www.fairchildsemi.com FAN8621B 12V Spindle Motor and Voice Coil Motor Driver IC Features Description General The FAN8621B, is a Bipolar monolithic stand-alone IC, designed for 12V HDD applications.The internal power stage consists of vertical PNP and NPN TRs for both SPM and VCM, thus minimizing voltage drop, and increasing drive capability up to 2A for SPM and 1.2A for VCM. This device includes soft commutation drive to reduce audible noise and intelligent retract function for decreased bouncing. • • • • Hysteresis power on reset with delay function 5V, 12V supplies monitoring Thermal shut down(TSD) Programmable precision regulator usging minimal external component • Three state control input to reduce number of PINs Spindle Motor(SPM) • • • • • • • • • • • ASIC based start-up Internal back-EMF processing Internal sensorless commutation Internal SPM speed control with SFLL(Syncronized Frequency Lock Loop). Linear SPM current control Selectable Motor Speed (5400/7200 RPM) Soft commutation circuitry to reduce acoustic noise Adjustable brake delay time Maximum 2A start-up current capability Internal and external spindle brake Speed lock indicator output 48-QFPH-1414 Voice Coil Motor (VCM) • • • • • Intelligent retract (decreased bouncing) 1.2A internal VCM power driver Selectable transconductance 4V precision reference output Two PWM input (fine/coarse) for VCM set point Typical Applications Ordering Information • Hard disk drive(HDD) Device Package Operating Temp. FAN8621B 48-QFPH-1414 0 ~ 70°C Rev. 1.0.0 May. 2000. ©2000 Fairchild Semiconductor International 1 FAN8621B Pin Assignments B 2 FAN8621B Pin Definitions Pin Number Pin Name IO Pin Function Description 1 VCNT A Speed controller output. Range 3.8V to 0.5V 2 CSOFT A Capacitor for soft commutation 3 ADJ A Adjust external regulator voltage (VREF) 4 SENSE5 A 5V power line sensing 5 VDD P 5V power line 6 FG O Frequency generation for spindle rotation speed. Typically 1.08KHz (5400RPM) 7 VREF P Regulator voltage output. This voltage is controlled by pin 3 voltage 8 CLK I System clock. Digital clock input as a time reference 9 HALFVCC P 1/2 VCC 10 POR O Power on reset. H : normal, L: power fail 11 CDLY A Define POR delay time 12 GAINSEL I Sense amplifier gain selection. H : High gain (8), L : Low gain (2) 13 PWMH I Coarse PWM input for VCM set point 14 PWML I Fine PWM input for VCM set point 15 CFVCM A Output of PWM inputs to voltage converter 16 VCMREF4V P 4V reference output for VCM 17 CRET A Define retract delay time. 18 VCC P 12V power line 19 FILOUT A Filtered output of PWM inputs. This voltage define VCM set point 20 SENSE A Non-inverting input of differential amplifier for VCM current sensing 21 CRET2 A Power for retract when power down 22 PVCC P 12V power line for VCM 23 VCM- A Negative output terminal of VCM power amplifier 24 RRET A Adjust maximum retract current 25 SENSEOUT A Output of differential amplifier for VCM current sensing 26 PGND P Ground for VCM 27 VCM+ A positive output terminal of VCM power amplifier 28 ERRIN A Inverting input of VCM error amplifier 29 VDD P 5V power line 30 ERROUT A Output of VCM error amplifier 31 SUBGND P Ground for spindle motor 32 W A Spindle W phase output 3 FAN8621B Pin Definitions (Continued) Pin Number Pin Name IO Pin Function Description 33 PCS A Spindle current sensing. 