THMC40 Datasheet, PDF (11/17 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) – digital PWM control input (continued)
Figure 8 illustrates the relationship between V_OUT output duty-cycle and a 0–3.3-V digital PWM input control
signal.
100
90
VOUT % =((3.3 V ×
80
(Input%÷100)-0.5)÷1.8) × 100
70
60
SLEEP
STATE
50
RUN STATE
40
30 ^VSLEEP=21%
20
VSTART = 24%
10
Must be exceeded to
enter run state
0
0
10
20
30
40
50
60
70
80
90
100
3.3-V Duty Cycle Input to RC Filter
Figure 8. Relationship of V_OUT Duty Cycle, V_SLEEP, V_START vs 0–3.3 V PWM Input Duty Cycle
sleep/run state
Sleep-state and run-state modes are provided, as illustrated in Figures 6 and 8. The sleep state is intended to
minimize V_PWR (fan) supply current requirements (300 µA typical) when cooling fan operation is not required.
This feature is especially beneficial for PC OEMs needing to meet the instantly available PC requirements
without the use of additional external circuitry.
The sleep state is engaged when the V_PWM input voltage is below the V_SLEEP threshold (0.7 V typical, 11.1%
duty cycle). During the sleep state, all output drivers are turned off and any unused circuits are powered down
to minimize current drain. Once sleep state is engaged, V_PWM must exceed the V_START threshold (0.8 V typical,
17% duty cycle) to disable the sleep state and enter the run state, allowing the motor to be driven. Once the
run state is engaged, outputs V_OUT, PHA, and PHB are active and the V_PWM voltage can be decreased to obtain
minimum fan speed down to the V_SLEEP threshold. This procedure allows the user to overcome initial motor
stiction with a PWM duty cycle of 17% to avoid the possibility of false locked rotor detection during initial start-up.
See Figure 6 for the V_PWM input voltage relationship to sleep mode and V_OUT duty cycle.
A control device with a voltage range of 0 V to 2.5 V is recommended to provide the adjustable V_PWM reference
voltage to the THMC40 and THMC41. A 2.5-V DAC is an optimal choice as the controlling circuitry, whether as
a stand-alone device, or as an integrated function in a multiple-function device. Using a control device without
a minimum 0.5-V to 2.3-V range reduces the RPM control range of the fan motor and may not allow duty-cycle
settings of 0% and/or 100%.
thermal shutdown
The THMC40 and THMC41 provide protection against excessive device temperature with a thermal sensor that
monitors the die temperature. Should some operating or abnormal condition cause the die temperature to
exceed T_TSD, the thermal shutdown threshold (165°C typical), all output drivers are turned off. Once T_TSD has
been exceeded, the die temperature must fall below a hysteresis temperature (typical T_TSD –15°C) before the
output drivers are re-enabled.
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