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THMC45 Datasheet(PDF) 8 Page - Texas Instruments |
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THMC45 Datasheet(HTML) 8 Page - Texas Instruments |
8 / 15 page THMC45 5V AND 3.3V DC BRUSHLESS FAN MOTOR DRIVER WITH SINGLE WIRE CONTROL SLIS101A − MAY 2001 8 POST OFFICE BOX 655303 • DALLAS, TEXAS 75265 PRINCIPLES OF OPERATION PWM input (PWM) The PWM input provides several functions: D Input for controlling H-bridge PWM drive frequency and duty cycle D Output for a tachometer current sink pulse on the first rising edge of the PWM input signal after a commutation D Initiating a low-current sleep state when the voltage maintained a logic low level for 2 ms (typical) or longer, and allowing the THMC45 to return to a normal run state on the next rising edge of the PWM input signal The THMC45 requires a TTL level PWM input signal from another device, such as a Super I/O device. This signal, along with the Hall sensor input, is used to PWM the OUTA and OUTB outputs according to truth table, Table 1. It is recommended that the frequency of the PWM input signal be between 18 kHz and 60 kHz. A PWM frequency of 18 kHz or higher, being above the audible range, ensures quiet fan operation. Frequencies above 18 kHz also promote efficient fan speed control by keeping the PWM period below the electrical L/R time constant of the motor. This allows continuous current in the fan windings (see Figure 3). Keeping the PWM frequency below 60 kHz minimizes switching losses. Switching losses, typically observed at higher frequencies, decreases overall efficiency. The speed of the cooling fan can be varied by adjusting the duty cycle of the PWM input signal. The higher the duty cycle of the PWM input signal, the higher the current in the fan windings, and thus results in faster fan speed. I(MOTOR) PWM I(DRIVE) PWM Period I(RECIRCULATE) tOFF tON Figure 3. Motor Current Waveform |
Similar Part No. - THMC45_13 |
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Similar Description - THMC45_13 |
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