E-L8150 STMICROELECTRONICS [STMicroelectronics], E-L8150 Datasheet - Page 21

• Manufacturer Part Number: E-L8150
• Description: Brushless motor predriver
• Manufacturer: STMICROELECTRONICS [STMicroelectronics]

L8150
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:
Table 22.
The filtering action takes place according to the following picture (Fig. 7).
HallU
HallV
HallW
Pos
From input
comparator
1
0
1
p1
7 different values of the signal Pos
1
0
0
p2
HallU
HallV
HallW
1
1
0
p3
T
Hall sensor
PWM
filtering
block
= 512 Tck
0
1
0
p4
PosFil
0
1
1
p5
3
To control
logic
Operating description
0
0
1
p6
0
0
0
pErr
21/37