a8902 Allegro MicroSystems, Inc., a8902 Datasheet - Page 10

• Manufacturer Part Number: a8902
• Description: 3-phase Brushless Dc Motor Controller/driver With Back-emf Sensing
• Manufacturer: Allegro MicroSystems, Inc.

Braking. A dynamic braking feature of the A8902CLBA shorts the
three motor windings to ground. This is accomplished by turning the
three source drivers OFF and the three sink drivers ON. Activation of
the brake can be implemented through the BRAKE input or through
the D2 bit in the serial port. The supply voltage for the brake circuitry
is the C
power failure. Power-down braking with delay can be implemented by
using an external RC and other components to control the brake
terminal, as shown. Brake delay can be set using the equation below
to ensure that voice-coil head retract occurs before the spindle motor
10
FAULT
8902–A
3-PHASE BRUSHLESS DC
MOTOR CONTROLLER/DRIVER
RES
voltage, allowing the brake function to remain active after
C B
R
B
FAULT
V RET
BRAKE
BYPASS
R B
V
FAULT
C B
C
0.22 F
RES
– V
C D2
C
V
C
ST
BB
WD
D
10
12
8
9
11
1
2
3
4
5
6
7
9
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 [phone]
t
V
BRK
BB
CHARGE
BOOST
PUMP
ACTIVATED
COMMUTATION
BRAKE
DELAY
Dwg. OP-004
MUX
FLL
V BRK
V
DD
24
21
17
23
22
20
19
18
16
13
15
14
brake is activated. Once the brake is acti-
vated, due to the inherent capacitive input,
the three sink drivers will remain active until
the device is reset.
t
simulates the centertap voltage of the motor.
To obtain reliable start-up performance from
motor to motor, the motor centertap should be
connected to this terminal.
cations information regarding the selection of
external component values is available from
the factory for external component selection,
frequency-locked loop speed control, and
commutation delay capacitor selection.
BRK
BYPASS
CHIP SELECT
RESET
DATA IN
CLOCK
SECTOR
DATA
+5 V
Centertap. The A8902CLBA internally
External Component Selection. Appli-
= R
B
C
DATA OUT
OSC (REF)
C F2
B
C D1
R F1
Dwg. EP-036C
1 – l
C F1
n
V
FAULT -
V
BRK
V
D