A8980: SuperServo Spindle and Voice-Coil Actuation Manager/Driver

8980
Data Sheet
26310
8980
SUPERSERVO™
SPINDLE & VOICE-COIL
ACTUATION MANAGER/DRIVER
TM
SUPERSERVO SPINDLE & VOICE-COIL
ACTUATION MANAGER/DRIVER
MULTIPLEXER
C TAP
The A8980CJT provides complete drive, management, and control
of the voice-coil and spindle motor power actuation subsystems used
in hard disk drives. Extensive programmable control features and
system diagnostics are provided via a serial interface under the
direction of an external microcontroller. The large-scale integration
and use of advanced DABiC™ (digital/analog-BiCMOS) merged
technologies results in minimum power dissipation, minimum operating
voltage requirements, and minimum external components.
BACK-EMF and
COMMUTATION LOGIC
8
SPIN-DEMAND
12
SERVO-DEMAND
The spindle drive function incorporates a three-phase MOS power
driver and a back-EMF sensing motor commutation scheme. Internal
logic and analog circuitry provide complete start-up and µC-assisted
run modes without the need for snubbers or other external components. Additional headroom is achieved by a proprietary circuit, which
eliminates the need for an external current-sense resistor. Intrinsic
ground clamp and flyback diodes are also provided.
SERVO CONTROL
ADJUST
VOLTAGE REF.
V REF(X2)
V REF
ENERGY MANAGER
SERIAL INTERFACE
T
C
U
Y
D
L
O
N
R
P EO
D
C
E
N
U
E
N
I
R
T
E
N
F
E
O
R
C
S
I
R
D FO
—
SER DATA IN
Dwg. PP-048
Dwg. PP-048
ABSOLUTE MAXIMUM RATINGS
at TA = +25°C
Load Supply Voltage, VCC(PWR) .......... 7.0 V
Spindle Output Current, IOUT(S) ......... ±1.6 A
Voice-Coil Output Current, IOUT(S) .... ±0.9 A
Output Current, IOUT(S) ...................... ±1.6 A
Logic Supply Voltage VCC(D) ............... 6.0 V
Operating Temperature Range,
TA ..................................... 0 °C to +70°C
Output current rating may be restricted to a value
determined by system concerns and factors.
These include: system duty cycle and timing,
ambient temperature, and use of any heatsinking
and/or forced cooling.
The voice-coil function contains a 12-bit DAC, tunable low-pass
and notch filters, and a full-bridge power driver. The MOS outputs
provide increased available voltage and lower power dissipation over
bipolar devices. Voice-coil current is sensed by internal circuitry that
eliminates the need for an external current-sense resistor. Additional
internal circuitry can be configured to provide an over-velocity fault
limit by utilizing the internally monitored current of the voice-coil motor.
The spindle and voice-coil control functions are supplemented by
an ENERGY MANAGER™ subsystem, which efficiently channels available
power to protect the heads and the data disk during system failure or
normal system shutdown. Synchronous rectification of spindle
back-EMF voltage provides nearly lossless conversion of spindle
rotational inertia into power to operate the voice coil motor for parking
the heads. A dc-to-dc converter provides continuous operation at
minimum supply voltages. In addition, the E NERGY MANAGER subsystem
provides several sleep modes and latched fault states for undervoltage
or thermal faults.
The A8980CJT is supplied in a 64-lead thin quad flatpack for
surface-mount applications.
