鈥?/div>
3
4
5
LDC
V
BH
BRAKE
FCOM
OUT
B
V
BL
6
GND
GND
7
22
GND
8
21
GND
9
20
R
SENSE
LOAD
SCLK
10
19
18
17
16
15
BKDELAY
ERRCAP
OUTA
11
DATA
12
The A8909CLB is a three-phase brushless, back-EMF sensing,
spindle-motor driver that integrates analog bipolar, analog and digital
CMOS control functions, and DMOS power outputs on a single mono-
lithic chip. It provides complete back-EMF sensing, commutation
control, and drive of a spindle motor, and provides for an orderly spin-
down in the event of supply-voltage removal. Energy for retracting the
heads is regenerated from the spinning motor, while a controlled delay
allows for a full retract before dynamic braking. The pulse-width
modulation system and power DMOS outputs provide control of high
currents with minimum power dissipation in the chip, and minimal
average power supply currrent.
T
C
The internal sensorless commutation algorithm is based on earlier
Allegro back-EMF sensing spindle-motor driver products that have
proven capability. This system features digital adaptive commutation
delay, programmable digital commutation timers, and minimal micro
overhead during startup. This results in enhanced resynchronization
during a power fault followed by a restart.
A serial peripheral interface provides control of programmable
features and mode switches. An onboard dc-to-dc converter provides
regulated boost voltage for both the high-side and sink-side gate-drive
circuits. This provides for optimal r
DS(on)
of sources and sinks, regard-
less of motor supply voltage (5 V or 12 V).
The A8909CLB is supplied in a 28-lead low-profile SOIC batwing
power package for surface-mount applications.
13
VICMD
VM
AMUX
14
Dwg. PP-063
FEATURES
s
3 Half-Bridge DMOS Outputs with Low ON Resistance
s
5 V Logic Supply, 5 V or 12 V Motor Supply
s
Back-EMF Sensing and Commutation Algorithm with
Digital Programmable Timing Functions
s
Adaptive Adjustable Digital Commutation Delay
s
DC-to-DC Boost Voltage Generator for Source and Sink Gate Drive
s
PWM Current-Control Loop with Sink-Side Chopping
s
Transconductance Error Amp. with External Compensation for
Average Supply Current Control Loop
s
PWM Oscillator with External Frequency-Setting Components
s
Current-Sense Amplifier
s
Power-Down Brake with Delay Set by External RC
s
Analog/Digital Multiplexer for Diagnostics and Testing
s
Thermal Monitor Voltage Available on Multiplexer
A
TM
MicroSystems, Inc.
ALLEGRO
1
2
