A8932CLWA 데이터 시트보기 (PDF) - Allegro MicroSystems
부품명
상세내역
제조사
A8932CLWA Datasheet PDF : 8 Pages
| |||
8932-A
VOICE-COIL MOTOR DRIVER
DEVICE DESCRIPTION
Current Amplifier. The A8932CLWA voice-coil motor
driver features a wide transcon-ductance bandwidth and
minimal crossover distortion. The transconductance gain
is user selectable:
A
g= i
m
Rgm
(Equation 1)
where Ai is either 2000 (H GAIN = Low) or 8000 (H GAIN =
High).
The error amplifier’s bandwidth and load compensa-
tion zero are set utilizing external resistor and capacitor
feedback components around the amplifier.
The actuator main loop compensation can be set by
applying a square wave and adjusting R and C for
Z
Z
optimum response.
Current and Voltage Sensing. The load current is
sensed internally. Three auxiliary amplifiers are also
included to allow various control functions to be imple-
mented. The first of these amplifiers provides a voltage
output that is proportional to the load current:
VSENSE =
RS ILOAD
Ai
(Equation 2)
The second and third auxiliary amplifiers may be used
in conjunction with the first to provide a closed-loop
velocity control system for the actuator arm during a
controlled retract for head parking. This is achieved by
determining the back-EMF voltage generated by the voice
coil and feeding back this information to the main actuator
control input. The back-EMF feedback voltage can be
switched in as required by means of the SWITCH logic
input.
The back-EMF voltage represents the velocity of the
actuator. By subtracting the I R voltage component
LOAD LOAD
from the voltage across the load, the back-EMF term can
be isolated and fed back to close a velocity control loop.
The amplifier output voltage V is proportional to the
LOAD
voltage across the load (AVD[VOUTN - VOUTP]). RS is selected
so that VSENSE represents ILOAD while R3 is dependent on
R as shown in the following equations:
LOAD
V = -A ([I R ] + V )
LOAD
VD LOAD LOAD
BEMF
VSENSE = RS ILOAD/AiL
where Ai = 2000 (H GAIN = logic Low)
OUTSW = 0.4 (VBEMF R1/R2)
R3 =
R2 RS
0.4 Ai RLOAD
VBEMF
VIN
=
R2 RVgm
0.4 Rgm R1
RKKA
BW = 0.4
1BTi
2π RVGM R2 J
where J is the moment of inertia, KB is the back-EMF
motor constant, and K is the torque constant.
T
Velocity loop compensation =
LLOAD/RLOAD = R1 C1 = R3 C2.
V IN
1/Rgm
+∑
–
A i = 2000 or 8000
Ai
..
Ø
KT /J
1/S
.
Ø
KB
1/R Vgm
0.4 R1 /R2
K1
VBEMF
Dwg. OP-003B
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Share Link: 