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FAN8621B
12V Spindle Motor and Voice Coil Motor Driver IC
Features
General
* * * * 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
Description
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.
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
* Hard disk drive(HDD)
Ordering Information
Device FAN8621B Package 48-QFPH-1414 Operating Temp. 0 ~ 70C
Rev. 1.0.0 May. 2000.
(c)2000 Fairchild Semiconductor International
1
FAN8621B
Pin Assignments
B
2
FAN8621B
Pin Definitions
Pin Number 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 29 30 31 32 Pin Name VCNT CSOFT ADJ SENSE5 VDD FG VREF CLK HALFVCC POR CDLY GAINSEL PWMH PWML CFVCM VCMREF4V CRET VCC FILOUT SENSE CRET2 PVCC VCMRRET SENSEOUT PGND VCM+ ERRIN VDD ERROUT SUBGND W IO A A A A P O P I P O A I I I A P A P A A A P A A A P A A P A P A Pin Function Description Speed controller output. Range 3.8V to 0.5V Capacitor for soft commutation Adjust external regulator voltage (VREF) 5V power line sensing 5V power line Frequency generation for spindle rotation speed. Typically 1.08KHz (5400RPM) Regulator voltage output. This voltage is controlled by pin 3 voltage System clock. Digital clock input as a time reference 1/2 VCC Power on reset. H : normal, L: power fail Define POR delay time Sense amplifier gain selection. H : High gain (8), L : Low gain (2) Coarse PWM input for VCM set point Fine PWM input for VCM set point Output of PWM inputs to voltage converter 4V reference output for VCM Define retract delay time. 12V power line Filtered output of PWM inputs. This voltage define VCM set point Non-inverting input of differential amplifier for VCM current sensing Power for retract when power down 12V power line for VCM Negative output terminal of VCM power amplifier Adjust maximum retract current Output of differential amplifier for VCM current sensing Ground for VCM positive output terminal of VCM power amplifier Inverting input of VCM error amplifier 5V power line Output of VCM error amplifier Ground for spindle motor Spindle W phase output
3
FAN8621B
Pin Definitions (Continued)
Pin Number 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 Pin Name PCS V SUBGND N U PVCC CCOMP BRAKE CBRAKE SENSE12 GND CNTL1 CNTL2 CNTL3 READY RPMSEL IO A A P A A P A A A A P I I I O I Pin Function Description Spindle current sensing. Spindle V phase output Ground for spindle Spindle N phase output Spindle U phase output 12V power line for spindle Current controller output. This Voltage define spindle output current Gating signal for external brake Charged back-EMF to supply brake power when power down 12V power line sensing Ground Control input for spindle . H: spindle enable, Z: Spindle bias enable, L: brake Start-up clock and soft commutation. H: Start-up clock , L : soft commutation. Control input for VCM. H: VCM enable, Z : VCM disable, L: retract Speed lock indicator when speed is within 0.7% speed error range. H : speed locked, L: unlocked Target spindle speed selection. L : 5400 rpm, H: 7200 rpm with 5MHz Clock
4
FAN8621B
Internal Block Diagram
CDLY
11 VCC
25K
POR
10 TSD
VREF
7
ADJ
3
VDD VDD VCC
5 29 18
VDD
7K
SENSE12 SENSE5
42 4
9K 11K
Power Management
Bandgap Reference & Bias
1.3V
Retract
External Brake
40 41 U V W N 38
BRAKE CBRAKE
U
FG
6
FG Generator
CSOFT
2
clock
Triangle Wave Generator
Back-EMF Processing & Zero Cross Detector
SPM Three Phase Power Driver
PVCC
36 37 Commutation Sequencing & Spindle Control 34 32 35 pre amp 31
N U V W SUBGND SUBGND CCOMP PCS PVCC VCM+
SPM bias enable
CNTL1 CNTL2 CNTL3
44 45 46
VCM on/off Retract
Three State Input Control
SPM output on start-up clock hard/soft Brake
VDD
FG
Real Speed
i spll
READY RPMSEL
47
48
Speed Discriminator & Speed Lock Indicator
Current Limiting
39 33 VCM H-bridge Power Driver VCMREF4V power amp VCC error amp
