THMC40SOPD datasheet(10/17 Pages) TI

10 / 17 page

THMC40, THMC41

VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS

SLIS097 – MARCH 2000

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PWM duty cycle control voltage (VPWM) – dc control voltage input

The voltage at the VPWM terminal determines the PWM duty cycle of the output (VOUT) to control drive power

to the fan motor, and thus control fan speed (see Figures 3 and 6). The VPWM voltage is internally compared

against the 0.5-V to 2.3-V triangle waveform generated on the COSC terminal. The PWM signal output from this

comparator has a duty cycle proportional to the voltage at VPWM, as shown in Figure 6. The output of this

comparator is used as the PWM input to the VOUT drive stage.

0.2

0.4

0.6

0.8

1.2

100

1.4

1.6

1.8

2.4

2.2

VPWM – Input Voltage – V

RUN STATE

SLEEP

STATE

VSLEEP=0.7 V

VSTART = 0.8 V

Must be exceeded

to enter run state

VOUT Duty Cycle =

(VPWM - 0.5)/1.8 × 100

Figure 6. Relationship of VOUT Duty Cycle, VSTART, and VSLEEP vs VPWM Input Voltage

PWM duty cycle control voltage (VPWM) – digital PWM control input

To allow control of the THMC40 and THMC41 by either a PWM or a dc input control signal, it is recommended

that the fan manufacturer includes a 100-k

Ω, 0.1-µF RC filter between the speed control wire and the VPWM

terminal (see Figure 7). This method allows the end user to control the fan speed with either a PWM signal or

a dc control voltage. Many PC Super I/O ICs and hardware monitoring ICs provide one of the two fan speed

control outputs. Therefore, fans with THMC40 and THMC41 ICs can be used with a wide variety of control

schemes to provide variable fan speed without an external fan drive power stage.

C = 0.1

µF

VPWM

PWM Generator

(Super I/O or

HW Monitor)

PC Motherboard

Inside Cooling Fan

R = 100 k

Ω

THMC40

and

THMC41

Full Speed Option

VFAN

Speed

Control

1 – 10 M

Ω†

1 – 10 M

Ω†

Sleep State Option

† Optional resistors control fan operation with open speed control input.

Figure 7. PWM Input Control With RC Filter Inside the Cooling Fan

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