TDA5145 Datasheet, PDF (10/24 Pages) NXP Semiconductors – Brushless DC motor drive circuit

Philips Semiconductors
Brushless DC motor drive circuit
APPLICATION INFORMATION
Product specification
TDA5145
(1) Value selected for 3 Hz start-up oscillator frequency.
Fig.7 Application diagram without use of the operational transconductance amplifier (OTA).
Introduction (see Fig.8)
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 (H) and one sinking
(L). The third output presents a high impedance (Z) to the
motor, which enables measurement of the motor
back-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. In Table 1 the
sequence of the six possible states of the outputs has
been depicted.
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.
Table 1 Output states.
STATE
MOT1⁽¹⁾
1
Z
2
H
3
H
4
Z
5
L
6
L
MOT2⁽¹⁾
L
L
Z
H
H
Z
Note
1. H = HIGH state;
L = LOW state;
Z = high-impedance OFF-state.
MOT3⁽¹⁾
H
Z
L
L
Z
H
The detected zero-crossings are used to provide speed
information. The information has been made available on
the FG output pin. This is an open collector output and
provides an output signal with a frequency that is half the
commutation frequency.
The system will only function when the EMF voltage from
the motor is present. Therefore, a start oscillator is
June 1994
10