THMC40_11 Datasheet, PDF (13/19 Pages) Texas Instruments – VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS

THMC40, THMC41
VARIABLE SPEED 12-VDC BRUSHLESS FAN MOTOR DRIVERS
SLIS097 – MARCH 2000
open-drain tachometer output (TACH)—THMC40 Only
The THMC40 TACH output is an open-drain output activated by the Hall sensor comparator output (see Figure
9). When the Hall sensor comparator output is high, the TACH output floats high. When the Hall sensor amplifier
output is low, the TACH output is pulled low. The resulting output signal has two pulses per revolution on a
four-pole motor.
The TACH output can be used to monitor and measure actual fan speed. This output can also be used as part
of a closed-loop speed control system.
NOTE:
It is recommended that the fan manufacturer not place a pullup resistor for this terminal on the fan
circuit board. Leaving the output as open-drain allows the end user to pull up this terminal with an
external resistor to the supply voltage of their choice (that is, 3.3 V or 5 V).
open-drain locked rotor detection output—THMC41 only
The THMC41 RD output is an open-drain output pulled low during normal fan operation and allowed to float
during a locked rotor condition (see Figure 9). This signal can be used to alert the system of a locked rotor
condition.
The RD output can also be used as a fan present or fan OK signal by using a general-purpose input terminal
on a PC Super I/O chip to detect the logic state of this terminal. When this input is high, the signal indicates that
the fan has been disconnected or is in a locked rotor condition.
NOTE:
It is recommended that the fan manufacturer not place a pullup resistor for this terminal on the fan
circuit board. Leaving the output as open-drain allows the end user to pull up this terminal with an
external resistor to the supply voltage of their choice (that is, 3.3V or 5V).
supply voltage input (V_PWR)
The V_PWR terminal serves as the voltage supply input to the THMC40 and THMC41. A 0.1-µF bypass capacitor
should be placed as close to this terminal as the layout permits. Additional bulk capacitance of 2.2 µF to 10 µF
on this terminal is highly recommended to reduce current spikes on the supply line during motor commutation,
thus reducing radiated emissions from the fan. See Application Information for further details.
• POST OFFICE BOX 655303 DALLAS, TEXAS 75265
13