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Moteur de recherche de fiches techniques de composants électroniques |
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Moteur de recherche de fiches techniques de composants électroniques |
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ML4435CS Fiches technique(PDF) 9 Page - Micro Linear Corporation |
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ML4435CS Fiches technique(HTML) 9 Page - Micro Linear Corporation |
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9 / 14 page  May, 2000 PRELIMINARY DATASHEET 9 PRELIMINARY ML4435 FUNCTIONAL DESCRIPTION MOTOR START-UP When power is first applied to the ML4435, the motor is at rest and thus, the back EMF is equal to zero. The motor needs to be rotating for the Back EMF sampler to lock onto the rotor position and commutate the motor. The ML4435 uses a minimum VCO frequency to begin commutating the motor. This low frequency commutation is set by the 0.2V clamp on RVCO, this provides a commutation frequency at 1/30th of the maximum frequency. RUN MODE After the Back EMF sensing PLL has locked on to the motor’s position, the motor is running in closed loop con- trol. At this point, the speed control loop should force the motor speed to the speed that corresponds to the SPEED SET voltage. PWM SPEED CONTROL Speed control is accomplished by setting a speed com- mand at SPEED SET (pin 5) with an input voltage from 0.2 to 6V. The accuracy of the speed command is determined by the external components RVCO and CVCO. There are a number of methods to control the speed command on the ML4435. One method is to use a potentiometer from RT to ground with the wiper going to SPEED SET. If SPEED SET is controlled from a microcontroller, a DAC that uses RT as its input reference can be used. The RT voltage must be buffered connecting it to external circuits. The speed command is compared with the sensed speed from SPEED FB minus 0.7V (pin 18) through a transconductance error amplifier. The output of the speed error amplifier is SPEED COMP (pin 3). SPEED COMP is clamped between 8.2V and 2.2V. A signal of 8.2V corresponds to full PWM duty cycle and 2.2V corresponds to 0% duty cycle. Speed loop compensation components are placed on this pin as shown in Figure 11. The speed loop compensation components are calculated as follows: C NxKexVMOTOR R C J RI freq SC VCO VCO 2 144 2 2 = ×× × ×× × × . π Rsc freq Csc = ×× × 10 22 π Csc1 = 10 x Csc2 Where freq is the speed loop bandwidth in Hz. Figure 11. PWM Oscillator Circuit The voltage on SPEED COMP (pin 3) is compared with a triangle wave oscillator to create a PWM duty cycle. The PWM oscillator creates a triangle wave function from 3V to 7V as shown in Figure 11. The frequency of the triangle wave oscillator is set by a resistor to ground on RT (pin 6). RT can be selected from the graph in Figure 12. The PWM duty cycle from the speed control loop is gated the pulse-by-pulse current limit that controls the LA, LB, and LC output drivers. Figure 12. RT vs PWM Frequency SPEED COMP SPEED SET V 3V 5 SPEED FB + – PWM COMPARATOR TRIAN LE WAVE COMPARATOR SPEED ERROR AMP LEVEL SHIFT 0. V + – 2.2 + 0. V CSE .2 - 0. V – + 3 PWM FRE UENCY kHz 000 000 00 0 |
Numéro de pièce similaire - ML4435CS |
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Description similaire - ML4435CS |
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