8932-A

8932-A ALLEGRO

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Technical content

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 exter- nal 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. VOICE-COIL MOTOR DRIVER

FEATURES

I Class-B, 2 Ω rDS(on) at 500 mA Output I Lossless Current Sensing I Zero Current-Loop Deadband I High Transconductance Bandwidth I User-Adjustable Transconductance Gain I Digital Transconductance Gain Switch (4:1 Ratio) I 5 Volt Monitor with Selectable UV Trip Point I Retract Circuitry Functional to 0 Volts I Sleep Mode Function I Internal Back-EMF Velocity Loop Option I Internal Thermal Shutdown Circuitry Data Sheet26300.2A† Always order by complete part number, e.g., A8932CLWA . ABSOLUTE MAXIMUM RATINGS Analog Input Voltage Range, Logic Input Voltage Range, Package Power Dissipation, Operating Temperature Range, Storage Temperature Range, † 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. 14 15 RET SET LOAD SUPPLY ACT REFERENCE H GAIN PWR OFF RET REF GROUND SWITCH OUT SIGNAL SUPPLYOUTSW IN N R OUT P UVSET VBEMF V FLT CCV VSENS V LOAD VSENS FB SGND N OUTP OUTN VDD SGND P ACT FB Dwg. PP-042B RETRACT FAULT MP RESET 2 V – + – + V REF PROTECT CIRCUIT PROTECT CIRCUIT 8932-A

115 Northeast Cutoff, Box 15036

Worcester, Massachusetts 01615-0036 (508) 853-5000 50 75 100 125 150 0.5 ALLOWABLE PACKAGE POWER DISSIPATION IN WATTSAMBIENT TEMPERATURE IN °C 2.0 1.5 1.0 Dwg. GP-034 FREE AIR,R = 66 °C/W θJA FUNCTIONAL BLOCK DIAGRAM Copyright © 1992, 1995 Allegro MicroSystems, Inc. ERROR AMP POWER AMP POWER CONTROL LOGIC CURRENT-SENSE AMP Dwg. FP-024D SENSE + I SENSE – I PROTECTION CIRCUITRY RETRACT CONTROL TSD SIGNAL SUPPLY LOAD SUPPLY VDDVCC VOLTAGE-SENSE AMP 2 V 14 22 REF. ACT REFERENCE H GAIN PWR OFF FAULT ACTFB MPRESET 13 SWITCH GROUND VBEMF UVSET VFLT RET SET RET REF ROUT P 53 2 28 16 11 RETRACT V LOAD OUTSW VSENS FB OUTP OUTN VSENS SGND P SGNDN IN N9 OUT7 REF. REF.

www.allegromicro.com ELECTRICAL CHARACTERISTICS at TA = +25°C, VCC = VDD = 5.0 V, VREF = VIN = 2.0 V, Load = 150 µH/3.5 Ω (unless otherwise noted). Limits Characteristic Symbol Test Conditions Min. Typ. Max. Units Error Amplifier Input Offset Voltage V IO ILOAD = 0 mA —— ±50 mV Current Gain A iH H GAIN ≥ 3.5 V 7200 8000 8800 — AiL H GAIN ≤ 0.7 V 1800 2000 2200 — Current Gain Linearity E L(adj) IOUT = 5 mA to 500 mA, Ai = AiL —— ±10 % IOUT = 5 mA to 500 mA, Ai = AiH —— ±10 % Reference Voltage Range V REF 1.5 — 2.5 V Voltage-Sense Amplifier Voltage Gain A VD 0.36 0.40 0.44 — Output Offset Voltage V OO ILOAD = 0 mA —— ±25 mV Current-Sense Amplifier Amplifier Error E VD (Rs x ILOAD / (Ai x VSENSE)) - 1 — 1.0 —— Input Offset Voltage V iO ILOAD = 0 mA, Ai = AiL —— ±25 mV Output Drivers Total On Resistance rDS(on) ILOAD = 100 mA — 2.0 2.5 Ω (Source + Sink) I LOAD = 500 mA — 2.0 2.5 Ω Retract Output Voltage Error E OUT(PN) VOUT(P) - VOUT(N) - VRETSET —— ±100 mV Full Power Bandwidth BW -3 dB 1.0 —— kHz Uncommitted Op Amp Voltage Gain A VS — 91 — dB Unity Gain Bandwidth BW — 1.0 — MHz Max. Load Capacitance C LOAD — 40 — pF Slew Rate SR — 4.2 — V/µs Output Voltage V O VSWITCH ≤ 0.7 V 2.5 — 3.5 V VOSW VSWITCH ≥ 3.5 V 2.5 — 3.5 V Max. Output Current I O — ±250 — µA Input Offset Voltage V IO — <±10 — mV Continued next page… Negative current is defined as coming out of (sourcing) the specified device terminal. Typical Data is for design information only.