FEATURES
Voice Coil Motor Driver:
■ Low rDS(on) MOS Outputs
■ Lossless Current Sensing
■ Zero Deadband
■ User-Adjustable Transconductance Gain
■ Retract Circuitry Functional to 0 V
8980
SUPERSERVO™
SPINDLE & VOICE-COIL
ACTUATION MANAGER/DRIVER
FUNCTIONAL BLOCK DIAGRAM
POWER-ON
RESET (TO µC)
ENERGY MANAGER
V
REF
2V
REF
CONTROLLED RETRACT
DC-DC CONVERSION
SLEEP MODES
UV FAULT
THERMAL SHUTDOWN
OVER-VELOCITY FAULT
gm
SERVO CONTROL
R
NOTCH
FREQUENCY,
DEPTH, &
DAMPING
gm
TUNABLE
LOW-PASS
FILTER
12-BIT
SERVODEMAND
DAC
µC SERIAL INTERFACE
UV TRIP ADJUST
SERIAL DATA IN
CLOCK
DATA ENABLE
2 MHz CLOCK
RETRACT
R gm
g
m
SLEW
RATE
CONTROL
8-BIT
SPIN-DEMAND
DAC
IN / OUT MUX
ANALOG MUX 1
ANALOG MUX 2
CONFIGURATION
CONTROL
BACK-EMF AND
COMMUTATION LOGIC
DIGITAL MUX OUT
EXTERNAL
COMMUTATION
TACH
Dwg. FP-028B
Spindle Motor Controller/Driver:
■ Low rDS(on) MOS Outputs
■ Back-EMF Circuitry Eliminates Hall-Effect Sensors
■ Programmable Slew Rate Eliminates Snubbers
■ Lossless Current Sensing
■ Improved Speed Disturbance Performance
■ Dynamic Braking with Delay
■ Active Braking
Servo Compensator/Notch:
■ Over-Velocity Fault Circuitry
■ 12-Bit Servo-Demand DAC
■ Programmable Complex Pole Low-pass-Filter
■ Programmable Notch Frequency, Depth, and Damping
Energy Manager:
■ 3.0 V to 5.5 V Operation
■ Independent Power-Down (Sleep) Modes for all
Functional Blocks
■ Efficient Synchronous Rectification Supplies Power
During Blackout
■ Thermal Fault Shutdown Circuitry
■ Trimmed Bandgap Voltage Reference
■ Smart DAC Reference Generator
■ Programmable Voltage Reference for Relative Ground
■ Over-Velocity Fault Circuitry
■ Supply Under-Voltage Monitor with Adjustable
Trip Point
■ System Diagnostics Data Out
■ Power-On Reset Generator
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
Copyright © 1992, 1994, Allegro MicroSystems, Inc.
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, nonintrinsic complex-pole low-pass filter is
provided to attenuate undesirable, out-ofband 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.
V BOOST(L)
V CC(A)
V BG
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 transconductance 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 A/V
Rgm(act)
and I OUT = 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.
VCC(PWR)
VM
V CC(A)
UNDER-VOLTAGE
FAULT
L FLYBACK
DC-TO-DC
CONVERTER
V DC+ VM
V BOOST(H)
TRIP ADJ
VCC(D)
V BOOST(H)
V BOOST(L)
POWER
ON
RESET
ADJUST
(FROM SERIAL
INTERFACE)
FILTERED
V VEL
V REF +
V REF -
V REF
2
V REF
V BG
V BOOST(L)
V DC
POR
OUT
RETRACT
VOLTAGE
REFERENCE
VOICE-COIL
DRIVER
V RETRACT
SPINDLE
MOTOR DRIVERS
V BOOST(L)
VCC(A)
OVER VELOCITY
FAULT
V BOOST(L)
V BOOST(H)
RETRACT
MODE
BANDGAP
VOLTAGE
REFERENCE
V BOOST(L)
V BG
REFERENCE
ADJUST
V CC(A)
VCC(A)
2
÷2
VCC(D)
TJ
V BG
ADJUST
(FROM SERIAL INTERFACE)
THERMAL
FAULT
V REF(x2)
x2
SHUTDOWN /
SLEEP
V REF
8980
SUPERSERVO™
SPINDLE & VOICE-COIL
ACTUATION MANAGER/DRIVER
SPINDLE
heads, actuator retract mode controlled by constant voltage, and
several sleep modes. In addition, a power-on reset function and two
programmable voltage references (VREF and V REF(x2)) are provided that
are suitable for output to the user.
The spindle function is a three-phase
back-EMF sensing motor controller and
driver. During start-up, internal circuitry
provides complete spindle control and drive.
At speed however, an external
microcontroller is used to provide speed
(phase/frequency) detection as well as
compensation.
An onboard dc-to-dc converter generates two regulated “high”
(greater than the supply) voltages referred to as VBOOST(H) and VBOOST(L).
These voltages supply critical functions with maximum immunity from
supply variations.
SERIAL INTERFACE
ENERGY MANAGER
The management of available energy
is provided by automatic operating modes
envoked by the fault monitor or sleep-mode
manager. The fault monitor consists of an
over-velocity fault circuit, a VCC(A) undervoltage fault circuit, and a thermal fault circuit.
The operating modes include VCC(PWR) isolation, active rectification of spindle back-EMF
voltage to provide nearly lossless conversion
of spindle rotational inertia into power to
operate the voice-coil motor for parking the
The serial interface is used to alter the control state of the device
from an external microcontroller or other digital CMOS source.
