SLFS040

– DECEMBER 1993

POST OFFICE BOX 655303

DALLAS, TEXAS 75265

12

PRINCIPLES OF OPERATION

Figure 3 shows a block diagram of the TLS2205 retract equivalent circuit (retract mode only).

Spindle Motor

VCMB

RETSET

Vbe

CVDD

VDD

Rrset1

1

Rsvcm

RRETRACT

(or shorted)

N

U

VW

Clamp

VCM

Cret

CRET

RETOUT

NOTE: Area within the dotted line is internal to the device

VCMA

Rrset2

Rlsd

Figure 3. Retract Equivalent Circuit

spindle-driver system

The spindle-driver system is capable of

1-A output current and has a total drain-to-source on-state resistance

(2

Soft switching on the output drivers eliminates the need for external snubbers or flyback

diodes. An internal voltage clamp circuit helps protect against flyback voltages, while internal Schottky diodes

provide a low-loss power path for the VCM retract function. Internal logic and analog detection circuitry provide

complete sequencing of the power outputs in all run modes. Support for unipolar operation is provided by

disabling the spindle high-side drivers and pulling the motor center tap to 5 V using an external pnp or PMOS

transistor. CTDRV is used to control the base of the transistor during unipolar operation and is open otherwise.

During a fault condition, the spindle-motor drivers are disabled.