TDA5140A Datasheet, PDF (10/24 Pages) NXP Semiconductors – Brushless DC motor drive circuit

Philips Semiconductors
Brushless DC motor drive circuit
Product specification
TDA5140A
Introduction (see Fig.7)
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.
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
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.
The detected zero-crossings are used to provide speed
information. The information has been made available on
the PG/FG output pin. This is an open collector output and
provides an output signal with a frequency that is half the
commutation frequency. 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 system will only function when the EMF voltage from
the motor is present. Therefore, a start oscillator is
provided that will generate commutation pulses when no
zero-crossings in the motor voltage are available.
A timing function is incorporated into the device for internal
timing and for timing of the reverse rotation detection.
The TDA5140A also contains an uncommitted
transconductance amplifier (OTA) that can be used as a
control amplifier. The output is capable of directly driving
an external power transistor.
The TDA5140A is designed for systems with low current
consumption: use of I²L logic, adaptive base drive for the
output transistors (patented), possibility of using a pick-up
coil without bias current.
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.
April 1994
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