A8980 Ver la hoja de datos (PDF) - Allegro MicroSystems
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A8980 Datasheet PDF : 8 Pages
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8980
SUPERSERVO™
SPINDLE & VOICE-COIL
ACTUATION MANAGER/DRIVER
FUNCTIONAL DESCRIPTION
ACTUATOR
Servo-Demand DAC. A 12-bit DAC
is provided to bridge the DSP “soft” domain
to the analog hardware domain. The term
“demand” refers to the distinction between
the newly requested voice-coil current and
the prior current being supplied. The DAC,
operating in straight binary format, spans the
full dynamic range between a large signal
velocity and a precision position mode. The
DAC output is updated synchronously with
the notch functions to avoid the creation of
aliasing products.
Low-Pass Filter. This double, non-
intrinsic complex-pole low-pass filter is
provided to attenuate undesirable, out-of-
band information. The input of this discrete
time filter is sampled synchronously with the
12-bit DAC and notch function in order to
avoid aliasing products.
Notch Filter. This notch filter has a programmable center
frequency and programmable notch depth to provide truly independent
control of notch damping. Enough range and granularity are provided
to allow versatile and accurate out-of-band attenuation of undesirable
energy sources.
Actuator Transconductance Amplifier. The final trans-
conductance function of the voice-coil actuation signal path is
achieved by monitoring the load current and generating an error
voltage to drive a local gm amplifier control loop. The error voltage is
scaled by an external precision resistor (Rgm(act)). This resistor does
not carry load current and is intended only for accurate determination
of the transconductance. The function is:
gm(act)
=
5800
Rgm(act)
A/V
and IOUT = VSERVO • gm(ACT).
Actuator Power Outputs. The voice-coil output driver is a
full-bridge power driver operating in a class-B mode. The power
output devices are enhancement-mode MOS transistors. Special
internal circuitry results in nearly zero cross-over distortion when
switching from one source/sink pair to another.
V CC(A)
V BG
TRIP ADJ
V BOOST(L)
VCC(PWR)
VM
V CC(A)
UNDER-VOLTAGE
FAULT
L FLYBACK
DC-TO-DC
CONVERTER
VDC+ VM
VCC(D)
POWER
ON
RESET
POR
OUT
V BOOST(H)
V BOOST(L)
V BOOST(H)
V BOOST(L)
V DC
ADJUST
(FROM SERIAL
INTERFACE)
V BG
RETRACT
VOLTAGE
REFERENCE
V RETRACT
SPINDLE
MOTOR DRIVERS
VOICE-COIL
DRIVER
FILTERED
V VEL
VCC(A)
V BOOST(L)
V BOOST(L)
V CC(A)
V REF
+
V REF
2
V REF
-
V REF
2
TJ
V BG
OVER -
VELOCITY
FAULT
VCC(D)
THERMAL
FAULT
RETRACT
MODE
BANDGAP VBG
REFERENCE
VOLTAGE
REFERENCE
ADJUST
x2
SHUTDOWN /
SLEEP
ADJUST
(FROM SERIAL INTERFACE)
VCC(A)
÷2
V BOOST(H)
V BOOST(L)
V REF(x2)
V REF
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