1999 June 10

14

Philips Semiconductors

Preliminary specification

5 V spindle & VCM driver combo

TDA5345HT

Commutation control

The spindle block contains both the low-side and high-side drivers configured as a H bridge for a three phase DC

brushless, sensorless motor. In each of the six possible states, two outputs are active, one sourcing current and one

sinking current. The third output presents a high impedance to the motor which enables measurement of the BEMF in

the corresponding motor coil. The back-EMF comparator output (available on pin SpinDigOut) is processed by the

commutation logic circuit to calculate the correct time for the next commutation, which will change the output state.

The commutation block measures then the time between 2 consecutive zero-crossings and determines the actual

commutation time and the next motor coils state. All the following situations must be taken into account:

=> Start up, No start, Backwards spin, Run and Manual commutation.

The commutation logic keeps the motor spinning by commutating the motor each time a zero-crossing is detected. The

delay between the zero-crossing and the actual output driver change is either internally calculated or programmable via

the serial port (useful at start-up: no delay has been measured!).

The internal commutation clock can be monitored on pin SpinDigOut (44). The falling edges are the relevant

informations: they are caused by the zero-crossings. If preferred, SpinDigOut can be set to become the back-EMF

comparator output, to check if the spindle is already spinning at power up for instance. If the spindle outputs are floating,

don’t forget to bias them, using the “BiasCT” bit, before considering the BemfCompOut value.

Fig.6 and Fig.7 show typical motor commutation timing diagrams.

SpinMotA

SpinMotB

SpinMotC

Commutation

BemfCompOut

L

L

F

HH

F

H

F

LL

F

H

F

HH

F

L

L

Fig.7 Input commutations to output drivers

Clock

Zero-crossing

State Code

0

1

2

3

4

5