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8932-A
RET REF V FLT V BEMF GROUND UV SET R OUT P OUT SWITCH IN N OUT SW RETRACT FAULT MP RESET SIGNAL SUPPLY 1 2 3 4 5 6 7 8 28 27 RET SET V SENS V LOAD V SENS FB SGND N OUTP LOAD SUPPLY OUT N SGND P ACT FB PWR OFF H GAIN REFERENCE ACT
VOICE-COIL MOTOR DRIVER
Providing control and drive of the voice-coil motor used for head positioning in 5 V disk drive applications, the second-generation A8932CLWA is a full-bridge driver that can be configured so that its output current is a direct function of an externally applied control voltage or current. This linear current control function is supplemented by additional circuitry to protect the heads and the data disk during system failure or normal system shutdown. The two 500 mA MOS driver outputs provide very low saturation voltage and minimal power dissipation. Additional headroom is achieved by the sense-FET structure eliminating the need for an external current-sense resistor. Internal circuitry can be configured to provide closed-loop velocity control of the actuator by utilizing the generated back-EMF of the voice-coil motor. Thermal protection and under-voltage lockout disables the system in a controlled sequence if a fault condition occurs.
Data Sheet 26300.2A
PROTECT CIRCUIT
-
26
+
25 24 23 VDD 22 21
-
9 10 11 12 13 14
+
V REF
-
2V
+
20 19 18 17
PROTECT CIRCUIT
+ -
16 15
V CC
FEATURES
I I I I I I I I I I I Class-B, 2 rDS(on) at 500 mA Output Lossless Current Sensing Zero Current-Loop Deadband High Transconductance Bandwidth User-Adjustable Transconductance Gain Digital Transconductance Gain Switch (4:1 Ratio) 5 Volt Monitor with Selectable UV Trip Point Retract Circuitry Functional to 0 Volts Sleep Mode Function Internal Back-EMF Velocity Loop Option Internal Thermal Shutdown Circuitry
Dwg. PP-042B
ABSOLUTE MAXIMUM RATINGS
Supply Voltages, VCC and VDD ............ 6.0 V Output Current, IOUT (peak) ........... 600 mA (continuous) ........................... 500 mA Analog Input Voltage Range, VIN .................................... -0.3 V to VCC Logic Input Voltage Range, VIN ............................... -0.3 V to +6.0 V Package Power Dissipation, PD ......................................... See Graph Operating Temperature Range, TA ..................................... 0C to +70C Junction Temperature, TJ ............... +150C Storage Temperature Range, TS ................................ -55C to +150C
Fault conditions that produce excessive junction temperature will activate device thermal shutdown circuitry. These conditions can be tolerated, but should be avoided. 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. For reliable operation the specified maximum junction temperature should not be exceeded.
Always order by complete part number, e.g., A8932CLWA .
8932-A VOICE-COIL MOTOR DRIVER
FUNCTIONAL BLOCK DIAGRAM
SIGNAL SUPPLY
14
LOAD SUPPLY
22
V CC ACT FB
19 I SENSE +
VDD
VOLTAGE-SENSE AMP
- +
26 20 23 21 24
V LOAD SGND P OUT P OUT N SGND N V SENS FB V SENS IN N OUT OUT SW
ACT 15 REFERENCE 16 H GAIN 17
ERROR - AMP
POWER AMP
REF.
+
2V POWER CONTROL LOGIC
+ -
PWR OFF 18
CURRENT-SENSE AMP
I SENSE -
25 27 9 7
- +
TSD FAULT 12 MP RESET 13 PROTECTION CIRCUITRY RETRACT CONTROL
REF.
-
REF.
6 4
10
+
8
5
3
2
28
1
11
RETRACT
VBEMF
UVSET
RET REF
RET SET
R OUT P
VFLT
GROUND
SWITCH
Dwg. FP-024D
ALLOWABLE PACKAGE POWER DISSIPATION IN WATTS
2.0
1.5
/W R, C AI 66 EE = FR JA R
1.0
0.5
0
25
50 75 100 125 AMBIENT TEMPERATURE IN C
150
Dwg. GP-034
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000 Copyright (c) 1992, 1995 Allegro MicroSystems, Inc.
