THMC40_11 Datasheet, PDF (10/19 Pages) Texas Instruments – VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS

THMC40, THMC41
VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS
SLIS097 – MARCH 2000
PWM duty cycle control voltage (V_PWM) – dc control voltage input
The voltage at the V_PWM terminal determines the PWM duty cycle of the output (V_OUT) to control drive power
to the fan motor, and thus control fan speed (see Figures 3 and 6). The V_PWM voltage is internally compared
against the 0.5-V to 2.3-V triangle waveform generated on the C_OSC terminal. The PWM signal output from this
comparator has a duty cycle proportional to the voltage at V_PWM, as shown in Figure 6. The output of this
comparator is used as the PWM input to the V_OUT drive stage.
100
90
80
70
60
SLEEP
STATE
50
VOUT Duty Cycle =
(VPWM - 0.5)/1.8 × 100
RUN STATE
40
30
VSLEEP=0.7 V
20
10
VSTART = 0.8 V
Must be exceeded
to enter run state
0
0
0.2 0.4 0.6 0.8 1
1.2 1.4 1.6 1.8 2 2.2 2.4
VPWM – Input Voltage – V
Figure 6. Relationship of V_OUT Duty Cycle, V_START, and V_SLEEP vs V_PWM Input Voltage
PWM duty cycle control voltage (V_PWM) – 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-kΩ, 0.1-µF RC filter between the speed control wire and the V_PWM
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.
PC Motherboard
VFAN
Inside Cooling Fan
Full Speed Option
PWM Generator
(Super I/O or
HW Monitor)
Speed
Control
1 – 10 MΩ†
R = 100 kΩ VPWM
1 – 10 MΩ^†
C = 0.1 µF
THMC40
and
THMC41
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
10
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265