1, the Dual Speed Temperature Control

uses a TC620 and a TC4469 quad driver. Two of the

drivers of the TC4469 are configured in a simple oscil-

lator. When the temperature is below the LOW TEMP

set point, the output of the driver is OFF. When the tem-

perature exceeds the LOW TEMP set point, the

TC4469 gates the oscillator signal to the outputs of the

driver. This square wave signal modulates the remain-

ing outputs and drives the motor at a low speed. If this

speed cannot keep the temperature below the HIGH

TEMP set point, then the driver turns on continuously

which increases the fan speed to high. The TC620 will

monitor the temperature and only allow the fan to oper-

ate when needed and at the required speed to maintain

the desired temperature. A higher power option can be

designed by adding a resistor and a power MOSFET.

4.2

Temperature Controlled Fan

In the application in Figure 4-2, a high and a low tem-

monitors the ambient temperature and turns the FET

switch on when the temperature exceeds the HIGH

TEMP set point. The fan remains on until the tempera-

ture decreases to the LOW TEMP set point. This

provides the hysteresis. In this application, the fan

turns on only when required.

The TC621 uses an external thermistor to monitor the

ambient temperature. This adds one part, but allows

more flexibility with the location of the temperature

sensor.

FIGURE 4-1:

Dual Speed Temperature Control

FIGURE 4-2:

Temperature Controlled Fan

TC620

2

3

1

5

6

7

+12V

VMOTOR

MOSFET

Fan Motor

50

Ω

Higher Power Option

1N4148

1N4148

8

4

TC4469

2

1

3

5

8

13

4

6

9

10

11

12

14

1M

10k

100k

High

Limit

Low

Limit

Fan Motor

50 pF

Temperature Scale

7

Low Temp.

30 C

˚

High Temp.

50 C

˚

10 µF

0.1 µF

– 30 C (Fan Off)

– 50 C (Fan Low)

– UP (Fan High)

˚

˚

1 µF

0 C

30 C

50 C

˚

˚

˚

TC620

High Temp.

1

2

3

4

8

7

6

5

Low Temp.

+12V

MTP3055E

Fan Motor

TC621

High

Temp.

1

2

3

4

8

7

6

5

Low Temp.

+12V

MTP3055E

Fan Motor

Thermistor

(NTC)