In addition to the various operational and diagnostic control states
(modes), all critical constants, variables, and parameters can be
adjusted through this interface. The serial interface is a synchronous
serial three-wire port with serial data input, clock, and load (active low)
functions. When LOAD is high, the serial interface is disabled and the
chip is not affected by changes in SER DATA IN or CLK SER. To
write data to the serial interface, CLK SER should be low prior to
LOAD going low. Once LOAD goes low, information at SER DATA IN
is read into the shift register on the positive-going transitions of
CLK SER.
TERMINAL FUNCTIONS
ANALOG SUPPLY
VCC(A) ; supplies all analog functions except for gate drive of power output transistors. For most
applications, VCC(A) , VCC(D), and VCC(PWR) are connected together.
DIGITAL SUPPLY
VCC(D); supplies all digital functions. For most applications, V CC(A), VCC(D), and VCC(PWR) are
connected together.
LOAD SUPPLY
VCC(PWR); supplies all voice-coil and spindle power output transistors. This terminal is internally
connected to the source of the blocking FET used to isolate VM from V CC(PWR) on system failure
or shutdown. For most applications, VCC(A), VCC(D), and VCC(PWR) are connected together.
SUB
Substrate. This terminal must be connected to ground.
VM
Supplies power to the voice-coil and spindle power output transistors. Connect this terminal to
the external flyback inductor for the dc-to-dc converter; internally connected to the drain of the
blocking FET.
LFLYBCK
External inductor for the dc-to-dc converter.
VBOOST(H)
Internally generated “high” voltage for driving the gates of all source-side power output
transistors. This source is regulated and requires a compensation capacitor from this terminal
to ground.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
8980
SUPERSERVO™
SPINDLE & VOICE-COIL
ACTUATION MANAGER/DRIVER
VBOOST(L)
Internally generated intermediate voltage for driving the gates of all sink-side power output
transistors, the bandgap reference, and fault monitors. This source is regulated and requires
a compensation capacitor from this terminal to ground.
VPF(GATE)
Control voltage provided to drive the gate of an optional external enhancement-mode power
FET, augmenting the internal blocking FET between VCC(PWR) and VM.
VREF
Programmable reference voltage output. This reference tracks VREF(x2) and may be used as a
relative signal ground.
VREF(x2)
Programmable reference voltage output. Derived from a trimmed internal bandgap reference.
May be used as the reference for system DAC and ADC.
POROUT
Power-on reset for the application system. Active low guaranteed by design to be active on
power up. Also occurs as a result of VCC(A) degrading below the BLACKOUT under-voltage
threshold.
TRIP ADJ
VUV (TRIP) ; trip threshold adjust input (an external resistor divider between VCC(A) and ground) for
the under-voltage BLACKOUT fault monitor. A capacitor at this terminal can provide for time
domain filtering.
CLK
fCLK(2MHz); reference for all internal analog signal-processing functions. Affects frequency
domain placement of all poles, zeros, and bandwidths.
SER DATA IN
Non-inverting microcontroller serial-data input used for transferring data to all internal parameter
and mode-control registers.
CLK SER
fCLK(SER); reference for the serial data interface. Data is transferred on the positive-going edge
of this clock.
LOAD
Active low. Begins and ends data transfer.
EXT XFR
Direct clock gating data from temporary internal latch to control register. This continuous time
input is redundant to the XFR bit, which is embedded in the serial data format. It is internally
synchronized to the fCLK(2MHz) positive-going edge.
AMUX1
Analog input or output. Also used to drive internal nodes.
AMUX2
Analog input or output. Also used to drive internal nodes for calibration and measurement on
internal analog functions.
DMUXOUT
Non-inverting digital multiplexer output. Used to probe internal nodes allowing precise timedomain measurements. Also used to extract internal status and diagnostic information.
OUTP
VOUT(P); voice-coil power output. Full-bridge differential complement to VOUT(N).
OUTN
VOUT(N) ; voice-coil power output. Full-bridge differential complement to VOUT(P).
VSENS(act)
The voltage at this terminal is proportional to voice-coil actuator current.
8980
SUPERSERVO™
SPINDLE & VOICE-COIL
ACTUATION MANAGER/DRIVER
Rgm(act)
A resistor between this terminal and VSENS(act) is used to adjust the forward transconductance
gain of the voice-coil transconductance amplifier.
RETRACT
Active high retract input from the system. Continuous-time direct input to cause immediate
retract mode.
EXT ACT
VSERVO ; summing junction at the input of the voice-coil transconductance amplifier. This direct
continuous-time input to the actuator gm amplifier provides diagnostic as well as feed-forward
access.