8932-A VOICE-COIL MOTOR DRIVER
ELECTRICAL CHARACTERISTICS at TA = +25C, VCC = VDD = 5.0 V, VREF = VIN = 2.0 V, Load = 150 H/3.5 (unless otherwise noted).
Limits Characteristic Error Amplifier Input Offset Voltage Current Gain VIO AiH AiL Current Gain Linearity EL(adj) ILOAD = 0 mA H GAIN 3.5 V H GAIN 0.7 V IOUT = 5 mA to 500 mA, Ai = AiL IOUT = 5 mA to 500 mA, Ai = AiH Reference Voltage Range Voltage-Sense Amplifier Voltage Gain Output Offset Voltage Current-Sense Amplifier Amplifier Error Input Offset Voltage Output Drivers Total On Resistance (Source + Sink) Retract Output Voltage Error Full Power Bandwidth Uncommitted Op Amp Voltage Gain Unity Gain Bandwidth Max. Load Capacitance Slew Rate Output Voltage AVS BW CLOAD SR VO VOSW Max. Output Current Input Offset Voltage IO VIO VSWITCH 0.7 V VSWITCH 3.5 V -- -- -- -- 2.5 2.5 -- -- 91 1.0 40 4.2 -- -- 250 <10 -- -- -- -- 3.5 3.5 -- -- dB MHz pF V/s V V A mV EOUT(PN) BW EVD ViO (Rs x ILOAD / (Ai x VSENSE)) - 1 ILOAD = 0 mA, Ai = AiL -- -- 1.0 -- -- 25 -- mV AVD VOO ILOAD = 0 mA 0.36 -- 0.40 -- 0.44 25 -- mV VREF -- 7200 1800 -- -- 1.5 -- 8000 2000 -- -- -- 50 8800 2200 10 10 2.5 mV -- -- % % V Symbol Test Conditions Min. Typ. Max. Units
rDS(on)
ILOAD = 100 mA ILOAD = 500 mA VOUT(P) - VOUT(N) - VRETSET -3 dB
-- -- -- 1.0
2.0 2.0 -- --
2.5 2.5 100 --
mV kHz
Continued next page...
Negative current is defined as coming out of (sourcing) the specified device terminal. Typical Data is for design information only.
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8932-A VOICE-COIL MOTOR DRIVER
ELECTRICAL CHARACTERISTICS at TA = +25C, VCC = VDD = 5.0 V, VREF = VIN = 2.0 V, Load = 150 H/3.5 (unless otherwise noted).
Limits Characteristic Miscellaneous Supply Voltage VCC VDD Under-Voltage Lockout Voltage Fault Logic Output VCC VFAULT Operating Operating VCC = VDD VRETRACT 3.5 V VRETRACT 0.7 V IFAULT Power-On Reset VMPRESET VFLT = 2.25 V VRETRACT 3.5 V VRETRACT 0.7 V, IMPREST = 1.5 mA Total Supply Current ICC + IDD Outputs Balanced, No Load Sleep Mode, PWR OFF = VCC Logic Input Voltage VIN(0) VIN(1) Thermal Shutdown Temperature Thermal Shutdown Hysteresis TJ TJ 4.5 4.5 3.9 -- 4.5 -- 4.5 -- -- -- -- 3.5 -- -- 5.0 5.0 4.2 -- -- >20 -- -- -- -- -- -- 165 20 5.5 5.5 4.35 500 -- -- -- 800 10 2.0 0.7 -- -- -- V V V mV V A V mV mA mA V V C C Symbol Test Conditions Min. Typ. Max. Units
Negative current is defined as coming out of (sourcing) the specified device terminal. Typical Data is for design information only.