clock
22
Speed Reference
i spll
VCNT
27
1
CLK
8
Counter & Timing Control
9 power amp gain 14 26
HALFVCC
PWMH PWML CFVCM GAINSEL
13 14 15 12
PWMs Decorder & 2nd orderFilter
23
VCMPGND
U
V
W
Retract
VCMREF4V sense amp gain 2,8
VCM Gain Selection
Intelligent Retract
VCM+ SENSE
20
SENSE
VCMREF4V
16
VCMREF4V
43
21
24
17
19
28
30
25
GND
CRET2 RRET CRET FILOUT ERRIN
ERROUT
SENSEOUT
5
FAN8621B
Absolute Maximum Ratings(Ta = 25C)
Parameter Supply voltage (signal) Supply voltage (signal) Supply voltage (power) Storage Temperature Power dissipation Maximum Junction Temperature Operating Ambient Temperature Symbol VDD VCC PVCC TSTG PD TJ TAMB Value 6.0 15.0 15.0 -55 ~ 125 3.0
note
Unit V V V C W C C
150 0 ~ 70
NOTE: 1. When mounted on 50mm x 50mm x 1mm PCB (Phenolic resin material) 2. Power dissipation is reduced 16mV / C for using above Ta=25C. 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 = 25C)
Parameter Supply voltage (signal) Supply voltage (signal) Supply voltage (power) Symbol VDD Vcc PVCC Min. 4.5 10.8 10.8 Typ. 5.0 12.0 12.0 Max. 5.5 13.2 13.2 Unit V V V
6
FAN8621B
Electrical Characteristics
(Ta=25C, unless otherwise specified) Parameter POWER SUPPLIES SUPPLY CURRENT VDD Line supply current1 VDD Line supply current2 VDD Line supply current3 VDD Line supply current4 VCC Line supply current1 VCC Line supply current2 VCC Line supply current3 VCC Line supply current4 SUPPLY MONITOR Threshold voltage1 for VCC Threshold voltage2 for VCC Hysteresis on VCCcomparator Threshold voltage1 for VDD Threshold voltage2 for VDD Hysteresis on V comparator Charging current for POR cap POR threshold voltage Output high voltage Output low voltage VTH12A VTH12B VHYS12 VTH5A VTH5B VHYS5 ICPOR VTHPOR VPORH VPORL VCC = 12V, VDD= 5V, POR output current is 1mA VCC = 12V, VDD= 5V, POR output current is 1mA CNTL1=CNTL2=CNTL3=sweep CNTL1=CNTL2=CNTL3=sweep CNTL1=CNTL2=CNTL3=sweep CNTL1=CNTL2=CNTL3=sweep VCC=sweep,VDD=5V VCC=sweep,VDD=5V VCC=sweep,VDD=5V VCC=12V,VDD=sweep VCC=12V,VDD=sweep VCC=12V,VDD=sweep 9.05 8.75 0.15 3.45 3.30 0.08 -18.0 1.1 4.5 0 9.40 9.10 0.3 3.90 3.75 0.15 -14 1.3 9.75 9.45 0.45 4.15 4.00 0.23 -10 1.5 Vdd 0.5 V V V V V V A V V V IDD1 IDD2 IDD3 IDD4 ICC1 ICC2 ICC3 ICC4 CNTL1=L,CNTL2=CNTL3=Z (brake) CNTL1= CNTL2 =CNTL3=Z (SPM bias enable) CNTL1=CNTL3=H,CNTL2=Z (SPM,VCM enable) CNTL1=CNTL2=Z,CNTL3= L (retract) CNTL1=L,CNTL2=CNTL3=Z (brake) CNTL1= CNTL2 =CNTL3=Z (SPM bias enable) CNTL1=CNTL3=H,CNTL2=Z (SPM,VCM enable) CNTL1=CNTL2=Z,CNTL3=L (retract) 8025 25 25 2 4 10 12 100 35 35 35 7 9 20 19 120 45 45 45 12 15 60 25 mA mA mA mA mA mA mA mA Symbol Condition Min. Typ. Max. Unit
POWER ON RESET GENERATOR
CONTROL INPUTs(CNTL1,CNTL2,CNTL3) Control input low voltage Control input high voltage Control input low current Control input high current VCTL VCTH ICTl ICTH 0.8 1.85 -290 55 1.3 2.3 -200 110 1.7 2.75 -110 190 V V A A
7
FAN8621B
Electrical Characteristics (Contnued)
(Ta=25C, unless otherwise specified) Parameter SPINDLE MOTOR (SPM) FG FREQUENCY GENERATOR FG frequency FG duty FG output high voltage FG output low voltage READY SIGNAL GENERATION READY high output READY low output U Saturation voltage upper VSaturation voltage upper W Saturation voltage upper U Saturation voltage lower V Saturation voltage lower W Saturation voltage lower RPMSELECT INPUT RPMSEL threshold voltage RPMSEL input high current RPMSEL input low current SPEED CONTROLLER Speed controller high voltage Speed controller low voltage High voltage of linear range Low voltage of linear range F/I converter charge current F/I converter discharge current Transeconductance gain of SPM CURRENT LIMITTER Limit voltage of current amp Limit voltage of current amp Equivalent output resistance EXTERNAL REGULATOR Regulator output voltage Regulator line regulation Regulator load regulation VREG
RLINE VCNTH
Symbol
Condition
Min.
