TDA5345HT 데이터 시트보기 (PDF) - Philips Electronics

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TDA5345HT

5 V spindle & VCM driver combo

Philips Electronics 

Philips Semiconductors

5 V spindle & VCM driver combo

Preliminary specification

TDA5345HT

SpinMotA

SpinMotB

SpinMotC

Blank1

CENTER TAP

WatchDog

Blank2

StartUp

ZOOM

Commutation

delay

Commutation

Zc1

Zc2

fly-back pulse

false zero crossings

Zc3

Commutation

true zero crossing

Fig.8 A typical motor commutation diagram

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

caused by the fly-back pulse leading edge (ZC1) is not seen by the commutation block.

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

will be inverted and the second crossing (ZC2) of the inductive pulse will not occur until the actual BEMF zero crossing.

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

The commutation is advanced one step to correct this condition. The second inductive zero-cross (ZC2) must occur within

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.

The Blank2 timer starts counting as soon as the second zero-cross (ZC2) occurs. After the second inductive

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

zero-crossing (ZC3) has occurred. It will advance the commutation one step if this happens.

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 (∆Zcmeasured). ComDeLim value should be

1999 June 10

15

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