TDA5345HT datasheet(23/44 Pages) PHILIPS

23 / 44 page

1999 June 10

Philips Semiconductors

Preliminary speciﬁcation

5 V spindle & VCM driver combo

TDA5345HT

During the VCM brake, VCM power transistors N- & N+ are switched fully On while transistors P- & P+ are switched off.

During the soft retract step, N- transistor is switched off while the retract PMOS brings some current to the VCM. The

control loop is drawn in figure 14 (the voltage on VcmMinus is regulated).

Fig.15 Power transistors structure during a retract phase

(ext.)

VDD=5V

GND=0V

SpinRectBemf

Vcm-

Vcm+

Off

Retract PMOS

PA (resp. PB, PC) is switched On

NA (resp. NB, NC) is switched On

The back-EMF is synchronously rectified

when MotA (resp. MotB, MotC) is above SpinRectBemf

when MotA (resp. MotB, MotC) is below GND

by the spindle power transistors:

(ext.)

MotA

MotB

MotC

Isolation switch, used in reverse mode

(ext.)

P-

P+

N-

N+

VCM

Rsense

Fig.16 VCM retract circuitry

RetPmosDrain

SpinRectBemf

retract amplifier

(2)

(62)

Retract PMOS

Internal voltage reference

=> 125 mV in slow retract

=> 250mV in full power.

Programmable

voltage divider

VCM

(11)

VcmPlus

Rsense

(ext.)

VcmMinus

(6)

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