Typ.
Max.
Unit
FFG DFG VFGH VFGL
CLK=5MHz,RPMSEL=L (5400 RPM) FFG = 1.08KHz FG output current is 1mA FG output current is 1mA CNTL1=H,within 0.7% motor speed error, READY output current is 1mA IU=1A IV=1A IW=1A IU=1A IV=1A IW=1A RPCS=0.33
0.97 45 4.5 -
1.08 50 -
1.18 50 VDD 0.5
KHz % V V
VRDH VRDL VSUU VSVU VSWU VSUL VSVL VSWL VRPH IRPHI IRPLO
4.5 0.2 0.2 0.2 0.2 0.2 0.2 1.1 60 -5 3.5 3.15 1.15 -70 40 0.6
0.6 0.6 0.6 0.4 0.4 0.4 1.5 91 0 3.8 3.5 1.5 -50 52 0.8
VDD 0.5 1.0 1.0 1.0 0.8 0.8 0.8 1.7 110 5 4.2 0.5 3.85 1.85 -40 70 1.0
V V V V V V V V V A A V V V V A A -
SINDLE OUTPUT SATURATION VOLTAGE
VCNTL VLIMITH VLIMITL ISPLLC ISPLLD GMSPM
VLIMIT1 VLIMIT2 RCC
RPCS = 0.33 RPCS = 0.33 VADJ(pin3) = 1.3V IO= 500mA
-
0.57 0 20 3.3 -
2.0 2.0
V V K V % %
RLOAD
8
FAN8621B
Electrical Characteristics (Contnued)
(Ta=25C, unless otherwise specified) Parameter SPINDLE MOTOR (Continued) BRAKE Cbrake output voltage Brake output high voltage Brake output low voltage SOFT COMMUTATION Soft commutation high voltage Soft commutation low voltage Discharging current Charging current DRIVE OUTPUTS (U,V,W) Total voltage Drop Leakage current PWM INPUTS PWMH/PWML high input voltage PWMH/PWML low input voltage PWMH charge/discharge current PWML charge/discharge current PWM current ratio Internal resister VCN PWM FILTER Maximum phase shift Cut-off frequency Attenuation at 1MHz Filter output voltage1 Filter output voltage2 Filter output voltage3 VCM REFERENCE VCM reference voltage 4V VCM reference voltage 1/2 VCC VREF4 VREF6 CNTL3 = 5V, VREF4V output current=1mA HALFVCC output current =1A 3.8 5.9 4 6.0 4.2 6.1 V V DF FCO FITER VCVCM1 VCVCM2 VCVCM3 Measure at 500Hz, CCFVCM = 1nF PWMH=PWML=0% PWMH=PWML=50% PWMH=PWML=100% 5.6 3.8 1.6 100 70 6.00 4.0 2 -2 6.40 4.2 2.4 deg KHz dB V V V VPWMH VPWML IPWMH/IPWML 2.8 650 10 63 670 10.5 64 3 2.2 690 11 65 k V V A A VDROPS ILEAKS IMOTOR = 1A -10 0 1.8 10 V A VSOFTH VSOFTL ISOFTC ISOFTD 3.1 1.4 30 -60 1.7 45 -45 3.7 2.0 60 -30 V V A A VBC VBH VBL 11 11 11.3 - 11.8 - 0.5 V V V Symbol Condition Min. Typ. Max. Unit
VOICE COIL MOTOR CIRCUIT(VCM)
IPWMH IPWML
IRATIO RFVCM
9
FAN8621B
Electrical Characteristics (Contnued)
(Ta=25C, unless otherwise specified) Parameter SENSE AMPLIFIER Amp high output voltage Amp low output voltage Input offset voltage Short circuit current Unity gain bandwidth Voltage gain 1 Voltage gain 2 ERROR AMPLIFIER Amp high output voltage Amp low output voltage Input offset voltage Open loop gain Unity gain bandwidth Short circuit current POWER AMPLIFIER Output high voltage Output low voltage Input offset voltage Gain Unity gain bandwidth Total voltage Drop Leakage current VCM AMP TOTAL VCM offset current VCM transconductance low gain VCM transconductance high gain RETRACT FUNCTION Min operating voltage of CRET2 VCRET2 