TDA5241 Datasheet, PDF (13/19 Pages) NXP Semiconductors – Brushless DC motor drive circuit

Philips Semiconductors
Brushless DC motor drive circuit
Product specification
TDA5241
fosc
=
where:
Kt = torque constant (N.m/A)
I = current (A)
p = number of magnetic pole-pairs
J = inertia J (kg/m2)
Example: J = 72 x 10-6 kg/m2, K = 25 x 10-3 N.m/A, p = 6 and I = 0.5 A; this gives f osc = 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 IlF, (choose 220 nF).
THE ADAPTIVECOMMUTATIONDELAY(CAP-CDM ANDCAP-CDS)
In this circuit capacitor CAP-CDM 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-CDM) is discharged at twice the charging
current. The charging current is 8.1 IlA and the discharging current 16.2 IlA ; 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=
8.1
:rx1:3
-5
-~
-fC1
(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 Vat 16.2 J.lA.
maximum delay = (0.076 x C) ms (witch C in nF)
Example: nominal commutation frequency = 900 Hz and the lowest usable frequency = 400 Hz, so:
CAP-CDM = ^6420301= 15.6 (choose 18 nF)
The other capacitor, CAP-CDS, is used to repeat the same delay by charging and discharging with 20 ~A.
The same value can be chosen as for CAP-CDM. Figure 7 illustrates typical voltage waveforms
voltage
on CAP-CD
-Vmax=Vih
-Vil
8
March 1997
Fig.7 CAP-CD and CAP-DC typical voltage waveforms in normal running mode.
(ZCR = Zero-crossing ; COM = COMMUTATION)
13/19