TDA5146T Philips Semiconductors, TDA5146T Datasheet - Page 13

• Manufacturer Part Number: TDA5146T
• Description: Brushless DC motor drive circuit
• Manufacturer: Philips Semiconductors

motor winding; however, it must be short enough to detect reverse rotation. If the watchdog time is made too long, then the motor may run in the
Philips Semiconductors
The Timing Capacitor (CAP–TI)
Capacitor CAP–TI is used for timing the successive steps within one commutation period; these steps include some internal delays.
The most important function is the watchdog time in which the motor EMF has to recover from a negative diode–pulse back to a positive EMF
voltage (or vice versa). A watchdog timer is a guarding function that only becomes active when the expected event does not occur within a
predetermined time.
The EMF usually recovers within a short time if the motor is mining normally ( << ms ). However, if the motor is motionless or rotating in the
reverse direction, then the time can be longer ( >> ms ).
A watchdog time must be chosen so that it is long enough for a motor without EMF (still) and eddy currents that may stretch the voltage in a
wrong direction (with little torque).
The capacitor is charged, with a current of 57 A, from 0.2 to 0.3V. Above this level it is charged, with a current of 5 A, up to 2.2 V only if the
selected motor EMF remains in the wrong polarity (watchdog function). At the end, or, if the motor voltage becomes positive, the capacitor is
discharged with a current of 28 A. The watchdog time is the time taken to charge the capacitor, with a current of 5 A, from 0.3 to 2.2V. The
value of CAP–T1 is given by:
Example: If after switching off, the voltage from a motor winding is reduced, in 3.5 ms, to within 20 mv (the offset of the EMF comparator), then
the value of the required timing capacitor is given by:
Typical voltage waveforms are illustrated by Figure 9.
1994 May 18
Brushless DC motor drive circuit
C=5
C = 2.63
10
–6
3.5 = 9.2
VOLTAGE
ON CAP–TI
VMOT1
t
m
/1.9–2.63 t
voltage
on CAP-CDM
voltage
on CAP-CDS
Figure 9. Typical Cap–TI and VMOT1 voltage waveforms in normal running mode
Figure 8. CAP-CDM and CAP-CDS voltage waveform in normal running mode
m
(C in nF; t in ms)
(choose 10 nF)
13
TDA5146T
SL01522
SL01523
Product specification