AN2281 datasheet(6/38 Pages) STMICROELECTRONICS

6 / 38 page

Implementation on the ST7LITE35 microcontroller

AN2281

6/38

Implementation on the ST7LITE35 microcontroller

The algorithm presented in the previous paragraph has been implemented on the

ST7FLITE35 microcontroller. Although they belong a family of low-cost ST microcontrollers,

ST7FLITE3x devices nevertheless have all the necessary features to be able to drive a

PMAC motor using one Hall sensor.

●

The Lite Timer has been used to measure the period (or better the semi-period) of the

Hall sensor signal and the 12-bit autoreload Timer with its 4 PWM outputs has been

used to generate the three voltage phases.

●

The internal RC oscillator with 1% tolerance allows you to further reduce the cost and

the size of the overall system and avoid PCB layout optimization issues related to the

presence of external oscillators.

3.1

ST7LITE3x 12-bit autoreload timer (ART) in PWM mode

3.1.1

Block diagram and functional description

The 12-bit ART is based on one or two free-running 12-bit upcounters with an input capture

The PWM mode of the dual 12-bit autoreload timer allows up to four Pulse Width Modulated

signals to be generated on the PWMx output pins. The four PWM signals can have the

same frequency (fPWM) or two different frequencies depending on the ENCNTR2 bit which

enables single timer or dual timer mode (see Figure 4 and Figure 5).

Figure 4.

The dual 12-bit autoreload timer: single timer mode (ENCNTR2=0)

The PWM frequency is controlled by the counter period and the ATR register value following

formula

fPWM = fCOUNTER / (4096 - ATR)

(3.1)

ATIC

PWM0

PWM1

PWM2

PWM3

PWM3 Duty Cycle Generator

12-bit Input Capture

PWM2 Duty Cycle Generator

PWM1 Duty Cycle Generator

PWM0 Duty Cycle Generator

12-Bit Autoreload Register 1

12-Bit Upcounter 1

Clock

Control

Edge Detection Circuit

Output Compare

CMP

Interrupt

OVF1 Interrupt

OE0

OE1

OE2

OE3

Dead Time

Generator

DTE bit

BPEN bit

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