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TDF5242T 数据表(PDF) 6 Page - NXP Semiconductors |
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TDF5242T 数据表(HTML) 6 Page - NXP Semiconductors |
6 / 20 page 1997 Sep 12 6 Philips Semiconductors Preliminary specification Brushless DC motor drive circuit TDF5242T START CAPACITOR (CAP-ST) This capacitor determines the frequency of the start oscillator. It is charged and discharged, with a current of 2 µA, from 0.05 to 2.2 V and back to 0.05 V. The time to complete one cycle is: (1) The start oscillator is reset by a commutation pulse and is only active when the system is in the start-up mode. A pulse from the start oscillator will cause the outputs to change to the next state. If the movement of the motor generates enough EMF, the TDF5242T will run the motor. If the amount of EMF generated is insufficient, then the motor will move one step only and will oscillate in its new position. The amplitude of the oscillation must decrease sufficiently before the arrival of the next start pulse, to prevent the pulse arriving during the wrong phase of the oscillation. The start capacitor should be chosen to meet this requirement. The oscillation frequency of the motor is given by: where: Kt = torque constant (Nm/A) I = current (A) p = number of magnetic pole-pairs J = inertia J (kg.m2). t start 2.15 C × () s (with C in µF ) = f osc 1 2 π K t I × p × J ----------------------- ----------------------------------- = Example: J = 72 × 10−6 kg.m2, K=25 × 10−3 Nm/A,p=6 and I = 0.5 A; this gives fosc = 5 Hz. If the damping is high, a start frequency of 2 Hz can be chosen or t = 500 ms, thus, according to equation (1): C = 0.5/2.15 = 0.23 µF (choose 220 nF). ADAPTIVE COMMUTATION DELAY (CAP-CD AND CAP-DC) In this circuit the capacitor CAP-CD is charged during one commutation period, with an interruption of the charging current during the diode pulse. During the next commutation period the capacitor is discharged at twice the charging current. The charging current is 8.1 µA and the discharging current 16.2 µA; the voltage range is from 0.9 to 2.2 V. The voltage must stay within this range at the lowest commutation frequency of interest, fC1: (C in nF) If the commutation frequency is lower, a constant commutation delay after the zero-crossing is generated by the discharge from 2.2 down to 0.9 V at 16.2 µA; maximum delay = (0.076 × C) ms (with C in nF) Example: nominal commutation frequency = 900 Hz and the lowest usable frequency = 400 Hz; so: (choose 18 nF) The other capacitor, CAP-DC, is used to repeat the same delay by charging and discharging with 15.5 µA. The same value can be chosen as for CAP-CD. Figure 3 illustrates typical voltage waveforms. C 8.1 10 6 – × f 1.3 × -------------------------- 6231 f C1 ------------- == CAP-CD 6231 400 ------------- 15.6 == handbook, full pagewidth t MGG993 Vmax = VIH VIL voltage on CAP-CD voltage on CAP-DC COM COM(1) ZCR ZCR(2) ZCR ZCR ZCR ZCR COM COM COM COM Fig.3 CAP-CD and CAP-DC typical voltage waveforms in normal running mode. (1) COM = commutation. (2) ZCR = zero-crossing. |
类似零件编号 - TDF5242T |
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类似说明 - TDF5242T |
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