THMC45

5V AND 3.3V DC BRUSHLESS FAN MOTOR DRIVER

WITH SINGLE WIRE CONTROL

SLIS101A − MAY 2001

7

POST OFFICE BOX 655303

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

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

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

Motor

OUTA

GND

PWM

OFF

ON

OUTB

OUTA

H

H+

H

H−

L

OUTB

PWM

M1

M2

M3

M4

M1

M2

PWM

PWM tON

I(DRIVE)

Motor

OUTA

GND

PWM

OFF

ON

OUTB

M3

M4

PWM

I(RECIRCULATE)

PWM tOFF

a) A to B Current Direction

VPWR

VPWR

Motor

OUTA

GND

PWM

OFF

ON

OUTB

OUTA

PWM

H+

L

H−

H

OUTB

H

M1

M2

M3

M4

M1

M2

PWM tON

I(DRIVE)

Motor

OUTA

GND

PWM

OFF

ON

OUTB

M3

M4

PWM

I(RECIRCULATE)

PWM tOFF

PWM

b) B to A Current Direction

VPWR

VPWR

Figure 2. H-Bridge PWM Drive With Synchronous Rectification