THMC45 Datasheet, PDF (10/16 Pages) Texas Instruments – 5-V AND 3.3-V DC BRUSHLESS FAN MOTOR DRIVER WITH SINGLE WIRE CONTOL

THMC45
5ĆV AND 3.3ĆV DC BRUSHLESS FAN MOTOR DRIVER
WITH SINGLE WIRE CONTROL
SLIS101A − MAY 2001
PRINCIPLES OF OPERATION
locked rotor protection
An internal digital timer is used to monitor the output of the Hall sensor amplifier. When change in commutation
state is not observed via the Hall amplifier inputs within 1 second (typical), t_(RD), the OUTA and OUTB outputs
are disabled for 8 seconds (typical), t_(RETRY). After this period, the THMC45 re-enables the OUTA and OUTB
outputs to automatically restart the motor after a locked rotor condition. When the locked rotor condition
continues to exist, the above process repeats itself until the locked condition is removed or the THMC45 is
powered down (see Figure 6).
Conditioned Hall
Amplifier Output
(Internal)
t(RD)
OUTA, OUTB
Enable
t(RD)
t(RETRY)
t(RETRY)
Figure 6. Typical Locked Rotor Protection Timing Waveforms
open-drain tachometer output (TACH)
The TACH output is an open-drain output that is activated by the output of the Hall sensor comparator output.
When the output of the Hall sensor comparator is high, the TACH output floats high. When the output of the Hall
sensor amplifier is low, the TACH output is pulled low. The resulting output signal has two pulses per revolution
on a four-pole motor.
The TACH output can be used to monitor and measure actual fan speed. It may also be used as part of a
closed-loop speed control system.
thermal shutdown
The THMC45 provides protection against excessive device temperature with a thermal sensor to monitor the
die temperature. In the event that operating or abnormal condition causes the die temperature to exceed t_(SD),
the thermal shutdown threshold (175°C typical), all output drivers are turned off. When t_(SD) has been exceeded,
the die temperature must fall below a hystersis temperature, t_{(SD_HYS)} (15°C typical) before the output drivers
are re-enabled.
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