34 V A Spindle V phase output 35 SUBGND P Ground for spindle 36 N A Spindle N phase output 37 U A Spindle U phase output 38 PVCC P 12V power line for spindle 39 CCOMP A Current controller output. This Voltage define spindle output current 40 BRAKE A Gating signal for external brake 41 CBRAKE A Charged back-EMF to supply brake power when power down 42 SENSE12 A 12V power line sensing 43 GND P Ground 44 CNTL1 I Control input for spindle . H: spindle enable, Z: Spindle bias enable, L: brake 45 CNTL2 I Start-up clock and soft commutation. H: Start-up clock , L : soft commutation. 46 CNTL3 I Control input for VCM. H: VCM enable, Z : VCM disable, L: retract 47 READY O Speed lock indicator when speed is within 0.7% speed error range. H : speed locked, L: unlocked 48 RPMSEL I Target spindle speed selection. L : 5400 rpm, H: 7200 rpm with 5MHz Clock 4 FAN8621B Internal Block Diagram VCC CDLY POR 11 10 VREF ADJ 7 3 VDD VDD VCC 5 29 18 VDD TSD 25K SENSE12 42 SENSE5 4 7K CSOFT Retract External Brake U FG Generator 6 SPM bias enable CNTL2 CNTL3 44 Commutation Sequencing & Spindle Control SPM output on Three State Input Control 45 BRAKE 41 CBRAKE 38 PVCC 36 N 37 U 34 V 32 W 35 SUBGND 31 SUBGND 39 CCOMP U V W N SPM Three Phase Power Driver Back-EMF Processing & Zero Cross Detector Triangle Wave Generator 2 clock CNTL1 40 1.3V 11K 9K FG Bandgap Reference & Bias Power Management start-up clock hard/soft 46 Brake VCM on/off VDD Retract FG i spll Real Speed READY 47 RPMSEL 48 Speed Discriminator & Speed Lock Indicator 8 PWMH 13 PWML 14 CFVCM 15 GAINSEL 12 16 VCMREF4V VCC 22 PVCC 27 VCM+ 9 clock power amp PWMs Decorder & 2nd orderFilter U V VCM Gain Selection W sense amp VCM+ SENSE gain 2,8 VCMREF4V 24 23 VCM- 26 PGND 20 SENSE VCMREF4V Intelligent Retract 21 HALFVCC gain 14 Retract GND PCS error amp Counter & Timing Control 43 33 power amp 1 CLK VCMREF4V VCM H-bridge Power Driver i spll Speed Reference VCNT pre amp Current Limiting 17 19 28 CRET2 RRET CRET FILOUT ERRIN 5 30 ERROUT 25 SENSEOUT FAN8621B Absolute Maximum Ratings(Ta = 25°C) Parameter Symbol Value Unit Supply voltage (signal) VDD 6.0 V Supply voltage (signal) VCC 15.0 V Supply voltage (power) PVCC 15.0 V Storage Temperature TSTG −55 ~ 125 °C Power dissipation 3.0 PD note W Maximum Junction Temperature TJ 150 °C Operating Ambient Temperature TAMB 0 ~ 70 °C NOTE: 1. When mounted on 50mm × 50mm × 1mm PCB (Phenolic resin material) 2. Power dissipation is reduced 16mV / °C for using above Ta=25°C. 3. Do not exceed Pd and SOA(Safe Operation Area). Power Dissipation Curve Pd[mW] 3,000 2,000 1,000 0 0 25 50 75 100 125 150 175 Ambient temperature, Ta [°C] Recommanded Operating Coditions (Ta = 25°C) Parameter Symbol Min. Typ. Max. Unit Supply voltage (signal) VDD 4.5 5.0 5.5 V Supply voltage (signal) Vcc 10.8 12.0 13.2 V Supply voltage (power) PVCC 10.8 12.0 13.2 V 6 FAN8621B Electrical Characteristics (Ta=25°C, unless otherwise specified) Parameter Symbol Condition Min. Typ. Max. Unit IDD1 CNTL1=L,CNTL2=CNTL3=Z (brake) 80- 100 120 mA VDD Line supply current2 IDD2 CNTL1= CNTL2 =CNTL3=Z (SPM bias enable) 25 35 45 mA VDD Line supply current3 IDD3 CNTL1=CNTL3=H,CNTL2=Z (SPM,VCM enable) 25 35 45 mA VDD Line supply current4 IDD4 CNTL1=CNTL2=Z,CNTL3= L (retract) 25 35 45 mA VCC Line supply current1 ICC1 CNTL1=L,CNTL2=CNTL3=Z (brake) 2 7 12 mA VCC Line supply current2 ICC2 CNTL1= CNTL2 =CNTL3=Z (SPM bias enable) 4 9 15 mA VCC Line supply current3 ICC3 CNTL1=CNTL3=H,CNTL2=Z (SPM,VCM enable) 10 20 60 mA VCC Line supply current4 ICC4 CNTL1=CNTL2=Z,CNTL3=L (retract) 12 19 25 mA POWER SUPPLIES SUPPLY