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TDA5144

Brushless DC motor drive circuit

Philips Electronics 

Philips Semiconductors

Brushless DC motor drive circuit

The oscillation of the motor is given by:

fosc

=

----------------1------------------

2π -K----t---×---J-I---×-----p--

where:

Kt = torque constant (N.m/A)

I = current (A)

p = number of magnetic pole-pairs

J = inertia J (kg.m2)

Example: J = 72 × 10−6 kg.m2, K = 25 × 10−3 N.m/A, p = 6

and I = 0.5 A; this gives fosc = 5 Hz. If the damping is high

then a start frequency of 2 Hz can be chosen or

t = 500 ms, thus C = 0.5/2 = 0.25 µF (choose 220 nF).

THE ADAPTIVE COMMUTATION DELAY (CAP-CD AND

CAP-DC)

In this circuit capacitor CAP-CD is charged during one

commutation period, with an interruption of the charging

current during the diode pulse. During the next

commutation period this capacitor (CAP-CD) is discharged

at twice the charging current. The charging current is

8.1 µA and the discharging current 16.2 µA; the voltage

range is from 0.9 to 2.2 V. The voltage must stay within

this range at the lowest commutation frequency of

interest, fC1:

C = -8---.--1f---×-×----1-1--.--03---–---6 = 6---f-2-C--3--1--1- (C in nF)

If the frequency is lower, then a constant commutation

delay after the zero-crossing is generated by the discharge

from 2.2 to 0.9 V at 16.2 µA;

maximum delay = (0.076 × C) ms (with C in nF).

Example: nominal commutation frequency = 900 Hz and

the lowest usable frequency = 400 Hz; so:

CAP-CD = 6--4--2--0-3--0--1- = 15.6 (choose 18 nF)

The other capacitor, CAP-DC, is used to repeat the same

delay by charging and discharging with 15.5 µA. The same

value can be chosen as for CAP-CD. Figure 9 illustrates

typical voltage waveforms.

June 1994

11

Product specification

TDA5144

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