US65 / US66

Two-Coil Low Noise Fan Driver

High Output Current

3901090209

Page 7 of 12

Preliminary Datasheet

Rev 006

Jan/07

It is also possible to run into the 3 different modes as “hard switching”, “internal soft switching” and “external

soft switching”, giving the possibility to adapt the fan design to stringent requirements. For example, high

speed fan generally requires longer output slope compared to usual middle or low speed fan.

Increasing the output slope duration inevitably leads to high power dissipation of the IC itself. However, the

device is well protected against over power dissipation thanks to the integrated thermal shutdown.

10.2 Enhanced Locked Rotor Protection

Specially designed for driving large fans, the Locked Rotor Protection is optimised for low start-up voltage.

At low voltage, fans inevitably starts rotating slower than at higher voltage. Big fans with large inertia have

slow start-up causing a longer first output pulse after power-on. If this pulse duration is longer than the LRP

The US65/66 provides an adequate and simple solution to prevent this by automatically increasing the locked

and automatically double the LRP periods at 5V (0.6s, 3.65s) compared than 12V (0.29s, 1.5s).

11 Performance Graphs

0

1

2

3

4

-40

-20

0

20

40

60

80

100

120

Tj (°C)

VDD = 5V

VDD = 12V

0

1

2

3

4

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

VDD (Volts)

Tj = -40°C

Tj = 25°C

Tj = 85°C

Tj = 125°C

0

1

2

3

4

5

-40

-20

0

20

40

60

80

100

120

Tj (°C)

VDD = 5V

VDD = 12V

0

1

2

3

4

5

3

4

5

6

7

8

9

10

11

12

13

14

15

16

17

18

VDD (Volts)

Tj = -40°C

Tj = 25°C

Tj = 85°C

Tj = 125°C