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TDA5341 датащи(PDF) 11 Page - NXP Semiconductors |
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TDA5341 датащи(HTML) 11 Page - NXP Semiconductors |
11 / 28 page 1997 Jul 10 11 Philips Semiconductors Product specification Brushless DC motor and VCM drive circuit with speed control TDA5341 The Timing Capacitor (CAPTI) Capacitor CAPTI is used for timing the successive steps within one commutation period; these steps include some internal delays. The most important function is the watchdog time in which the motor EMF has to recover from a negative diode pulse back to a positive EMF voltage (or vice-versa). A watchdog timer is a guarding function that only becomes active when the expected event does not occur within a predetermined time. The EMF usually recovers within a short time if the motor is running normally (<<ms). However, if the motor is motionless or rotating in the reverse direction, then the time can be longer (>>ms). A watchdog time must be chosen so that it is long enough for a motor without EMF (still) and eddy currents that may stretch the voltage in a motor winding. However, it must be short enough to detect reverse rotation. If the watchdog time is made too long, then the motor may run in the wrong direction (with little torque). The capacitor is charged, with a current of 60 µA, from 0.03 to 0.3 V. Above this level it is charged, with a current of 5 µA, up to 2.2 V only if the selected motor EMF remains in the wrong polarity (watchdog function). At the end, or, if the motor voltage becomes positive, the capacitor is discharged with a current of 30 µA. The watchdog time is the time taken to charge the capacitor, with a current of 5 µA, from 0.3 to 2.2 V. The value of CAPTI is given by: Where: C is in nF and t is in ms. Example: If, after switching off, the voltage from a motor winding is reduced, in 3.5 ms, to within 10 mV (the offset of the EMF comparator), then the value of the required timing capacitor is given by: C = 2.63 × 3.5 = 9.2 (choose 10 nF) Typical voltage waveforms are illustrated by Fig.4. C5 10 6 – × t m 1.9 -------- 2.63t m = × = Fig.4 Typical CAPTI and VMOT1 voltage waveforms in normal running mode. If the chosen value of CAPTI is too small, then oscillations can occur in certain positions of a blocked rotor. If the chosen value is too large, then it is possible that the motor may run in the reverse direction (synchronously with little torque). handbook, full pagewidth MGE821 voltage on CAPTI VMOT1 |
Аналогичный номер детали - TDA5341 |
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Аналогичное описание - TDA5341 |
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