TDA5240T Datasheet, PDF (12/19 Pages) NXP Semiconductors – Brushless DC motor drive circuit

Philips
Semiconductors
Brushless DC motor drive circuit
Product specification
TDA5240T
Analog control of the motor output voltages is achieved by an internal operational amplifier which tranfer gain is internally
fixed. Compensation of the motor pole is done by an external capacitor (CAP CPC).
Both grounds GND1 and GND2 must be connected together.
ADJUSTMENTS
The system has been designed in such a way that the tolerances of the application components are not critical. However,
the approximate values of the following components must still be determined:
.The start capacitor; this determines the frequency of the start oscillator
.The two capacitors in the adaptive commutation delay circuit. These are important in determining the optimum moment
for commutation, depending on the type and loading of the motor
~ The timing capacitor; this provides the system with its timing signals
(This deals with the application note AN94070)
THE START CAPACITORS (CAP-ST)
This capacitor determines the frequency of the start oscillator. It is charged and discharged, with a current of 2 ~A, from
0.05 to 2.2 V and back to 0.05 V. The time taken to complete one cycle is given by:
tstart = (2.15 X C)s
(with C in ~F)
The start oscillator is reset by a commutation pulse and so is only active when the system is in the start-up mode. A pulse
from the start oscillator will cause the outputs to change to the next state (torque in the motor) .If the movement of the motor
generates enough EMF the TDA5240T will run the motor. If the amount of EMF generated is insufficient, then the motor will
move one step only and will oscillate in its new position.
The amplitude of the oscillation must decrease sufficiently before the arrival of the next start pulse, to prevent the pulse
arriving during the wrong phase of the oscillation. The oscillation of the motor is given by:
1
= ¥ x ( Kt x I x J )2
'osc
November 96
12/19