The products described here are manufactured under one or more U.S. patents or U.S. patents pending. 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 performance, reliability, or manufacturability of its products. Before placing an order, the user is cautioned to verify that the information being relied upon is current. Allegro products are not authorized for use as critical components in life-support devices or systems without express written approval. The information included herein is believed to be accurate and reliable. However, Allegro MicroSystems, Inc. assumes no responsibility for its use; nor for any infringement 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
8932-A VOICE-COIL MOTOR DRIVER
TERMINAL FUNCTIONS
Term. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 Terminal Name RET REF VFLT VBEMF GROUND UVSET ROUT P OUT SWITCH INN OUTSW RETRACT FAULT MPRESET SIGNAL SUPPLY ACT REFERENCE H GAIN PWR OFF ACTFB SGNDP OUTN LOAD SUPPLY OUTP SGNDN VSENS FB VLOAD VSENS RET SET Function The reference supply for setting the voltage across the load during retract. Reservoir (energy storage) capacitor used to operate fault circuitry. Back-EMF voltage from spindle motor used to retract heads during loss of power. Circuit reference. Under-voltage trip point reference input. Set internally to 4.2 V but may be overridden by external resistor divider. (Equation 4). Source driver used for retract; externally connected to OUTP. Output of uncommitted operational amplifier. Logic input for transmission gate; a high level connects OUT to OUTSW. Inverting input to uncommitted operational amplifier. Transmission-gated output of uncommitted operational amplifier. An active-low logic input that initiates the retract sequence. A logic low at this MOS output indicates a thermal shutdown, under-voltage fault, or retract command. (Power-On Reset) A logic low at this open-collector output may be used to reset the system on under-voltage fault or power on. VCC; low-current supply voltage in the range of 4.5 V to 5.5 V. Input which controls the current in the load. Transconductance gain is set with an external resistor in series with this input (Equation 1). VREF; reference input for all amplifiers; ac ground. Logic input to switch the error amplifier transconductance gain: LOW = 2000, HIGH = 8000. An active-high logic input that puts the device in a "sleep mode". All fault circuitry remains active. Input connection for feedback network which sets the error amplifier gain and bandwidth. Power ground for the OUTP sink driver. Power output. Sinks current when VACT < VREF. VDD; high-current supply voltage for the voice-coil motor. Power output. Sinks current when VACT > VREF. Power ground for the OUTN sink driver. Input connection for feedback network which sets the current-sense amplifier gain and bandwidth. Also called gm SET. An output voltage proportional to the load voltage. Used in conjunction with closed-loop velocity control. Voltage output representing load current (Equation 2). Also called MONITOR. An external resistor divider to set the retract voltage across the load. Used in conjunction with VRET-REF (Equation 3).
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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: gm = Ai Rgm
(Equation 1)
The back-EMF voltage represents the velocity of the actuator. By subtracting the ILOADRLOAD voltage component 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 VLOAD is proportional to the voltage across the load (AVD[VOUTN - VOUTP]). RS is selected so that VSENSE represents ILOAD while R3 is dependent on RLOAD as shown in the following equations: VLOAD = -AVD ([ILOAD RLOAD] + VBEMF) VSENSE = RS ILOAD/AiL where Ai = 2000 (H GAIN = logic Low) OUTSW = 0.4 (VBEMF R1/R2) R3 = R2 RS 0.4 Ai RLOAD
where Ai is either 2000 (H GAIN = Low) or 8000 (H GAIN = High). The error amplifier's bandwidth and load compensation 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 RZ and CZ for 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 implemented. The first of these amplifiers provides a voltage output that is proportional to the load current: VSENSE RI = S LOAD Ai
(Equation 2)
R2 RVgm VBEMF = 0.4 Rgm R1 VIN BW = 0.4 R1 KB KT Ai 2 RVGM R2 J
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.
where J is the moment of inertia, KB is the back-EMF motor constant, and KT is the torque constant. Velocity loop compensation = LLOAD/RLOAD = R1 C1 = R3 C2.
