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8905 Schematic ( PDF Datasheet ) - Allegro MicroSystems

Teilenummer 8905
Beschreibung 3-PHASE BRUSHLESS DC MOTOR CONTROLLER/DRIVER WITH BACK-EMF SENSING
Hersteller Allegro MicroSystems
Logo Allegro MicroSystems Logo 




Gesamt 12 Seiten
8905 Datasheet, Funktion
8905
3-PHASE BRUSHLESS DC
8905MOTOR CONTROLLER/DRIVER
3-PHASE BRUSHLESS DC MOTOR
CONTROLLER/DRIVER WITH BACK-EMF SENSING
The A8905CLB isw a three-phase brushless dc motor controller/
driver for use with CD-ROM or DVD drives. The three half-bridge
LOAD
SUPPLY
1
V BB
COMMUTATION
DELAY
24 C D1
outputs are low on-resistance n-channel DMOS devices capable of
driving up to 1.25 A. The A8905CLB provides complete, reliable,
C D2 2
23 DATA IN
self-contained back-EMF sensing motor startup and running algorithms.
C WD 3
22 CLOCK
A programmable digital frequency-locked loop speed control circuit
together with the linear current control circuitry provides precise motor
CST 4
OUTA 5
GROUND 6
TGROUND 7
COUTB 8
UOUTC 99
D YCENTERTAP 10
LBRAKE 11
O NCRES 12
21 CHIP SELECT
20 RESET
19 GROUND
18 GROUND
MUX
17 DATA OUT
BOOST
CHARGE
PUMP
FLL 16 OSCILLATOR
VDD 15
LOGIC
SUPPLY
14 INDEX
13 FILTER
R ODwg. PP-040-1
P EABSOLUTE MAXIMUM RATINGS
at TA = +25°C
D CLoad Supply Voltage, VBB . . . . . . 14 V
E NOutput Current, IOUT . . . . . . . . ±1.25 A
Logic Supply Voltage, VDD . . . . 6.0 V
U ELogic Input Voltage Range,
INVIN . . . . . . . -0.3 V to VDD + 0.3 V
RPackage Power Dissipation,
T EPD . . . . . . . . . . . . . . . . See Graph
Operating Temperature Range,
N FTA . . . . . . . . . . . . . . 0°C to +70°C
O EJunction Temperature, TJ . . . +150°C†
Storage Temperature Range,
C RTS . . . . . . . . . . . . -55°C to +150°C
† Fault conditions that produce excessive
junction temperature will activate device thermal
IS Rshutdown circuitry. These conditions can be
tolerated, but should be avoided.
D OOutput current rating may be restricted to a value
Fdetermined by system concerns and factors.
speed regulation.
A serial port allows the user to program various features and modes
of operation, such as the speed control parameters, startup current limit,
sleep mode, diagnostic modes, and others.
APPLICATIONS
s CD-ROMs
s DVDs
FEATURES
s DMOS Outputs
s Low rDS(on)
s Startup Commutation Circuitry
s Back-EMF Commutation Circuitry
s Serial Port Interface
s Frequency-Locked Loop Speed Control
s Tachometer Signal Input
s Programmable Start-Up Current
s Diagnostics Mode
s Sleep Mode
s Linear Current Control
s Internal Current Sensing
s Dynamic Braking Through Serial Port
s Power-Down Dynamic Braking
s System Diagnostics Data Out
s Data Out Ported in Real Time
s Internal Thermal Shutdown Circuitry
These include: system duty cycle and timing,
ambient temperature, and use of any heatsinking
and/or forced cooling. For reliable operation, the
specified maximum junction temperature should
not be exceeded.
Always order by complete part number, e.g., A8905CLB .






8905 Datasheet, Funktion
8905
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER
FUNCTIONAL DESCRIPTION
Power Outputs. The power outputs of the
A8905CLB are n-channel DMOS transistors with
a total source plus sink rDS(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
1
2
3
4
5
6
OUTA
High
Z
Low
Low
Z
High
OUTB
Low
Low
Z
High
High
Z
OUTC
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.
V OUTA
V OUTB
V OUTC
SOURCE ON
V CTAP
BACK-EMF VOLTAGE
SINK ON
FCOM TOGGLES AT
BACK-EMF ZERO CROSSING
FCOM
Dwg. WP-016-1
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 CST.
VCST
VCSTH
VCWD
VCSTL
t CST
Dwg. WP-020
where
tCST =
4(VCSTH - VCSTL) x CST
IST(charge) + IST(discharge)
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 CST at each commutation, which prevents CST from reaching its
upper threshold and thus completing a cycle and commutating.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

6 Page









8905 pdf, datenblatt
8905
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER
Allegro MicroSystems, Inc. reserves the right to make, from time
to time, such departures from the detail specifications as may be
required to permit improvements in the design of its products.
The information included herein is believed to be accurate and
reliable. However, Allegro MicroSystems, Inc. assumes no
responsibility for its use; nor for any infringements of patents or
other rights of third parties which may result from its use.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000

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