AN1139 STMicroelectronics, AN1139 Datasheet - Page 38

• Manufacturer Part Number: AN1139
• Description: L6254 - L6268 - L6269 12V DISK DRIVE POWER COMBO IC
• Manufacturer: STMicroelectronics

AN1139 APPLICATION NOTE
Figure 21. External BEMF Processing & Speed Control Configuration
6.2
In Figure #22 is depicted a typical application circuit. The external components are selected to work with a
5400Rpm Spindle motor with inductance Lm=1.2mH phase to phase and resistor Rm=5.3
The Voice Coil is assumed with an inductance Lm=1.5mH and a resistor Rm=13.3 .
The maximum Spindle Start-Up current is set as VCC / (Rm+2rdson+Rsense) and it is equal to 1.85A with
Reg#8.4.5 bits set to 1. The VCC is equal to 12V. The maximum Voice Coil current is set to be 1A.
Since high current is demanded through the Spindle and Voice Coil sense resistor, 1W power dissipation ca-
pacity is recommended.
If Spindle Linear current control loop is selected, the capacitor (3), attached to PWM/SLEW pin (#3) can be
avoided. If Spindle PWM current control loop is selected, the components, one resistor and one capacitor (4),
attached to SPIN_COMP pin (#44) can be avoided.
The layers that goes from SENSE_IN+ and SENSE_IN- pins to the Voice Coil sense resistor must be at equal
distance. A capacitor (1) connected to VCC and Ground is required in order to clamp possible spike due to the
current recirculation in the Spindle windings. Since the absolute maximum rating of the VCC (pin #13) and VDD
(pin #19) lines are respectively 14V and 6V, precautions need to be taken in order not to allow the voltage on
this pins to go above the limits. A recommended capacitor on VCC pin for a 5400Rpm, two platters application
is 22 F Tantalum type. This capacitor needs to be placed as closest as possible to the VCC pin (#13). Also an
under voltage on VCC or VDD can be very dangerous especially when one of the two voltages is in place. This
can happen for example during plug and unplug test of the drive power supply connector. It is indeed recom-
mended to use a protection circuit in order to better protect the Supply lines. A good layout by separating the
grounds will improve the noise immunity of the system.
38/64
Microprocessor
C O N T R O L L O O P
TYPICAL APPLICATION
P R O C E S S I N G
or DSP
S P E E D
B E M F
F L L _ F I L T E R P I N
I N D E X P I N
S Y S C L K
S D A T A
S D E N
F C O M
S C L K
P O R
P O W E R C O M B O
V O I C E C O I L
phase to phase.
S P I N D L E
M O T O R
M O T O R