Cret charge current Max. retract sink current Retract reference voltage Retract current limit resister Leakage current of output TR Sink saturation voltage THERMAL SHUT DOWN Operating temperature Thermal hystereis TTSD THYS 135 20 150 30 165 40 C C ICRET IRCT VRET RIRET ILRET VRTSAT 2.0 -70 0.75 -10 -85 125 0.9 3 0 0.4 -100 1.05 10 0.7 V A mA V K A V VVCMOS GMVH GMVL PWMH=PWML=50% Duty GAINSEL = H,sense resister is 1 GAINSEL = L,sense resister is 1 -20 0.05 0.35 0 0.12 0.45 20 0.14 0.55 mA A/V A/V VPOH VPOL VOSP APO BGP VDROPV ILEAKV when VCM current is 0.7A 11.5 -15 21.2 -20 0 22 2 0 0.5 15 23.8 1.5 20 V V mV dB MHz V A VEOH VEOL VOSE AVE BGE ISSE 10.8 -15 8 0 80 2 1.2 15 V V mV dB MHz mA VSOH VSOL VOSS ISSC BGS AVS1 AVS2 GAINSEL : L GAINSEL : H 10.8 -15 10 0 2 18 6 1.2 15 V V mV mA MHz dB dB Symbol Condition Min. Typ. Max. Unit
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 CNTL1 CNTL2 CNTL3 RPMSEL READY
Power Management Interface
DIGITAL ASIC
SPM
FG PWMH PWML GAINSEL VCMREF4V
VCM
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 Signals CNTL1 CNTL2 CNTL3 GAINSEL SPM Brake Commutation Start Clock VCM Retract Start-up hold Sense Amp gain
H enable(1) disable hard high(2) enable disable normal 2
Z bias enable disable Hard low(2) disable disable normal 2
L disable enable soft disable enable hold(3) 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 CNTL2 CNTL3
TARGET RPM -0.7%
soft commutation VCM enable
+0.7%
SPEED
start-up 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 x pole number/2 x phase number
Pin Value Speed 5400 rpm 7200 rpm 3600rpm 4800rpm
System clock (CLK, pin8) 5MHz 3.333MHz Table 2. RPM selection
Rpm selection (RPMSEL, pin48) L H L H
For example, 8 pole, three phase 5400 rpm motor, fFG = 5400 / 60 x 8 / 2 x 3 = 1080Hz
12
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
Freal
speed discriminator & speed lock indicator
i spll s1
39
READY FG
47 6
s2 i spll
C39
Fref
CLK 8 counter/logic 48 RPMSEL
1
33
I spindle
R1 R33 C1b C1a
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 50m). If R33 is 150m, 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 40 M40a
37 34
W 32 C40 brake M40b
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
80pF
20K PWMH PWML 13 14
20K 80pF
19
ipwml
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 + Rmetal ( 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 = 1, and Rmetal(VCM) = 0, then overall DC gain is determined by the gain of sense amplifier. For Example,GAINSEL is low,
1 -Gm = ---------- = 1 = 0.125 A VS 8
And if GAINSEL is high, then
1 1 Gm = ---------- = -- = 0.5 A VS 2
30 C30 R28 28 power amp R19 19 sense amp 25 gain 2,8 VCMREF4V error amp
power amp 27 VCC D27 9 C27 C9 R27
VCM
23 gain 14 38 20 R20 D20
R25
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.
