TDA5140A Datasheet, PDF (16/24 Pages) NXP Semiconductors – Brushless DC motor drive circuit

Philips Semiconductors
Brushless DC motor drive circuit
Product specification
TDA5140A
THE OPERATIONAL TRANSCONDUCTANCE AMPLIFIER (OTA)
The OTA is an uncommitted amplifier with a high output
current (40 mA) that can be used as a control amplifier.
The common mode input range includes ground (GND)
and rises to V_P − 1.7 V. The high sink current enables the
OTA to drive a power transistor directly in an analog
control amplifier.
Although the gain is not extremely high (0.3 S), care must
be taken with the stability of the circuit if the OTA is used
as a linear amplifier as no frequency compensation has
been provided.
The convention for the inputs (inverting or not) is the same
as for a normal operational amplifier: with a resistor (as
load) connected from the output (AMP OUT) to the positive
supply, a positive-going voltage is found when the
non-inverting input (+AMP IN) is positive with respect to
the inverting input (−AMP IN). Confusion is possible
because a 'plus' input causes less current, and so a
positive voltage.
RELIABILITY
It is necessary to protect high current circuits and the
output stages are protected in two ways:
• Current limiting of the 'lower' output transistors. The
'upper' output transistors use the same base current as
the conducting 'lower' transistor (+15%). This means
that the current to and from the output stages is limited.
• Thermal protection of the six output transistors is
achieved by each transistor having a thermal sensor
that is active when the transistor is switched on. The
transistors are switched off when the local temperature
becomes too high.
It is possible, that when braking, the motor voltage (via the
flyback diodes and the impedance on VMOT) may cause
higher currents than allowed (>0.6 A). These currents
must be limited externally.
MOTOR CONTROL
DC motors can be controlled in an analog manner using
the OTA.
For the control an external transistor is required. The OTA
can supply the base current for this transistor and act as a
control amplifier (see Fig.7).
April 1994
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