THMC45 datasheet(7/15 Pages) TI1

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THMC45

5V AND 3.3V DC BRUSHLESS FAN MOTOR DRIVER

WITH SINGLE WIRE CONTROL

SLIS101A − MAY 2001

POST OFFICE BOX 655303

• DALLAS, TEXAS 75265

PRINCIPLES OF OPERATION

H-bridge motor drive outputs (OUTA, OUTB) (continued)

Figures 2a and 2b show THMC45 H-bridge motor drive states with stator winding current being driven from

OUTA to OUTB and from OUTB to OUTA, respectively, based on the Hall sensor commutation state. As shown

during tON, PWM signal is high and the drive current is from VPWR through the activated switches and motor

to GND. PWM occurs on the low side, and the stator winding inductive current recirculates on the high side

during tOFF and PWM signal is low (see Figure 3 for motor current waveform). Recirculation of inductive current

through the high-side switches during tOFF, known as synchronous rectification, improves power conversion

efficiency by maintaining energy in the stator winding and results in a continuous dc current level.

Motor

OUTA

GND

PWM

OFF

OUTB

OUTA

H+

H−

OUTB

PWM

PWM tON

I(DRIVE)

Motor

OUTA

GND

PWM

OFF

OUTB

PWM

I(RECIRCULATE)

PWM tOFF

a) A to B Current Direction

VPWR

Motor

OUTA

GND

PWM

OFF

OUTB

OUTA

PWM

H+

H−

OUTB

PWM tON

I(DRIVE)

Motor

OUTA

GND

PWM

OFF

OUTB

PWM

I(RECIRCULATE)

PWM tOFF

PWM

b) B to A Current Direction

VPWR

Figure 2. H-Bridge PWM Drive With Synchronous Rectification

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