1999 June 10

15

Philips Semiconductors

Preliminary specification

5 V spindle & VCM driver combo

TDA5345HT

The digital control block ignores any crossing while the Blank1 timer is counting. This means that the zero-crossing

The WatchDog timer makes sure that the motor is running forward. If the motor is going backwards, the BEMF voltage

Therefore, if the WatchDog timer expires before a zero-crossing occurs, the motor is assumed to be turning backwards.

the WatchDog time. Therefore, the WatchDog must be set to a time that is greater than the fly-back pulse duration

measured when the motor is standing still.

zero-crossing all extra zero-crossings are ignored during the Blank2 time. This allows the coil voltage to ring slightly

without causing a commutation advance.To make the chip smaller, Blank1 and Blank2 have the same value: Blank.

If the motor is not spinning, no BEMF zero-crossing will occur. The StartUp timer detects this if it expires before the true

The Commutation Delay Limiter (ComDeLim) allows to control the maximum commutation delay time. This commutation

delay time is equal to half the measured delay between 2 zero crossings

fly-back pulse

Commutation

true zero crossing

WatchDog

Blank1

Blank2

Commutation

StartUp

Fig.8 A typical motor commutation diagram

CENTER TAP

delay

Commutation

false zero crossings

SpinMotA

SpinMotB

SpinMotC

ZOOM