37 34 32 bandgap reference
22 D21 21 C21
I rct=
300 Iret
20
1.3V
retract TSD por
Riret
3k
I ret
2.0V 27
I cret
12u
17
24
C17
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 42 4 9K 11K 2.5V
2.5V
7K
10
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 1.3V 7 Q7 3.3V R3a 3 R3b
bandgap reference
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 150C with 30C hysteresis. A thermal fault starts retract and braking operation and also makes POR pin low.
18
FAN8621B
Typical Application Circuits
5V
R3b R3a
Q7 D5
5V
C11 11 VCC
25K
12V
5 29 18
10 CDLY POR TSD
7 VREF ADJ
3
VDD
7K
VDD VDD VCC V BRAKE
M40a
42
SENSE12
4
SENSE5
9K 11K
Power Management
Bandgap Reference & Bias 1.3V
Retract
External Brake
40 CBRAKE C40 41 C41
M40b
W
U
FG
6
FG Generator
CSOFT 2 C2
clock
Triangle Wave Generator
Back-EMF Processing & Zero Cross Detector
SPM Three Phase Power Driver
U V W N PVCC
38
12V
N
36 37 34 32
CNTL1 CNTL2 CNTL3
SPM bias enable
U
Commutation Sequencing & Spindle Control
44 45 46
VCM on/off Three State Input Control
SPM output on start-up clock hard/soft Brake
V W
Retract
VDD
SUBGND 31 SUBGND 35
SPM
FG
READY
47
Real Speed Speed Discriminator & Speed Lock Indicator
i spll
Current Limiting
pre amp
CCOMP PCS
39 33
RPMSEL
48
Speed Reference 1
ispll
VCMREF4V
VCM H-bridge Power Driver power amp
PVCC 22 VCM+ 27 VCC
12V
R33
C39
VCNT error amp
clock
VCM
D27
R1 C1a C1b
CLK
8
Counter & Timing Control
12.7K
HALFVCC
9
12.7K
12V
C9 D20
R27 C27
PWMH
13
power amp
PWMs Decorder & 2nd orderFilter
VCM23 R20
PWML
14 15 C15 12
U
V
W
Retract
gain 14 PGND VCMREF4V sense amp gain 2,8 26
CFVCM VCM Gain Selection
GAINSEL VCMREF4V
16
Intelligent Retract
VCM+ SENSE
SENSE 20
VCMREF4V
GND 43
CRET2 21 C21
RRET 24 D21
CRET FILOUT 17 R24 C17 19
ERRIN ERROUT 28 R19 30
SENSEOUT 25 R25
R28
C30
12V
19
FAN8621B
Parts List
Part NO. R1 R3A R3B R19 R20 R24 R25 R27 R28 R33 C1A C1B C2 C11 C15 C17 C21 C30 C39 C40 C41 Q7 M40A M40B D5 D20 D21 D27 Value 280K 15K 10K 6K 1 2.2K 4K 30 2.2K 0.33 1 0.22 27n 0.047 0.68n 1 2.2 33n 0.1 0.47 2.2 KSH29 SSD2003 SSD2003 RB4110 RB4110 RB4110 RB4110 Type 1/8W 1/8W 1/8W 1/8W 1/2W 1/8W 1/8W 1/4W 1/4W 1W ELECTROLYTIC, 6V CERAMIC, 6V CERAMIC, 6V CERAMIC, 16V CERAMIC, 10V ELECTROLYTIC, 16V ELECTROLYTIC,16V CERAMIC,16V CERAMIC,16V ELECTROLYTIC,16V ELECTROLYTIC,16V D-PACK 8SOP 8SOP SOT23 SOT23 SOT23 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.
www.fairchildsemi.com 12/1/00 0.0m 001 Stock#DSxxxxxxxx 2000 Fairchild Semiconductor International
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.

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