L8150

Operating description

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2b) The desired direction is not equal to the detected direction so that rectangular mode is

used, the current limiter control method is forcing all the phases in high impedance state.

In any case, current control method is updated every PWM cycle period.

The amplitude of the voltage waveform applied to the motor windings allows the control to

modulate the rotation speed; this is achieved through an 8-bit analog-to-digital converter

(ADC) transforming the output voltage of the control amplifier (INTAMP) into an 8-bit digital

word that is used to scale the voltage waveform applied to the motor windings. A digital

multiplier, whose inputs are the 8-bit samples of the voltage waveform (that is the output of

the 8-bit ADC), gives an 8-bit word that represents the voltage to be applied to the motor

winding.

Furthermore, control signal actuation is performed through a fixed frequency digital PWM

converter, that is converting the 8-bit word coming from the comparator into a digital signal,

whose duty cycle is proportional to the resulting voltage to be applied to the motor windings.

The period of the PWM output signal is:

resulting in a frequency that is 19.2 kHz in the typical case.

Motor position is detected through a set of three Hall sensor, whose output is differentially

fed into the device; after processing the signal by means of a comparator (whose

characteristics are explained in the Electrical Characteristics section) the signal is

furtherly filtered through a digital circuit to prevent noise from causing any device

malfunctioning.

The filtering circuit processes signals coming from Hall sensors comparators (HallU, HallV,

HallW) and generates a set of three internal signals used inside the digital part of the circuit

(PosFil).

Figure 11.

Filtering circuit

In order to simplify the explanation of the filtering circuit a signal Pos will be defined that can

assume 7 different values according to the following table:

The filtering action takes place according to the following picture (Fig. 7).

Table 22.

7 different values of the signal Pos

HallU

11

100

00

HallV

00

111

00

HallW

10

001

10

Pos

p1p2p3p4p5p6pErr

HallU

HallV

HallW

PosFil

Hall sensor

filtering

block

From input

comparator

To control

logic

3