Worcester, Massachusetts 01615-0036 (508) 853-5000 Miscellaneous Supply Voltage V CC Operating 4.5 5.0 5.5 V VDD Operating 4.5 5.0 5.5 V Under-Voltage Lockout Voltage V CC VCC = VDD 3.9 4.2 4.35 V Fault Logic Output V FAULT VRETRACT ≥ 3.5 V —— 500 mV VRETRACT ≤ 0.7 V 4.5 —— V IFAULT VFLT = 2.25 V — >20 — µA Power-On Reset V MPRESET VRETRACT ≥ 3.5 V 4.5 —— V VRETRACT ≤ 0.7 V, IMPREST = 1.5 mA —— 800 mV Total Supply Current I CC + IDD Outputs Balanced, No Load —— 10 mA Sleep Mode, PWR OFF = VCC —— 2.0 mA Logic Input Voltage V IN(0) —— 0.7 V VIN(1) 3.5 —— V Thermal Shutdown Temperature T J — 165 — °C Thermal Shutdown Hysteresis ∆TJ — 20 — °C ELECTRICAL CHARACTERISTICS at TA = +25°C, VCC = VDD = 5.0 V, VREF = VIN = 2.0 V, Load = 150 µH/3.5 Ω (unless otherwise noted). Limits Characteristic 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 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 responsi- bility for its use; nor for any infringement of patents or other rights of third parties which may result from its use.

www.allegromicro.com Term. Terminal Name Function 1 RET REF The reference supply for setting the voltage across the load during retract. 2V FLT Reservoir (energy storage) capacitor used to operate fault circuitry. 3V BEMF Back-EMF voltage from spindle motor used to retract heads during loss of power. 4 GROUND Circuit reference. 5U V SET Under-voltage trip point reference input. Set internally to 4.2 V but may be overridden by external resistor divider. (Equation 4). 6R OUT P Source driver used for retract; externally connected to OUTP. 7 OUT Output of uncommitted operational amplifier. 8 SWITCH Logic input for transmission gate; a high level connects OUT to OUT SW. 9I N N Inverting input to uncommitted operational amplifier. 10 OUT SW Transmission-gated output of uncommitted operational amplifier. 11 RETRACT An active-low logic input that initiates the retract sequence.

12 FAULT A logic low at this MOS output indicates a thermal shutdown, under-voltage fault, or retract

command.

13 MP RESET (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. 14 SIGNAL SUPPLY V CC; low-current supply voltage in the range of 4.5 V to 5.5 V. 15 ACT Input which controls the current in the load. Transconductance gain is set with an external resistor in series with this input (Equation 1). 16 REFERENCE V REF; reference input for all amplifiers; ac ground.

17 H GAIN Logic input to switch the error amplifier transconductance gain: LOW = 2000,

HIGH = 8000. 18 PWR OFF An active-high logic input that puts the device in a “sleep mode”. All fault circuitry remains active. 19 ACT FB Input connection for feedback network which sets the error amplifier gain and bandwidth. 20 SGND P Power ground for the OUTP sink driver. 21 OUT N Power output. Sinks current when VACT < VREF. 22 LOAD SUPPLY V DD; high-current supply voltage for the voice-coil motor. 23 OUT P Power output. Sinks current when VACT > VREF. 24 SGND N Power ground for the OUTN sink driver.

