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ML4411CS Datasheet(PDF) 5 Page - Micro Linear Corporation |
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ML4411CS Datasheet(HTML) 5 Page - Micro Linear Corporation |
5 / 14 page 5 ML4411/ML4411A maximum voltage at any PH input does not exceed VCC. NEUTRAL 0 60 120 180 240 0 300 Figure 2. Typical motor phase waveform with Back-EMF superimposed (Ideal Commutation) VCO AND PHASE DETECTOR CALCULATIONS The VCO should be set so that at the maximum frequency of operation (the running speed of the motor) the VCO control voltage will be no higher than VCCMIN – 1V. The VCO maximum frequency will be: F POLES RPM MAX =× × 005 . where POLES is the number of poles on the motor and RPM is the maximum motor speed in Revolutions Per FUNCTIONAL DESCRIPTION The ML4411 provides closed-loop commutation for 3-phase brushless motors. To accomplish this task, a VCO, integrating Back-EMF Sampling error amplifier and sequencer form a phase-locked loop, locking the VCO to the back-EMF of the motor. The IC also contains circuitry to control motor current with either linear or constant off- time PWM modes. Braking and power fail detection functions are also provided on chip. The ML4411 is designed to drive external power transistors (N-channel sinking transistors and PNP sourcing transistors) directly. Start-up sequencing and motor speed control are accomplished by a microcontroller. Speed sensing is accomplished by monitoring the output of the VCO, which will be a signal which is phased-locked to the commutation frequency of the motor. BACK-EMF SENSING AND COMMUTATOR The ML4411 contains a patented back-EMF sensing circuit which samples the phase which is not energized (Shaded area in figure 2) to determine whether to increase or decrease the commutator (VCO) frequency. A late commutation causes the error amplifier to charge the filter (RC) on pin 20, increasing the VCO input while early commutation causes pin 20 discharge. Analog speed control loops can use pin 20 as a speed feedback voltage. The input impedance of the three PH inputs is about 8Ký to GND. When operating with a higher voltage motor, the PH inputs should be divided down in voltage so that the FIGURE 1. BACK EMKF sensing block diagram NEUTRAL SIMULATOR ΦA + ΦB + ΦC 6 ΦA ΦB ΦC MULTIPLEXER R C1 C2 VCO COMMUTATION LOGIC SIGN CHANGER b a – + I(PIN 21) + LOOP FILTER IRC = Va – Vb 8K RC VCO /TACH OUT + – DIS PWR 8K 8K ROTATION SENSE |
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