THMC45_13 Datasheet, PDF (6/15 Pages) Texas Instruments – 5-V AND 3.3-V DC BRUSHLESS FAN MOTOR DRIVER WITH SINGLE WIRE CONTROL

THMC45
5ĆV AND 3.3ĆV DC BRUSHLESS FAN MOTOR DRIVER
WITH SINGLE WIRE CONTROL
SLIS101A − MAY 2001
PRINCIPLES OF OPERATION
Hall sensor amplifier inputs (H+, H−)
The THMC45 has an internal Hall sensor amplifier with signal conditioning to allow the use of low-cost Hall
sensors requiring no external components for noise filtering. The Hall signal conditioning block receives a
low-level differential voltage from the Hall position sensor and implements a zero differential voltage crossing
detection with a de-glitch time of 25 µs (typical), t_(de-glitch), to reject noise on the Hall signal inputs. Refer to
Figure 1, the OUTA output changes from sourcing current to sinking current after the 25-µs de-glitch time.
Likewise, the OUTB output changes from sinking current to sourcing current after the 25-µs de-glitch time. The
Hall amplifier circuit has an input offset voltage, V_IO, not greater than ±13 mV when V_PWR is between 4.5 V and
5.5 V. The common mode input voltage range is 1 V to 3.5 V when V_PWR is between 4.5 V and 5.5 V.
Differential Hall
Signal (H+ − H−)
Conditioned Hall
Amplifier Output
(Internal)
t(de-glitch)
t(de-glitch)
t(de-glitch)
PWM Input
OUTA
OUTB
Figure 1. Hall Sensor Signal Conditioning Waveform and OUTA/OUTB Commutation
Illustrated in truth table format, Table 1 shows OUTA and OUTB commutation and PWM.
Table 1. OUTA and OUTB Low-Side Drive Commutation
H+
H− OUTA OUTB
H
L
H
PWM
L
H
PWM
H
H-bridge motor drive outputs (OUTA, OUTB)
Using an H-bridge to drive a bipolar wound, two-phase BLM provides several advantages for dc fans over the
unipolar-wound motor commonly driven by two commutated low-side switches. A bipolar-wound motor has only
two connections; hence, the H-bridge drive topology requires only two output terminals and two traces are
needed on the fan PCB. A bipolar-wound stator has a single-wire winding which is simpler to manufacture, and
thus increases reliability and reduces manufacturing time. All factors combine to allow a smaller diameter fan
center hub, and thus higher blade area for increased airflow on a given fan frame size. Generally, an H-bridge
drive method with bipolar-wound stator increases fan motor torque density over a typical unipolar drive method.
The H-bridge drive method also eliminates the need for snubbing inductive energy at commutation transitions
and allows for recirculation of winding current to maintain energy in the motor while PWM switching occurs.
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