CURRENT VDD Line supply current1 SUPPLY MONITOR Threshold voltage1 for VCC VTH12A VCC=sweep,VDD=5V 9.05 9.40 9.75 V Threshold voltage2 for VCC VTH12B VCC=sweep,VDD=5V 8.75 9.10 9.45 V Hysteresis on VCCcomparator VHYS12 VCC=sweep,VDD=5V 0.15 0.3 0.45 V Threshold voltage1 for VDD VTH5A VCC=12V,VDD=sweep 3.45 3.90 4.15 V Threshold voltage2 for VDD VTH5B VCC=12V,VDD=sweep 3.30 3.75 4.00 V Hysteresis on V comparator VHYS5 VCC=12V,VDD=sweep 0.08 0.15 0.23 V ICPOR −18.0 −14 −10 µA VTHPOR 1.1 1.3 1.5 V POWER ON RESET GENERATOR Charging current for POR cap POR threshold voltage Output high voltage VPORH VCC = 12V, VDD= 5V, POR output current is 1mA 4.5 - Vdd V Output low voltage VPORL VCC = 12V, VDD= 5V, POR output current is 1mA 0 - 0.5 V CONTROL INPUTs(CNTL1,CNTL2,CNTL3) Control input low voltage VCTL CNTL1=CNTL2=CNTL3=sweep 0.8 1.3 1.7 V Control input high voltage VCTH CNTL1=CNTL2=CNTL3=sweep 1.85 2.3 2.75 V Control input low current ICTl CNTL1=CNTL2=CNTL3=sweep -290 -200 -110 µA Control input high current ICTH CNTL1=CNTL2=CNTL3=sweep 55 110 190 µA 7 FAN8621B Electrical Characteristics (Contnued) (Ta=25°C, unless otherwise specified) Parameter Symbol Condition Min. Typ. Max. Unit SPINDLE MOTOR (SPM) FG FREQUENCY GENERATOR FG frequency FFG CLK=5MHz,RPMSEL=L (5400 RPM) 0.97 1.08 1.18 KHz FG duty DFG FFG = 1.08KHz 45 50 50 % FG output high voltage VFGH FG output current is 1mA 4.5 - VDD V FG output low voltage VFGL FG output current is 1mA - - 0.5 V READY high output VRDH CNTL1=H,within ±0.7% motor speed error, 4.5 - VDD V READY low output VRDL READY output current is 1mA - - 0.5 V READY SIGNAL GENERATION SINDLE OUTPUT SATURATION VOLTAGE VSUU IU=1A 0.2 0.6 1.0 V VSaturation voltage upper VSVU IV=1A 0.2 0.6 1.0 V W Saturation voltage upper VSWU IW=1A 0.2 0.6 1.0 V U Saturation voltage lower VSUL IU=1A 0.2 0.4 0.8 V V Saturation voltage lower VSVL IV=1A 0.2 0.4 0.8 V W Saturation voltage lower VSWL IW=1A 0.2 0.4 0.8 V U Saturation voltage upper RPMSELECT INPUT RPMSEL threshold voltage VRPH - 1.1 1.5 1.7 V RPMSEL input high current IRPHI - 60 91 110 µA RPMSEL input low current IRPLO - -5 0 5 µA Speed controller high voltage VCNTH - 3.5 3.8 4.2 V Speed controller low voltage VCNTL - - - 0.5 V High voltage of linear range VLIMITH - 3.15 3.5 3.85 V Low voltage of linear range VLIMITL - 1.15 1.5 1.85 V F/I converter charge current ISPLLC - -70 -50 -40 µA F/I converter discharge current ISPLLD - 40 52 70 µA Transeconductance gain of SPM GMSPM RPCS=0.33Ω 0.6 0.8 1.0 - Limit voltage of current amp VLIMIT1 RPCS = 0.33Ω - 0.57 - V Limit voltage of current amp VLIMIT2 RPCS = 0.33Ω Equivalent output resistance RCC SPEED CONTROLLER CURRENT LIMITTER - - 0 - V - 20 - KΩ - 3.3 - V - - 2.0 % - - 2.0 % EXTERNAL REGULATOR Regulator output voltage VREG Regulator line regulation RLINE Regulator load regulation RLOAD VADJ(pin3) = 1.3V IO= 500mA 8 FAN8621B Electrical Characteristics (Contnued) (Ta=25°C, unless otherwise specified) Parameter Symbol Condition Min. Typ. Max. Unit SPINDLE MOTOR (Continued) BRAKE Cbrake output voltage VBC - 11 11.3 11.8 V Brake output high voltage VBH - 11 − − V Brake output low voltage VBL - - - 0.5 V Soft commutation high voltage VSOFTH - 3.1 - 3.7 V Soft commutation low voltage VSOFTL - 1.4 1.7 2.0 V Discharging current ISOFTC - 30 45 60 µA Charging current ISOFTD - -60 -45 -30 µA - - 1.8 V - −10 0 10 µA SOFT COMMUTATION DRIVE OUTPUTS (U,V,W) Total voltage Drop Leakage current VDROPS IMOTOR = 1A