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參數(shù)資料
| 型號(hào)： | A8905CLB |
| 廠商： | Allegro MicroSystems, Inc. |
| 英文描述： | 3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER WITH BACK-EMF SENSING |
| 中文描述： | 3相無刷直流電動(dòng)機(jī)控制器/驅(qū)動(dòng)器，反電動(dòng)勢(shì)遙感 |
| 文件頁數(shù)： | 6/12頁 |
| 文件大?。?/td> | 163K |
| 代理商： | A8905CLB |
8905
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Power Outputs.
The power outputs of the
A8905CLB are n-channel DMOS transistors with
a total source plus sink r
DS(on)
of typically 1.1
.
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 induc-
tive 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 A8905CLB provides 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:
Sequencer
State
OUT
A
OUT
B
OUT
C
1
2
3
4
5
6
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 (output crossing
through centertap). True back-EMF zero cross-
ings 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.
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 synchronous 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.
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)
VCSTL
VCSTH
VCWD
VCST
CST
t
Dwg. WP-020
FUNCTIONAL DESCRIPTION
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