A i = 2000 or 8000 V IN 1/Rgm
+
-
1/R Vgm
Ai
KT /J
.. O 1/S
. O
KB
0.4 R1 /R2 K1 VBEMF
Dwg. OP-003B
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000
8932-A VOICE-COIL MOTOR DRIVER
Retract and Brake. A retract-brake sequence is initiated on receiving a fault indication from the internal thermal shutdown (TSD), or under-voltage lockout (UVLO), or an externally applied logic High at the RETRACT input. If the velocity control scheme is implemented, the head can be retracted under the full control of VIN in conjunction with OUTSW back-EMF voltage if no fault condition exists. If a fault condition were to occur however, the retract velocity would be controlled by applying a constant user-defined voltage across the load: VRET-SET = where R7 + R8 >> 1000 . When the sequence is operated, the output voltage is forced to approximately VRET-SET to retract the heads, and then a fault command ("brake") is sent to the spindle motor driver. The user determines the total time for the retract sequence, before the spindle brake is enabled, by the choice of an external resistor and capacitor at the FAULT output. 2 R8 1000 + R7 + R8
(Equation 3)
Power for the retract function is provided by the rectified back EMF of the spindle motor by way of the VBEMF terminal. The A8932CLWA will perform the retract function under low supply conditions (nominally down to 2 V). Operation down to almost 0 V requires an energy-storage capacitor at the VFLT terminal. Protective Features. The A8932CLWA has a number of protective features incorporated into the design. Undervoltage lockout provides system protection in the event of reduced primary supply voltages. The under-voltage trip point is internally set at approximately 4.2 V. It can be user-defined with an external resistor voltage divider: 2 (R5 + R6) R6 where R5 + R6 << 200 k. UVTRIP =
(Equation 4)
Thermal shutdown circuitry is included to protect the device from excessive junction temperature. It is only intended to protect the chip from catastrophic failures due to excessive junction temperature.
TEST CIRCUIT AND TYPICAL APPLICATION
+5 V RZ CZ V CC
I SENSE +
VDD
VOLTAGE-SENSE AMP
- +
V REF VOICE COIL MOTOR
V
Rgm IN
ERROR - AMP
POWER AMP
V REF = 2 V X H GAIN PWR OFF
+
2V
+ -
CURRENT-SENSE AMP
I SENSE -
POWER CONTROL LOGIC TSD
R2 RS C2 C1
- +
R 3
R FAULT 200 k
V REF
PROTECTION CIRCUITRY
RETRACT CONTROL VREF
- +
X R Vgm
R1
V CC
R7 R6 R8 VDD
RETRACT
R5
SWITCH
BACK EMF FROM SPINDLE MOTOR
DIODE FOR RETRACT FUNCTION OTHERWISE SHORT TO SUPPLY
Dwg. EP-041D
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8932-A VOICE-COIL MOTOR DRIVER
Dimensions in Inches (for reference only)
28 15 0.0125 0.0091
0.2992 0.2914
0.419 0.394
0.050 0.016 0.020 0.013
1
2
3 0.7125 0.6969
0.050
BSC
0 TO 8
0.0926 0.1043 0.0040 MIN.
Dwg. MA-008-28A in
Dimensions in Millimeters (controlling dimensions)
28 15 0.32 0.23
7.60 7.40
10.65 10.00
1.27 0.40 0.51 0.33
1
2
3 18.10 17.70
1.27
BSC
0 TO 8
2.65 2.35 0.10 MIN.
Dwg. MA-008-28A mm
NOTES: 1. Lead spacing tolerance is non-cumulative. 2. Exact body and lead configuration at vendor's option within limits shown. 3. Supplied in standard sticks/tubes of 27 devices or add "TR" to part number for tape and reel.
115 Northeast Cutoff, Box 15036 Worcester, Massachusetts 01615-0036 (508) 853-5000

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