ILEAKS VOICE COIL MOTOR CIRCUIT(VCM) PWM INPUTS PWMH/PWML high input voltage VPWMH - 2.8 - - V PWMH/PWML low input voltage VPWML - - - 2.2 V PWMH charge/discharge current IPWMH - 650 670 690 µA PWML charge/discharge current IPWML - 10 10.5 11 µA PWM current ratio IRATIO 63 64 65 Internal resister RFVCM - - 3 - kΩ Maximum phase shift DF Measure at 500Hz, CCFVCM = 1nF - - −2 deg Cut-off frequency FCO - - 100 - KHz Attenuation at 1MHz FITER - - 70 - dB IPWMH/IPWML VCN PWM FILTER Filter output voltage1 VCVCM1 PWMH=PWML=0% 5.6 6.00 6.40 V Filter output voltage2 VCVCM2 PWMH=PWML=50% 3.8 4.0 4.2 V Filter output voltage3 VCVCM3 PWMH=PWML=100% 1.6 2 2.4 V VCM reference voltage 4V VREF4 CNTL3 = 5V, VREF4V output current=1mA 3.8 4 4.2 V VCM reference voltage 1/2 VCC VREF6 HALFVCC output current =1µA 5.9 6.0 6.1 V VCM REFERENCE 9 FAN8621B Electrical Characteristics (Contnued) (Ta=25°C, unless otherwise specified) Parameter Symbol Condition Min. Typ. Max. Unit VSOH - 10.8 - - V Amp low output voltage VSOL - - - 1.2 V Input offset voltage VOSS - −15 0 15 mV Short circuit current ISSC - 10 - - mA Unity gain bandwidth BGS - - 2 - MHz SENSE AMPLIFIER Amp high output voltage Voltage gain 1 AVS1 GAINSEL : L - 18 - dB Voltage gain 2 AVS2 GAINSEL : H - 6 - dB ERROR AMPLIFIER Amp high output voltage VEOH - 10.8 - - V Amp low output voltage VEOL - - - 1.2 V Input offset voltage VOSE - −15 0 15 mV Open loop gain AVE - - 80 - dB Unity gain bandwidth BGE - - 2 - MHz Short circuit current ISSE - 8 - - mA VPOH - 11.5 - - V Output low voltage VPOL - - - 0.5 V Input offset voltage VOSP - −15 0 15 mV Gain APO - 21.2 22 23.8 dB Unity gain bandwidth BGP - - 2 - MHz POWER AMPLIFIER Output high voltage Total voltage Drop Leakage current VDROPV when VCM current is 0.7A - - 1.5 V −20 0 20 µA PWMH=PWML=50% Duty −20 0 20 mA - ILEAKV VCM AMP TOTAL VCM offset current VVCMOS VCM transconductance low gain GMVH GAINSEL = H,sense resister is 1Ω 0.05 0.12 0.14 A/V VCM transconductance high gain GMVL GAINSEL = L,sense resister is 1Ω 0.35 0.45 0.55 A/V Min operating voltage of CRET2 VCRET2 - 2.0 - - V Cret charge current ICRET - -70 -85 -100 µA Max. retract sink current IRCT - - 125 - mA Retract reference voltage VRET - 0.75 0.9 1.05 V Retract current limit resister RIRET - - 3 - KΩ Leakage current of output TR ILRET - −10 0 10 µA VRTSAT - - 0.4 0.7 V Operating temperature TTSD - 135 150 165 °C Thermal hystereis THYS - 20 30 40 °C RETRACT FUNCTION Sink saturation voltage THERMAL SHUT DOWN 10 FAN8621B Application Informations General The FAN8621B is a stand alone combination chip consisting of Spindle Motor (SPM) and Voice Coil Motor (VCM)circuit for HDD applications. The speed control of SPM is achieved by internal Synchronous Phase Locked Loop (SPLL). The FAN8621B supplies adjustable regulated power with external component and signals READY indicating SPM is locked within some speed range (typically ±0.7% speed error). Current set point is applied by two PWM signals and VCM current is monitored by external sense resistor. VCM circuit generates 4 voltage references for testing. Fig.1 shows overall interfacing of FAN8621B with external and HDD motors POR Vreg3.3 Power Management CNTL1 CNTL2 CNTL3 Interface RPMSEL READY DIGITAL ASIC SPM FG PWMH PWML GAINSEL VCM VCMREF4V CLK Retract/Brake TSD Figure 1. Overall Interfacing of the FAN8621B The control signals have three status and their function is summarized as follows; Pin Status H Z L SPM