SLFS040

– DECEMBER 1993

POST OFFICE BOX 655303

DALLAS, TEXAS 75265

16

PRINCIPLES OF OPERATION

spindle-current control

Spindle-current control is accomplished by regulating the current through the external sense resistor, Rsspn,

via the spindle low-side drivers (LSD). Figure 6 illustrates the arrangement for the spindle-current control

(port C, bit 5) during the start mode (SPNMODE = 1) and the run mode (SPNMODE = 0). During startup

(SPNMODE = 1), the 8-bit DAC is used to command the spindle start current. Upon switching to the run mode

(SPNMODE = 0), the 8-bit DAC is used to control the VCM and the spindle motor is switched into closed-loop

operation (see Figure 6). The transconductance function is:

Note:

Rsspn is typically 0.2

Maximum spindle current is load dependent. The following equation should be used as a guideline to determine

maximum spindle current:

where:

Rtotal = Rsspn + 2

_

+

8-B

D/A

8

To VCM

(see Functional

Block Diagram)

(0

– 2 V)

S

2

HSD

SPNVCC

EN

Rspn

Cspn2

R4

Rsspn

SPNSNSR2

SPNCOMP

LSD

NOTE: For startup mode (SPNMODE = 1), S = closed

For run mode (SPNMODE = 0), S = open

Area within the dotted line is internal to the device

VCC

U, V, or W

_

+

R2

Cspn1

SPNMODE

Vref

R3

R1

SPNSNSR1

SPNSW

Figure 6. Spindle-Current Control