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1

M I C R O T E C H N O L O G Y

DB62

Table 1. Commutation Table.

The algorithm for the microcontroller is shown in figure 1. The program for Microchip® PIC 18F2331 is available for download

on www.apexmicrotech.com.

INTRODUCTION

The DB62 is designed to demonstrate the capabilities of

the SA305 as a 3 phase brushless DC motor driver IC. The

PWM inputs to the SA305 are controlled by an on-board

microcontroller. The EVAL49 board is pre-wired for all required

and recommended external components. Please refer to ap-

plications note 32 in the Apex catalog for guidance in filter

component selection. The 1µF ceramic capacitors supplied with

the kit are for high frequency bypassing of the VS and VDD

supplies (C1, C11, C4 and C7 on the EVAL49 schematic). Two

additional 100uF bypass capacitors are provided with the kit

for the VS supplies (C2 and C12 on the EVAL49 schematic).

Please refer to applications note 30 for help with power supply

bypassing and other useful information.

PWM CONTROL IN DB62

BLDC motors are electronically commutated based on the

rotor position. The stator windings are energized in a sequence

based upon the combination of three Hall sensor signals which

provide the rotor position. In the DB62 the SA305 input PWM

control is achieved by means of by an on-board Microchip®

PIC 18F2331 microcontroller. The sequence table for com-

mutation (obtained from the motor data sheet) is entered in

Sensor Output

Driver Output

HALLA

HALLB

HALLC

ØC (OUTC)

ØB (OUTB)

ØA (OUTA)

CCW Rotation Facing Lead End

0

0

1

X

HI

LO

0

1

1

HI

X

LO

0

1

0

HI

LO

X

1

1

0

X

LO

HI

1

0

0

LO

X

HI

1

0

1

LO

HI

X

CW Rotation Lead End

0

1

0

LO

HI

X

0

1

1

LO

X

HI

0

0

1

X

LO

HI

1

0

1

HI

LO

X

1

0

0

HI

X

LO

1

1

0

X

HI

LO

the program memory of the microcontroller. Hall sensors A, B

and C are connected to the IC pins of the Input Capture (IC)

module in the PIC18F2331. This module interrupts on every

transition on any of the IC pins. Upon interrupt, the interrupt

service routine reads all the three inputs and loads the correct

sequence for commutation. The following PWM control features

are programmed in the MCU provided with the DB62:

1. User Controlled PWM frequency using external potentiom-

eter (VFREQ in EVAL 49 board). The PWM frequency can

be varied from 4 KHz to 118 KHz.

2. User Controlled PWM duty cycle using external potenti-

ometer (VDUC in EVAL49 board). The voltage set by the

potentiometer will act as a ‘Speed Reference’. The duty

cycle can be varied from 0 % to 98 %.

The Forward/Reverse button is provided to control the

direction of the motor. Depending upon the direction, the cor-

responding hall sensor commutation sequence is used and the

PWM signals are generated accordingly. The START/STOP

button can be used to run or stop the motor.

As mentioned earlier, the MCU provided with the kit is pre-

programmed for all of the features described above. The hall

sensor commutation table that has been used in programming

the MCU is shown in table 1.