enable(1) bias enable disable Brake disable disable enable Commutation hard Hard soft Start Clock high(2) low(2) - Signals CNTL1 CNTL2 CNTL3 GAINSEL VCM enable disable disable Retract disable disable enable Start-up hold normal normal hold(3) Sense Amp gain 2 2 8 Table 1. Control PIN function Notes: 1. SPM bias + SPM Output Driver enable 2. Makes SPM Open Loop (Start-up) Commutation Signal 3. Test Only when READY is low 11 FAN8621B Spindle Motor Driver The spindle motor driver has two operating modes : hard commutation in start-up and acceleration mode and soft commutation in steady state to reduce acoustic noise. Start-up and Acceleration To spin up the motor, open mode start-up clock must be fed to CNTL2 pin in range 20 ~ 200Hz depending on number of platter and motor RPM. This HIGH and OPEN signal commutates motor current in turn while back-EMF comparator checks back-EMF level. When the back-EMF detects motor position, then operating mode is changed from start-up mode to acceleration mode. Also internal commutation logic starts sensorless commutation. Speed Control Spindle motor speed is defined by system clock and RPMSEL (pin48) . For your reference, see table2 POR CNTL1 soft commutation CNTL2 CNTL3 VCM enable +0.7% TARGET RPM -0.7% start-up SPEED hard commutatio n INTERNAL READY READY user option 0.27sec Figure 2. Typical Control Sequence of the FAN8621B Speed and rotor position of spindle motor is measured by back-EMFs. Back-EMF comparator detects zero crossing point (ZCP) of unexcited phase back-EMF. The output frequency of comparator multiplied by 3 represents motor speed FG ( pin6). FG frequency is calculated as follows FG = motor RPM/60 × pole number/2 × phase number Pin Value System clock (CLK, pin8) Speed 5400 rpm 5MHz 7200 rpm 3600rpm 3.333MHz 4800rpm Table 2. RPM selection For example, 8 pole, three phase 5400 rpm motor, fFG = 5400 / 60 × 8 / 2 × 3 = 1080Hz 12 Rpm selection (RPMSEL, pin48) L H L H FAN8621B The spindle motor speed is controlled by SPLL which consists of Synchronous F/I converter , loop filter , and inner current control loop. F/I converter compares RPM reference time with 12 FG time one rotation of spindle for 8 pole motor. The time difference is converted into charge/discharge current source, and fed to loop filter consisting of external RC network. Loop filter acts ad speed controller and it’s output becomes spindle output current set point. If spindle motor speed is greater than target speed, switch s2 is turned on, thus decreasing output voltage of loop filter. Current limiting during start-up is achieved by sensing the voltage across the sense resistor connected PCS (pin 33). This limit the loop filer output. The output of loof filter is compared with internal 2.5V reference. If the difference is over 0.75V, the output is limited and scaled down. When the output of loof filter is 1.75V(2.5V-0.75V), the output of limitter is 0. The maximum output of limitter is 0.4V when the output of loof filter is over 3.25V. So spindle output current is linearly controlled by level shifted current set point driving high side vertical PNP TR of spindle output driver. Overall concept of SPM speed control is shown Figure3. U V W N VDD FG 6 speed discriminator & speed lock indicator CLK 8 counter/logic READY 47 i spll Freal Fref s1 39 s2 C39 i spll 1 48 33 I spindle RPMSEL R1 R33 C1a C1b Figure 3. Speed Control of SPM Indirect Rotor Position Sensing and Commutation The back-EMF comparator