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ML4428 Folha de dados(PDF) 6 Page - Micro Linear Corporation |
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ML4428 Folha de dados(HTML) 6 Page - Micro Linear Corporation |
6 / 16 page 6 ML4428 FUNCTIONAL DESCRIPTION The ML4428 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 contains circuitry to control motor speed in PWM mode. Braking and power fail detection functions are also provided on the chip. The ML4428 is designed to drive external power transistors (N-channel sinking transistors and P-channel sourcing transistors) directly. The ML4428 limits the motor current with a constant off- time PWM controlled current. The velocity loop is controlled with an on-board amplifier. An accurate, jitter- free VCO output is provided equal to the commutation frequency of the motor. The ML4428 switches the gates of external N-channel power MOSFETs to regulate the motor current and directly drives the P-channel MOSFETs for 12V motors. The ML4428 ensures that there is no shoot through in any state of power drive to the FETs. Higher voltage motors can be driven using buffer transistors or standard “high side” drivers. Speed sensing is accomplished by monitoring the output of the VCO, which will be a signal which is phase-locked to the commutation frequency of the motor. BACK-EMF SENSING AND COMMUTATOR The ML4428 contains a patented back-EMF sensing circuit (Figure 1) 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 RCVCO, increasing the VCO input while early commutation causes RCVCO to discharge. The analog speed control loop uses RCVCO as a speed feedback voltage. The input impedance of the three PH inputs is about 8.7ký to GND. When operating with a higher voltage motor, the PH inputs should be divided down in voltage with series resistors so that the 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). Figure 1. Back-EMF Sensing Block Diagram NEUTRAL SIMULATOR ΦA + ΦB + ΦC 9 PHI1 PHI2 PHI3 MULTIPLEXER R C1 C2 VCO COMMUTATION LOGIC SIGN CHANGER b a – + LOOP FILTER I(RC) = Va – Vb 4.35K RCVCO 2.9K 5.8K VCO 22 23 24 |
Nº de peça semelhante - ML4428 |
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Descrição semelhante - ML4428 |
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