THMC45

5V AND 3.3V DC BRUSHLESS FAN MOTOR DRIVER

WITH SINGLE WIRE CONTROL

SLIS101A − MAY 2001

5

POST OFFICE BOX 655303

PARAMETER

TEST CONDITIONS

MIN

TYP

MAX

UNIT

fPWM

PWM input frequency

18

30

50

kHz

t(SLEEP)

Time to enter sleep state after no transitions on PWM

terminal

See Figure 5

2

ms

t(PW)

Tachometer signal pulse width

See Figure 4

1

µs

td

Delay after rising edge of PWM input for TACH signal

See Figure 4

1

µs

tRD

Locked rotor detect delay time

See Figure 6

1

s

tRETRY

Auto-restart delay time

See Figure 6

8

s

t(de-glitch)

Hall transition valid time for commutation to occur

See Figures 1 and 4

25

µs

t(PWM_de-glitch)

De-glitch time for PWM input to prevent TACH current

pulses from falsely triggering PWM

See Figure 5

25

µs

tf(OUT)

OUTA, OUTB output fall time

See Note 5

200

ns

tr(OUT)

OUTA, OUTB output rise time

See Note 5

200

ns

NOTE 5: Design target only. Not tested in production.

thermal resistance

PARAMETER

TEST CONDITIONS

MIN

MAX

UNIT

RθJ(SYS) Thermal resistance, in system

2 oz. copper traces, JEDEC low K board, 0 LFPM airflow

58.4

°C/W

RθJC

Thermal resistance, junction-to-case

Exposed back-side die mount

4.7

°C/W

PRINCIPLES OF OPERATION

general overview

The THMC45 is a dc 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, bipolar-wound stator. The device is intended primarily for

low-voltage cooling fan applications requiring speed control with a tachometer feedback signal to ensure normal

fan operation. The output drive PWM duty cycle and frequency are dependent on the input signal on the PWM

terminal. The device has an internal Hall sensor amplifier and signal conditioning with drive commutation logic,

a low power sleep-state mode, and locked rotor protection with automatic restart after a locked rotor condition.

The PWM terminal is used to input PWM frequency and duty cycle, to output a tachometer current pulse

feedback signal, and to provide a means for entering sleep and run states. The THMC45 provides a more

effective drive solution to fan RPM control than either external linear voltage regulation or external PWM drive.

The device is offered in an MSOP-8 miniature surface-mount package to meet the critical space constraints of

PCB designs of small low-voltage fans typically found in notebook PCs.

placed as close to this terminal as layout permits.