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ML4411CS bảng dữ liệu(PDF) 6 Page - Micro Linear Corporation |
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ML4411CS bảng dữ liệu(HTML) 6 Page - Micro Linear Corporation |
6 / 14 page 6 ML4411/ML4411A Minute. The minimum VCO gain derived from the specification table (using the minimum Fvco at VVCO = 6V) is: K C VCO MIN VCO () . = × − 242 10 6 Assuming that the VVCO(MAX) = 9.5V, then C F VCO MAX = ×× − 95 242 10 6 .. or C POLES RPM F VCO = × 460 µ 02 468 10 12 3000 2500 2000 1500 1000 500 0 0.01 µF 0.02 µF VVCO (VOLTS) Figure 3. VCO Output Frequency vs. VVCO (Pin 20) Figure 4 shows the transfer function of the Phase Lock Loop with the phase detector formed from the sampled phase through the Gm amplifier with the loop filtered formed by R, C1, and C2. The impedance of the loop filter is Zs Cs s s RC LEAD LAG () () () = + + 1 1 ω ω R C1 C2 VCO – + ZRC RC FOUT KVCO(HZ/V) Gm = 1.25 x 10–4 SAMPLED PHASE Figure 4. Back EMF Phase Lock Loop Components Where the lead and lag frequencies are set by: ωLEAD RC = 1 2 ωLAG CC RC C = + 12 12 START-UP SEQUENCING When the motor is initially at rest, it is generating no back-EMF. Because a back-EMF signal is required for closed loop commutation, the motor must be started “open-loop” until a velocity sufficient to generate some back-EMF is attained (around 100 RPM). The following steps are a typical procedure for starting a motor which is at rest. Step 1: The IC is held in reset (state R) with full power applied to the windings (see figure 6). This aligns the rotor to a position which is 30° (electrical) before the center of the first commutation state. Step 2: Reset is released, and a fixed current is input to pin 21 and appears as a current on pin 20, and will ramp the VCO input voltage, accelerating the motor at a fixed rate. Step 3: When the motor speed reaches about 100 RPM, the back EMF loop can be closed by pulling pin 18 high. RESET/ ALIGN P1, P3, N2 ON OPEN-LOOP (STEPPING) CLOSED LOOP 0 RESET ENABLE E/A Figure 6. Typical Start-up Sequence. Using this technique, some reverse rotation is possible. The maximum amount of reverse rotation is 360/N, where N is the number of poles. For an 8 pole motor, 45° reverse rotation is possible. For quick recovery following a momentary power failure, the following steps can be taken: PIN PIN PIN ILIMIT STEP 16 18 21 ICMD 1 0 0 FIXED IMAX 2 1 0 FIXED IMAX 3110 IMAX Table 2. Start-up Sequence. |
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