detects the instant at which the back-EMF in the unexcited phase cross as zero. The commutation timing and sequencing for driver outputs is determined by internal commutation logic based on back-EMF ZCP (zero crossing point). Commutation is initiated in advance of ZCP, 30° (electrical) for hard commutation and 1° for soft commutation, respectively. In BLDC motor with trapezoidal type back-EMF, phase current waveforms look like step wave, which generates audible noise. In soft commutation mode (CNTL2 pin45 is LOW), the two phase currents overlap with some current slope. This slope is determined by internal PWM pattern and external capacitor, CSOFT. The soft commutation using current slope of the motor reduce acoustic noise and voltage spark which is generated on the motor coil at the commutation. Spindle Output Driver Spindle Output driver contains vertical PNP TR for high side and NPN TR for low side. For one commutation period, PNP TR is controlled linearly by the difference between the current set point VCNT(pin1) and sensed current PCS (pin33), while NPN TR is fully turned on. This scheme provides low voltage drop in linear current control application. The total voltage drop is about 1.8V in 2A current rating. Maximum spindle current is defined as follows; 0.57V Ispindle ( max ) = -------------------------------------R33 + Rmetal Where Rmetal is internal metal resistance(typically 50mΩ). If R33 is 150mΩ, the maximum spindle current is 2A. Spindle Brake There are two braking modes; internal and external braking. Spindle is braked when CNTL1 (pin44) is LOW by turning all low side driver on. In case of power failure, brake power is supplied by charged capacitor connected CBRAKE (pin41). Gate signal for two external MOSFET is issued from BRAKE (pin40) with time delay, which is defined by internal resistor (2.8M) and external capacitor. 13 FAN8621B 18 41 C41 PVCC 2.8M VDD V 37 M40a 40 34 W 32 C40 M40b brake 33 R33 Figure 4. Brake Function Block Voice Coil Motor Driver VCM Current Set Point VCM current set point is defined by two PWM signals. External capacitor connected CFVCM (pin15) is charged and/or discharged depending on status of PWM signals. The voltage, level shifted by 4V, is filtered by an internal 2-nd order filter and converted into DC voltage, FILOUT (pin19) ranging from VCMREF4V+2V to VCMREF4V-2V. The cutoff frequency of the 2nd order filter is about 100KHz, so the PWM frequency must be grater than 100KHz. For more resolution of VCM current set point, the value of two internal current sources for PWMH and PWML is not equal. The weight is 64, so it is good that frequency of PWMH is different that of PWML. When PWM signal is LOW, CFVCM (pin15) voltage increases This voltage is limited by internal 4V reference and resistor, RFVCM. VDD VDD VCMREF4V R fvcm ipwml ipwmh =4K 20K PWMH 13 PWML 14 ipwml 80pF 20K 80pF 19 ipwmh 15 C15 Figure 5. Current Set Point with PWMs Sense Amplifier Current sense amplifier amplifies the differential voltage across the sense resistor which is in series with VCM coil. This amplified voltage is level shifted by VCMREF4V. The amplifier gain is set to 2 or 8 depending on GAINSEL. The output of the current sense amplifier is available at SENSEOUT( pin25). 