TDA5341 Datasheet, PDF (10/28 Pages) NXP Semiconductors – Brushless DC motor and VCM drive circuit with speed control

Philips Semiconductors
Brushless DC motor and VCM drive circuit
with speed control
Product specification
TDA5341
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:
f_osc
=
0--_Π--.--5-
×


K_t
×
I
×
P-J--


12--
Where:
K_t = torque constant (N.m/A)
I = current (A)
p = number of magnetic pole-pairs
J = inertia J (kg/m²).
Example: J = 6.34 × 10^−7 kg/m², K = 4.5 × 10^−3 N.m/A,
p = 6 and I = 0.48 A; thus f_osc = 22.7 Hz. Without
damping, a start frequency of 48.4 Hz can be chosen or
t = 24 ms, thus C = 0.024/0.78 = 0.031 µF, (choose
33 nF).
The Adaptive Commutation Delay
(CAPCDM and CAPCDS)
In this circuit capacitor CAPCDM is charged during one
commutation period, with an interruption of the charging
current during the diode pulse.
During the next commutation period this capacitor
(CAPCDM) is discharged at twice the charging current.
The charging current is 10 µA and the discharging current
20 µA; the voltage range is from 0.87 to 2.28 V.
The voltage must stay within this range at the lowest
commutation frequency of interest, f_C1:
C = ^1---f-0--_×---^×--1---1.--4-0--1-^–---⁶- = ^7---f-0-_C--9--₁--2-
Where C is in nF.
If the frequency is lower, then a constant commutation
delay after the zero-crossing is generated by the discharge
from 2.28 to 0.87 V at 20 µA.
Maximum delay = (0.070 × C) ms: Where C is in nF.
Example: nominal commutation frequency is 3240 Hz and
the lowest usable frequency is 1600 Hz, thus
CAPCDM = 7092/1600 = 4.43 (choose 4.7 nF)
The other capacitor, CAPCDS, is used to repeat the same
delay by charging and discharging with 20 µA. The same
value can be chosen as for CAPCDM. Figure 3 illustrates
typical voltage waveforms.
handbook, full pagewidth
voltage
on CAPCDM
voltage
on CAPCDS
MGE820
1997 Jul 10
Fig.3 CAPCDM and CAPCDS voltage waveforms in normal running mode.
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