THMC40, THMC41

VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS

SLIS097 – MARCH 2000

7

POST OFFICE BOX 655303

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

mV. The common-mode input voltage range is 1 V to 3.5 V (see Figure 2).

tDEAD(PHx)

VCM

PHA Output

Voltage

PHB Output

Voltage

OFF

ON

OFF

ON

VIO

5

µs

tHALL

25

µs

tDEAD(PHx)

tHALL

25

µs

5

µs

Time

TACH Output

Voltage (THMC40)

OFF

ON

Hall Sensor

Waveform

(VH+ - VH–)

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)