 |
Electronic Components Datasheet Search |
|
|
Electronic Components Datasheet Search |
|
A8904SLP-T Datasheet(PDF) 9 Page - Allegro MicroSystems |
|
||||||||||||||||||||||||||||||
A8904SLP-T Datasheet(HTML) 9 Page - Allegro MicroSystems |
|
|
9 / 18 page  8904 3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER www.allegromicro.com 9 If the motor moves, the back-EMF detection and direction circuit waits for the correct polarity of back-EMF zero crossing (output crossing through centertap). If the correct polarity of back-EMF is not detected, a watchdog circuit commutates the output until the correct back-EMF is detected. Correct back- EMF sensing is indicated by the FCOM signal, which toggles every time the back-EMF completes a zero crossing (see waveforms below). FCOM is available at the DATA OUT terminal. True back-EMF zero crossings are used by the adaptive commutation delay circuit to advance the state sequencer (commutate) at the proper time to synchronously run the motor. See next section. Adaptive commutation delay. The adaptive commuta- tion delay circuit uses the back-EMF zero-crossing indicator signal (FCOM) to determine an optimal commutation time for efficient synchronous switching of the output drivers. When the FCOM signal changes state, one of the delay capacitors (C D1 or C D2) is discharged at approximately twice the rate of the charging current. When the capacitor reaches the 2.5 V thresh- old, a commutation occurs. During this discharge period, the other delay capacitor is being charged in anticipation of the next FCOM state change. In addition, there is an interruption to the charging, which is set by the blanking duration (see waveform below, V CWD, and next section). This additional charging delay causes the commutation to occur at slightly less than 50% of the FCOM on or off duration, to compensate for delays caused by winding inductance. Functional Description (cont’d) The typical delta voltage change during normal operation in the commutation capacitors (C D1 & CD2), will range between 1.5 V and 2.0 V. The commutation capacitor values can be determined from: C DX = ICD x t / VCD where V CD = 1.5 V, ICD = 20 µA, and t = (60/rpm)/(#motor poles x 3), duration of each state. To avoid the capacitors charging to the supply rail, the value selected should provide adequate margin, taking into account the effects of capacitor tolerance, charging current, etc. Blanking and watchdog timing functions. The blanking and watchdog timing functions are derived from one timing capacitor C WD . During normal commutation, at the beginning of each new sequencer state, a blanking signal is created until the watchdog capacitor C WD is charged to the threshold VTL (see waveforms below). This blanking signal prohibits the back-EMF compara- tors from tripping due to the discharging of inductive energy and voltage settling transients during sequence state transitions. The duration of this blanking signal depends on the size of the C WD capacitor and the programmed charge current, I CWD (via D26- 27). This blanking pulse also interrupts the commutation delay capacitors C D1 and CD2 from charging (see previous section). The ability to select the minimum charge current for C WD is particularly useful during start-up, where the duration of the diode recirculation current is highest. In applications where high motor speeds are experienced, the charge current can be increased so that the blanking period does not encroach signifi- cantly into the period of each sequencer state and does not cause |
Similar Part No. - A8904SLP-T |
|
Similar Description - A8904SLP-T |
|
|
|
Link URL |
| Privacy Policy |
| ALLDATASHEET.COM |
| Does ALLDATASHEET help your business so far? [ DONATE ] |
About Alldatasheet | Advertisement | Datasheet Upload | Contact us | Privacy Policy | Link Exchange | Manufacturer List All Rights Reserved©Alldatasheet.com |
| Russian : Alldatasheetru.com | Korean : Alldatasheet.co.kr | Spanish : Alldatasheet.es | French : Alldatasheet.fr | Italian : Alldatasheetit.com Portuguese : Alldatasheetpt.com | Polish : Alldatasheet.pl | Vietnamese : Alldatasheet.vn Indian : Alldatasheet.in | Mexican : Alldatasheet.com.mx | British : Alldatasheet.co.uk | New Zealand : Alldatasheet.co.nz |
|
Family Site : ic2ic.com |
icmetro.com |
English ▼
English
Chinese
German
Japanese
Russian
Korean
Spanish
French
Italian
Portuguese
Polish
Vietnamese
Indian
Mexican
British
New Zealand
