THMC40_11 Datasheet, PDF (8/19 Pages) Texas Instruments – VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS

THMC40, THMC41
VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS
SLIS097 – MARCH 2000
high-side PWM output driver (V_OUT)
Referring to Figure 3, V_OUT is a drive output to provide PWM controlled power to the common node of the motor
phase windings using an internally generated PWM signal. The PWM duty cycle controls the effective drive
power to the motor, and thus motor speed. The high-side V_OUT DMOS output transistor has a typical R_DS(ON)
of 400 mΩ at 25°C and a 1-A continuous current.
CP
COSC
2200 pF
Triangle Wave
Generator
0.5 V to 2.3 V
VPWM
PUC
COMP
PWM
Charge Pump,
HS Gate Drive,
Synchronous
Rectification,
and
Global Thermal
Shutdown
High-Side
Driver
Synchronous
Low-Side
Switch
0.1 µF
VPWR
VOUT
Figure 3. High-Side PWM Drive
The frequency of the PWM drive (typically 23 kHz) is such that the L/R time constant of the motor phase winding
filters the current. Referring to Figure 4, during the on-time (t_ON) of a PWM period, V_OUT is driven high forcing
voltage across a phase winding and increasing the current. During t_OFF, PWM off-time, the V_OUT high-side
DMOS is switched off, the phase winding inductive energy is recirculated, and the current decreases. To
minimize the voltage drop and the resulting energy loss during recirculation, a low-side DMOS synchronous
switch is provided, as shown in Figure 3. This low-side DMOS device has a 2-A minimum current limit to prevent
device failures should a solder bridge occur between the adjacent V_PWR and V_OUT terminals.
IMOTOR
PWM
IDRIVE
IRECIRCULATE
tPWM
tON
tOFF
Time
Figure 4. Motor Current Waveform
The V_OUT circuit is protected by the global thermal shutdown of the THMC40 and THMC41 by turning off both
the high-side and low-side DMOS drivers when an over-temperature condition is detected. V_OUT is also held
off when the charge-pump voltage (V_CP) is lower than its undervoltage lock-out threshold, V_CP(UVLO).
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