14 FAN8621B VCM Current Loop Error Amplifier The inverting input of error amplifier is summing point of VCM current set point (FILOUT) and actual VCM current (SENSEOUT). The output of error amplifier is proportional to the dynamically compensated voltage difference between FILOUT and SENSEOUT. This output voltage is level shifted to VCMREF4V via connecting non-inverting input of error amplifier internally to VCMREF4V. The dynamic compensation is achieved by external RC network connected to ERRIN (pin28) and ERROUT (pin30 ) VCM Power Amplifier The VCM power amplifier is a linear H-bridge type power driver consist of two NPN TR and two vertical PNP TR to reduce voltage drop. Total voltage drop is 1.5V at 0.7A. The differential gain of power amplifier is 14. If open loop gain of power and error amplifier is very large, the overall DC gain of VCM driver is calculated as follow 1 R25 1 Gm = ----------- ⋅ -------------------------------------------------- ⋅ ---------R19 R20 + R metal ( VCM ) A VS where R20 is VCM current sense resistor and Avs is gain of sense amplifier. Rmetal(VCM) is internal metal resistance(typically 0.05ohm). If R25 is equal to R19, R20 = 1Ω, and Rmetal(VCM) = 0, then overall DC gain is determined by the gain of sense amplifier. For Example,GAINSEL is low, 1 = 1 --- = 0.125 Gm = ---------A VS 8 And if GAINSEL is high, then 1 1 Gm = ---------- = --- = 0.5 A VS 2 power amp 30 27 C30 VCMREF4V error amp R28 VCC R27 D27 9 28 C27 power amp C9 VCM 23 R19 gain 14 19 D20 sense amp R25 R20 38 25 20 gain 2,8 VCMREF4V Figure 6. Current Control of VCM 15 FAN8621B VCM Retract Power fail condition or when VCM retract command is issued on CNTL3 (pin46) LOW, retract circuit is activated. The retract current is limited by internal and external resistor connected RRET (pin24) and retract delay time is adjusted by external capacitor connected CRET (pin 17). The voltage on CRET2 (pin21) charged by spindle back-EMF serves as retract power. 22 37 D21 34 21 32 bandgap reference C21 I rct= 300 Iret 20 1.3V retract TSD por Riret I ret 3k 2.0V 27 I cret 12u 17 C17 24 R24 Figure 7. Retract Function Block Retract delay time and maximum retract current is defined as follows; 1.25 T retdly = C17 ⋅ ----------I cret 2.0 I rct ( max ) = 300 ⋅ I ret = 300 ⋅ ------------------------3K + R24 Power Management Supplies Monitoring and Reference The voltage reference circuit generates precision 1.3V volt reference, other voltage and current reference. Precision low voltage monitor circuitry senses 5V, 12V supplies. These supplies are individually divided down by resistor divider and then compared with internal 2.5V reference to determine the set-point low voltage condition. Low voltage condition can be changed by adding external resistor on SENSE5 (pin4), SENSE12 (42). Power On Reset (POR) When low voltage is detected, POR (pin10) is lowered immediately and fed to external controller. The retract and braking sequence is started. If low voltage condition is removed, the POR becomes high with delay. This time delay is based on charging of the CDLY (pin11) capacitor with internal current source. 16 FAN8621B VCC VDD VDD icpor 25K 7K 42 10 4 9K 11K 2.5V 2.5V TSD 11 C11 Figure 8. Power Line Sensing and POR POR delay time is calculated by following formula 2.5 T dly = C11 ⋅ -----------I cpor Regulator An external passive element and two resistors generate regulated 3.3V supply suitable for external digital logic operating at the reduced voltage. Regulator output voltage is defined by resistor divider R3a V reg = 1.3 1 + ----------- R3b VDD bandgap reference 1.3V 7 Q7 3.3V R3a 3 R3b Figure 9. Regulator Output for Digital ASIC 17 FAN8621B