25 V SENS FB Input connection for feedback network which sets the current-sense amplifier gain and

bandwidth. Also called gm SET. 26 V LOAD An output voltage proportional to the load voltage. Used in conjunction with closed-loop velocity control. 27 V SENS Voltage output representing load current (Equation 2). Also called MONITOR. 28 RET SET An external resistor divider to set the retract voltage across the load. Used in conjunction with VRET-REF (Equation 3). TERMINAL FUNCTIONS

Worcester, Massachusetts 01615-0036 (508) 853-5000

0.4 R /R1 2

A = 2000 or 8000 VBEMF A i K /JT1 / S K B 1/RVgm Ø Ø i 1/RgmVIN Dwg. OP-003B Current Amplifier. The A8932CLWA voice-coil motor driver features a wide transcon-ductance bandwidth and minimal crossover distortion. The transconductance gain is user selectable: (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 Z 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 imple- mented. The first of these amplifiers provides a voltage output that is proportional to the load current: (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. DEVICE DESCRIPTION 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 V LOAD 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: where Ai = 2000 (H GAIN = logic Low) VSENSE = RS ILOAD Ai VLOAD = -AVD ([ILOAD RLOAD] + VBEMF) 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. VSENSE = RS ILOAD/AiL gm = Ai Rgm OUTSW = 0.4 (VBEMF R1/R2) R2 RS

0.4 Ai RLOAD

R3 = VBEMF VIN R1 KB KT Ai 2π RVGM R2 JBW = 0.4 R2 RVgm

0.4 Rgm R1

www.allegromicro.com 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 V IN in conjunction with OUTSW back-EMF voltage if no fault condition exists. If a fault condition were to occur how- ever, the retract velocity would be controlled by applying a constant user-defined voltage across the load: (Equation 3) where R7 + R8 >> 1000 Ω. 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. Power for the retract function is provided by the rectified back EMF of the spindle motor by way of the V BEMF terminal. The A8932CLWA will perform the retract func- tion 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. Under- voltage 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: (Equation 4) where R5 + R6 << 200 kΩ. 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. 2 (R 5 + R6) UVTRIP = TEST CIRCUIT AND TYPICAL APPLICATION 2 R8 1000 + R7 + R8 VRET-SET = VOLTAGE-SENSE AMP VOICE COIL MOTOR RZ H GAIN PWR OFF SWITCH ERROR AMP POWER AMP POWER CONTROL LOGIC PROTECTION CIRCUITRY CURRENT-SENSE AMP V REF VREF VDDVCC Dwg. EP-041D Rgm CZ R R +5 V RS R C2 R R R Vgm X VIN X 2 V SENSE + I SENSE – I TSD RETRACT CONTROL VCC VDD DIODE FOR RETRACT FUNCTION OTHERWISE SHORT TO SUPPLY BACK EMF FROM SPINDLE MOTOR R ≥ 200 kΩ FAULT RETRACT V = 2 V REF VREF

Worcester, Massachusetts 01615-0036 (508) 853-5000 Dimensions in Inches (for reference only) Dimensions in Millimeters (controlling dimensions) 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. 0° TO 8° 1 2 30.020 0.013 0.0040 MIN. Dwg. MA-008-28A in 0.050 BSC 28 15 0.0125 0.0091 0.050 0.016 0.2992 0.2914 0.419 0.394 0.7125 0.69690.0926 0.1043 0° TO 8° 2 3 18.10 17.70 0.51 0.33 2.65 2.35 0.10 MIN. 0.32 0.23 1.27 0.40 Dwg. MA-008-28A mm 1.27 BSC 7.60 7.40 10.65 10.00