THMC40_11 Datasheet, PDF (7/19 Pages) Texas Instruments – VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS

THMC40, THMC41
VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS
SLIS097 – MARCH 2000
Hall sensor comparator and signal conditioning inputs (H+, H–)
Referring to Figure 1, the THMC40 and THMC41 have an internal Hall sensor comparator allowing the use of
low-cost naked Hall sense elements. The Hall signal conditioning block receives a low-level differential voltage
from the naked Hall position sensor element. The comparator then implements a zero differential voltage
crossing detection with a deglitch time of 25 µs (typical) to reject noise on the Hall signal inputs. Referring to
Figure 2, the PHx drive that was on (low) turns off after the 25-µs deglitch time is reached. Then the opposite
PHx drive turns on after another delay time. This 5-µs (typical) dead time is implemented to prevent both phases
from conducting simultaneously and to allow time for the inductive energy to be snubbed from the phase that
was just turned off. The Hall comparator circuit has an input offset voltage (V_IO) which is not greater than ±7
mV. The common-mode input voltage range is 1 V to 3.5 V (see Figure 2).
Hall Sensor
Waveform
(VH+ - VH–)
VCM
VIO
OFF
PHA Output
Voltage
ON
OFF
PHB Output
Voltage
ON
OFF
TACH Output
Voltage (THMC40)
ON
tDEAD(PHx)
tHALL
5 µs
25 µs
tHALL
tDEAD(PHx)
25 µs
5 µs
Time
Figure 2. Hall Sensor Signal Conditioning Waveforms
Table 1 shows PHA and PHB commutation, and TACH output (THMC40) functionality:
Table 1. PHA and PHB Low-Side Drive Commutation and TACH Functionality
H+
H–
PHA
PHB
TACH
(THMC40)
+
–
High (OFF)
Low (ON)
High (OFF)
–
+
Low (ON)
High (OFF)
Low (ON)
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