TDA5142 Philips Semiconductors, TDA5142 Datasheet - Page 12

• Manufacturer Part Number: TDA5142
• Description: Brushless DC motor drive circuit
• Manufacturer: Philips Semiconductors

Philips Semiconductors
If the movement of the motor generates enough EMF the
TDA5142T 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:
where:
Example: J = 72
and I = 0.5 A; this gives f
then a start frequency of 2 Hz can be chosen or
t = 500 ms, thus C = 0.5/2 = 0.25 F (choose 220 nF).
T
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 A and the discharging current 16.2 A; 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, f
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 20 A;
maximum delay = (0.076
Example: nominal commutation frequency = 900 Hz and
the lowest usable frequency = 400 Hz; so:
The other capacitor, CAP-DC, is used to repeat the same
delay by charging and discharging with 15.5 A. The same
value can be chosen as for CAP-CD. Figure 7 illustrates
typical voltage waveforms.
June 1994
CAP-CD
f
C
osc
HE ADAPTIVE COMMUTATION DELAY
K
I = current (A)
p = number of magnetic pole-pairs
J = inertia J (kg.m
Brushless DC motor drive circuit
=
t
= torque constant (N.m/A)
=
8.1 10
------------------------- -
f 1.3
---------------------------------- -
2
C1
=
:
K
---------------------- -
6231
------------ -
400
1
t
–
6
J
I p
=
10
=
6231
------------ -
2
f
C1
).
15.6
6
kg.m
osc
(C in nF)
(choose 18 nF)
C) ms (with C in nF)
= 5 Hz. If the damping is high
2
, K = 25
(CAP-CD
10
3
N.m/A, p = 6
AND
12
Product specification
TDA5142T