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參數(shù)資料
| 型號： | 8902-A |
| 英文描述： | 3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER WITH BACK-EMF SENSING |
| 中文描述： | 3相無刷直流電動機(jī)控制器/驅(qū)動器，反電動勢遙感 |
| 文件頁數(shù)： | 6/12頁 |
| 文件大小： | 156K |
| 代理商： | 8902-A |
8902–A
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
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 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 indi-
cated 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 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.
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)
Power Outputs.
The power outputs of
the A8902CLBA are n-channel DMOS
transistors 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 A8902CLBA
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
FUNCTIONAL DESCRIPTION
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