THMC45

5V AND 3.3V DC BRUSHLESS FAN MOTOR DRIVER

WITH SINGLE WIRE CONTROL

SLIS101A − MAY 2001

1

POST OFFICE BOX 655303

Control With No External Power Drive

Stage Required

to Drive Single Winding, Bipolar Wound,

Two-Phase BLMs

Frequency and Duty Cycle—Suited for

Cooling Fan Applications Requiring

Variable RPM Control to Reduce

Noise/Increase MTBF

Feedback Signal, and Locked Rotor Detect

Feedback Signal

Range

Use of Low Cost Hall Effect Position

Sensor

for Small Fan Circuit Board and Rotor

Housing

description

The THMC45 is a dc brushless motor (BLM) driver and control device designed for use with low-voltage (5 V

or 3.3 V) dc cooling fans having two-phase motors with a single-winding stator. The device includes a

high-efficiency H-bridge pulse width modulation (PWM) drive topology with integrated MOS high-side and

low-side drivers, plus a PWM control input stage to provide the industry’s first efficient speed control solution

inside low-voltage dc cooling fans. This solution eliminates the need for any power drive components on the

main system board, reducing printed-circuit board (PCB) component count, PCB space, and assembly time.

The device also offers two advantages over the other commonly used fan speed control methods, adjustable

external dc supply voltage and adjustable external PWM drive duty cycle.

Unlike the external linear voltage regulation method, the THMC45 high-efficiency PWM drive method adjusts

the level of motor winding power while all other circuitry inside the fan obtains a fixed dc voltage from the fan

supply. This eliminates problems with loss of headroom to internal control circuitry at low fan supply voltage and

the resulting limitation of low-speed operation of 40% that is typically associated with external dc voltage

regulation. The high-efficiency PWM drive method employed by the THMC45 reduces fan supply power

consumption and maximizes full-scale RPM speed over the external linear voltage regulation method, which

has V

× I power loss due to the voltage drop across the regulator.

The THMC45 includes a Hall sensor amplifier and signal conditioning, global thermal shutdown, and locked

rotor protection with automatic restart after a locked rotor condition. The device provides a sleep state to

eliminate the need for an external power component to disconnect the fan from the supply during a system sleep

state. The device also has internal reverse blocking capability to prevent excessive reverse leakage current due

to reversal of power line. The THMC45 is primarily designed for 5-V dc notebook PC cooling fan applications

output, the device is also suitable for applications that require two wires for RPM speed control and tachometer

signal.

Copyright

 2001, Texas Instruments Incorporated

PRODUCTION DATA information is current as of publication date.

Products conform to specifications per the terms of Texas Instruments

standard warranty. Production processing does not necessarily include

testing of all parameters.

Please be aware that an important notice concerning availability, standard warranty, and use in critical applications of

Texas Instruments semiconductor products and disclaimers thereto appears at the end of this data sheet.

PowerPAD is a trademark of Texas Instruments.

PWM

8

7

6

5

1

2

3

4

DGN Package

(TOP VIEW)

H−

OUTA

H+

OUTB

TACH

GND