Thermal Shut Down A TSD circuit is included to protect the chip from damaging during momentary shorts that might occur during prototyping and troubleshooting. The trip temperature is set to 150°C with 30°C hysteresis. A thermal fault starts retract and braking operation and also makes POR pin low. 18 FAN8621B Typical Application Circuits 5V 25K VDD 10 R3b C11 Q7 11 VCC R3a 5V 7 CDLY POR 3 VREF TSD 12V D5 5 ADJ 29 18 VDD VDD VCC V 7K M40a BRAKE 42 Bandgap Reference & Bias Power Management SENSE12 4 SENSE5 Retract 1.3V 11K 9K FG FG Generator 6 CSOFT 2 C2 Triangle Wave Generator clock External Brake U CBRAKE PVCC 38 CNTL2 CNTL3 U SPM bias enable 44 Three State Input Control 45 Commutation Sequencing & Spindle Control SPM output on start-up clock hard/soft 46 Brake VCM on/off Retract V W Real Speed 47 RPMSEL 48 i spll CCOMP CLK C1b 8 14 15 C15 12 GAINSEL VCMREF4V 16 32 SPM 39 ispll VCC error amp 12.7K 9 12.7K U V W VCM Gain Selection sense amp VCM+ SENSE gain 2,8 VCMREF4V RRET CRET2 21 R24 19 C17 ERRIN ERROUT 28 R19 30 12V 19 C30 D21 17 R28 C21 CRET FILOUT 24 23 PGND Intelligent Retract 43 VCM- 26 VCMREF4V Retract SENSEOUT 25 R25 12V C9 D20 gain 14 CFVCM GND D27 HALFVCC clock PWMs Decorder & 2nd orderFilter C39 VCM VCM+ 27 VCNT Counter & Timing Control R33 22 power amp VCMREF4V 12V PVCC R20 13 PWML 34 33 VCM H-bridge Power Driver power amp PWMH 37 PCS R1 C1a 36 SUBGND 35 pre amp Current Limiting Speed Discriminator & Speed Lock Indicator Speed Reference 1 12V SUBGND 31 VDD FG READY W M40b N CNTL1 C40 41 C41 U V W N SPM Three Phase Power Driver Back-EMF Processing & Zero Cross Detector 40 SENSE 20 R27 C27 FAN8621B Parts List Part NO. Value Type R1 280K 1/8W R3A 15K 1/8W R3B 10K 1/8W R19 6K 1/8W R20 1 1/2W R24 2.2K 1/8W R25 4K 1/8W R27 30 1/4W R28 2.2K 1/4W R33 0.33 1W C1A 1µ ELECTROLYTIC, 6V C1B 0.22µ CERAMIC, 6V C2 27n CERAMIC, 6V C11 0.047µ CERAMIC, 16V C15 0.68n CERAMIC, 10V C17 1µ ELECTROLYTIC, 16V C21 2.2µ ELECTROLYTIC,16V C30 33n CERAMIC,16V C39 0.1µ CERAMIC,16V C40 0.47µ ELECTROLYTIC,16V C41 2.2µ ELECTROLYTIC,16V Q7 KSH29 D-PACK M40A SSD2003 8SOP M40B SSD2003 8SOP D5 RB4110 SOT23 D20 RB4110 SOT23 D21 RB4110 SOT23 D27 RB4110 SOT23 20 FAN8621B DISCLAIMER FAIRCHILD SEMICONDUCTOR RESERVES THE RIGHT TO MAKE CHANGES WITHOUT FURTHER NOTICE TO ANY PRODUCTS HEREIN TO IMPROVE RELIABILITY, FUNCTION OR DESIGN. FAIRCHILD DOES NOT ASSUME ANY LIABILITY ARISING OUT OF THE APPLICATION OR USE OF ANY PRODUCT OR CIRCUIT DESCRIBED HEREIN; NEITHER DOES IT CONVEY ANY LICENSE UNDER ITS PATENT RIGHTS, NOR THE RIGHTS OF OTHERS. LIFE SUPPORT POLICY FAIRCHILD’S PRODUCTS ARE NOT AUTHORIZED FOR USE AS CRITICAL COMPONENTS IN LIFE SUPPORT DEVICES OR SYSTEMS WITHOUT THE EXPRESS WRITTEN APPROVAL OF THE PRESIDENT OF FAIRCHILD SEMICONDUCTOR INTERNATIONAL. As used herein: 1. Life support devices or systems are devices or systems which, (a) are intended for surgical implant into the body, or (b) support or sustain life, and (c) whose failure to perform when properly used in accordance with instructions for use provided in the labeling, can be reasonably expected to result in a significant injury of the user. 2. A critical component in any component of a life support device or system whose failure to perform can be reasonably expected to cause the failure of the life support device or system, or to affect its safety or effectiveness. www.fairchildsemi.com 12/1/00 0.0m 001 Stock#DSxxxxxxxx 2000 Fairchild Semiconductor International