1999 June 10

22

Philips Semiconductors

Preliminary specification

5 V spindle & VCM driver combo

TDA5345HT

(13)

Where:

(14)

and if you set:

(15)

you get:

(16)

(17)

VCM ramp unload sequence :

The VCM ramp unload sequence can be ordered by either the serial interface or by internal emergency procedures:

power down or temperature shut down. It will not start if VcmSleep bit is ‘1’, because the actuator is supposed to be

on the ramp already.

Three different states are programmable : first a VCM brake, second a VCM slow retract and then a VCM full power

retract.

In all cases, the spindle isolation switch is cut off. If the power transistors are still supplied, the VCM current will come

from the power supply, through the isolation switch parasitic diode. If the power transistors are no more supplied, the

VCM current will come from the spindle itself. It is used as a generator, thanks to its back-EMF.

When the sequence is initiated by a Power down detection, PorN signal will not go up until the end of the sequence.

Figure 14 shows the link created between the spindle and the VCM power structures to transfer the spindle energy to

the actuator :

VcmBemf

2

V

( cmPlus VcmSenseInM )

R1

R2

--------

R

Sense

I

VCM

×

×





+

–





×

VcmRef

+

=

V

VCM

VcmPlus

VcmSenseInM

–

(

)

–

=

R1

R2

--------

R

Sense

×

R

VCM

=

VcmBemf

2

–

V

VCM

R

VCM

I

VCM

×

–

(

)

×

=

VcmRef

+

VcmBemf

2

–

e

×

=

VcmRef

+