TDA5241 Datasheet, PDF (10/19 Pages) NXP Semiconductors – Brushless DC motor drive circuit

Philips Semiconductors
8 _{Brushless DC motor drive circuit}
Product
specification
TDA5241
APPLICATION INFORMATION
Introduction
Figure 5 shows full-wave driving of a three phase motor requires three push-pull output stages. In each of the six possible
states two outputs are active, one sourcing and one sinking current. The third output presents a high impedance to the
motor which enables measurement of the motor EMF in the corresponding motor coil by the EMF comparator at each
output. The commutation logic is responsible for control of the output transistors and selection of the correct EMF
comparator.
The zero-crossing in the motor EMF (detected by the comparator selected by the commutation logic) is used to calculate
the correct moment for the next commutation, that is, the change to the next output state. The delay is calculated
(depending on the motor loading) by the adaptive commutation delay block.
Because of high inductive loading the output stages contain flyback diodes. The output stages are also protected by a
current limiting circuit and by thermal protection of the six output transistors.
8 The zero-crossings can be used to provide speed information such as the tacho signal FG. A VCR scanner also requires
a PG phase sensor. This circuit has an interface for a simple pick-up coil. A multiplexer circuit is also provided to combine
the FG and PG signals in time. The TDA 5240 is providing 1 multiplexed FG PG signal: pin7 (8020) FG-PG 3 times the
number of pole pairs. A PG output signal is generated; pulse width is typically 7 ~s.
Table 1 OUTPUT STATES
STATE
1
2
3
4
5
6
MOT1
Z
H
H
Z
L
L
MOT2
L
L
Z
H
H
Z
MOT3
H
Z
L
L
-Z
H
8 In Table1 , the sequence of the six possible states of the outputs has been depicted
8
March 1997
10/19