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参数资料
| 型号： | 8906 |
| 厂商： | Allegro MicroSystems, Inc. |
| 英文描述： | BIDIRECTIONAL 3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER WITH BACK-EMF SENSING |
| 中文描述： | 双向三相无刷直流电机控制器/返回驱动程序，电磁场遥感 |
| 文件页数： | 6/12页 |
| 文件大小： | 159K |
| 代理商： | 8906 |
8906
BIDIRECTIONAL
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
(output crossing through centertap). 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. Back-EMF zero crossings are indicated by FCOM, an internal
signal that toggles at every zero crossing. FCOM is available at the
DATA OUT terminal via the programmable data out multiplexer.
Direction Control.
Serial port bit D2 controls the direction of
rotation (see sequencer state table). The motor should be at a com-
plete stop before beginning a startup sequence that reverses the
direction of rotation.
Startup Oscillator.
If the motor does not move at the initial startup
state, then it is in a null-torque position. In this case, the outputs are
commutated automatically by the startup oscillator after a period set by
the external capacitor at C
ST
where
t
CST
=
In the next state, the motor will move, back EMF will be detected,
and the motor will accelerate synchronously. Once normal synchro-
nous back-EMF commutation occurs, the startup oscillator is defeated
by pulses of pulldown current at C
ST
at each commutation, which
prevents C
ST
from reaching its upper threshold and thus completing a
cycle and commutating.
Power Outputs.
The power outputs of
the A8906CLB are n-channel DMOS transis-
tors with a total source plus sink r
DS(on)
of
typically 1
. Internal charge pump boost
circuitry provides voltage above supply for
driving the high-side DMOS gates. Intrinsic
ground clamp and flyback diodes provide
protection when switching inductive loads and
may be used to rectify motor back-EMF in
power-down conditions. An external Schottky
power diode or pass FET is required in series
with the load supply to allow motor back-EMF
rectification in power down conditions.
Back-EMF Sensing Motor Startup and
Running Algorithm.
The A8906CLB pro-
vides a complete self-contained back-EMF
sensing startup and running commutation
scheme. The three half-bridge outputs are
controlled by a state machine. There are six
possible combinations. In each state, one
output is high (sourcing current), one low
(sinking current), and one is OFF (high
impedance or
‘
Z
’
). Motor back EMF is sensed
at the OFF output. The truth table for the
output drivers sequencing is:
Direction
Control
OUT
A
OUT
B
OUT
C
High
Z
Low
Low
Z
High
Low
Low
Z
High
High
Z
Z
High
High
Z
Low
Low
At startup, the outputs are enabled in one
of the sequencer states shown. The back
EMF is examined at the OFF output by
comparing the output voltage to the motor
centertap voltage at CENTERTAP. The
motor will then either step forward, step
backward, or remain stationary (if in a null-
torque position). If the motor moves, the
back-EMF detection circuit waits for the
correct polarity back-EMF zero crossing
FUNCTIONAL DESCRIPTION
Dwg. WP-016-1
FCOM
FCOM TOGGLES AT
BACK-EMF ZERO CROSSING
SOURCE ON
SINK ON
BACK-EMF VOLTAGE
VOUTA
VOUTB
VOUTC
VCTAP
4(V
CSTH
- V
CSTL
) x C
ST
I
ST(charge)
+ I
ST(discharge)
D
D
相关PDF资料 |
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|---|---|
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| 8910 | T-1 Subminiature Lamps |
| 8920 | DUAL SCHOTTKY DIODE |
| 8925 | 3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER WITH LINEAR CURRENT CONTROL AND POWER DMOS OUTPUTS |
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