OP1(IN)
Operational amplifier inverting input. The non-inverting input is internally connected to VREF.
OP1(OUT)
Operational amplifier output. This undedicated operational amplifier functions in continuous time.
VELINN
Inverting input of operational amplifier portion of over-velocity fault circuit.
VELINP
Non-inverting input of operational amplifier portion of over-velocity fault circuit.
VEL
VVEL; output of the over-velocity operational amplifier. Also internally connected to the inputs of
two comparators that provide the positive and negative velocity fault thresholds.
OUTA
VOUT(A); spindle motor power output terminal.
OUTB
VOUT(B); spindle motor power output terminal.
OUTC
VOUT(C) ; spindle motor power output terminal.
C TAP
Connection to spindle motor center tap; provides the differential reference for detection of backEMF zero crossings. If this terminal is not connected, the device will internally simulate the
centertap of the motor.
VSENS(spin)
The voltage at this terminal is proportional to the spindle motor current.
Rgm(spin)
A resistor connected from this terminal to VSENS(spin) provides for adjusting the forward
transconductance gain of the spindle transconductance amplifier.
fcom
A digital logic output that goes low to high on a back-EMF zero crossing; provides tach-like
information to the spin controller.
EXT COM
fsync; hard external commutation sequence start (positive-edge triggered). May be used to place
spindle commutation edges in the inter-sector gap, or for phase-locking multiple spindle drivers.
EXT SPIN
mand
Vspin; direct continuous time input to the spindle transconductance amplifier/driver. Zero decurrent occurs at 2.00 V; full-scale positive demand current occurs at 4.00 V.
SWIN
Input for uncommitted analog switch.
SWOUT
Output of uncommitted analog switch.
SWON
Logic input for uncommitted analog switch; a high level connects SWIN to SWOUT.
115 Northeast Cutoff, Box 15036
Worcester, Massachusetts 01615-0036 (508) 853-5000
8980
SUPERSERVO™
SPINDLE & VOICE-COIL
ACTUATION MANAGER/DRIVER
ADDRESS MAP AND DATA BIT ASSIGNMENTS
Address
Word
Data
Bit
Function
00H
0–3
4–7
Blanking Time
Commutation Delay Time
01H
0–5
6
7
Coast Time
Commutation Multiplexer
Not used at this time
0–3
4–7
Startup Time
Watchdog Time
0–7
8
Spindle-Demand DAC Current
Magnitude
Reverse Commutation Mode
04H
0–3
4–6
7
Spindle Slew Rate Control
Spindle Multiplexer
Not used at this time
05H
0–3
Spindle Transconductance Amp.
Bandwidth
Spindle Transconductance Amp.
Local Zero
02H
03H
4–6
06H
4–7
Internal 6.25 kHz Oscillator
Frequency Trim
Not used at this time
07H
0–7
Not used at this time
08H
0 – 11
Servo-Demand DAC Current
Magnitude
09H
0–7
Not used at this time
0AH
0–3
4
5
6–7
Low-Pass Filter Damping (Zeta)
Control
Not used at this time
Low-Pass Filter Reset Control
Not used at this time
0–3
4–7
Notch Depth (α3) Control
Not used at this time
0BH
0–3
Address
Word
Data
Bit
Function
0CH
0–3
4
5–7
Notch Width (Zeta DZ3) Control
Notch Reset Control
Not used at this time
0DH
0–4
Low-Pass Filter Freq. Synth.
(Dn2 ) Control
Not used at this time
5–7
0EH
0–4
5–7
0FH
0–3
4–6
7
10H
0–2
3–5
Notch Center Frequency
(Dn3 ) Control
Not used at this time
Actuator Bandwidth
(BWACT) Control
Actuator Zero (Damping) Control
Not used at this time
6–7
Retract Velocity Demand Voltage
Actuator Analog Multiplexer Input
Select
Not used at this time
11H
0–7
Sleep Mode Manager
12H
0–3
4–6
Fault Control Monitor
Programmable References
Voltage Select
Long Spindle Braking Delay
7
13H
0–2
3–5
6–7
14H
0–2
3
4
5–7
15H
0-2
Analog Multiplexer-2 Selection
Digital Multiplexer Output
Selection
Not used at this time
Analog Multiplexer-1 Selection
Chopper Stabilization of LP &
Notch Filters
Disable actuator retract during
fault
Not used at this time
Actuator Power Voltage Amplifier
Deadband Trim
8980
SUPERSERVO™
SPINDLE & VOICE-COIL
ACTUATION MANAGER/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
Similar pages