DB62 Datasheet, PDF (1/6 Pages) Cirrus Logic – DEMONSTRATION BOARD FOR SA305EX

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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
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.
HALLA
0
0
0
1
1
1
0
0
0
1
1
1
Sensor Output
Driver Output
HALLB
HALLC ØC (OUTC) ØB (OUTB)
CCW Rotation Facing Lead End
0
1
X
HI
1
1
HI
X
1
0
HI
LO
1
0
X
LO
0
0
LO
X
0
1
LO
HI
CW Rotation Lead End
1
0
LO
HI
1
1
LO
X
0
1
X
LO
0
1
HI
LO
0
0
HI
X
1
0
X
HI
ØA (OUTA)
LO
LO
X
HI
HI
X
X
HI
HI
X
LO
LO
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.
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