TDA5341 Datasheet, PDF (9/28 Pages) NXP Semiconductors – Brushless DC motor and VCM drive circuit with speed control

Philips Semiconductors
Brushless DC motor and VCM drive circuit
with speed control
Product specification
TDA5341
Uncontrolled modes
POWER SHUT-DOWN
If the power supply decreases to less than the voltage
threshold determined by the ratio between R1 and R2
connected to UVDIN2 (see Fig.8) (for more than 1 µs), the
TDA5341 will issue a reset (RESETOUT goes LOW) and
the following operation will start:
• Firstly, the MOT outputs are switched to the high
impedance state so as to get back the rectified EMF
issued from the motor itself. At the same time, the
voltage upper converter is cut off in order to preserve the
voltage on the charge pump capacitance at CAPCP.
The energy supplied in that way is then used to park the
heads in a safe position
• Secondly, after a certain period of time, depending on
the RC constant of the device connected to
BRAKEDELAY, the lower MOS drivers will be turned on
in order to stop the motor completely.
THERMAL SHUT-DOWN
Should the temperature of the chip exceed +140 ±10 °C, a
shut-down operation will also be processed. The actions
described for power shut-down will be sequenced in the
same manner.
SPINDLE SECTION (see Fig.1)
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 current 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, i.e.
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.
The zero-crossings can be used to provide speed
information such as the tacho signal (FG).
The system will only function when the EMF voltage from
the motor is present. Consequently, 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 TDA5341 also contains a control amplifier, directly
driving output amplifiers.
The TDA5341 also provides access to the user of some of
its internal test modes. Firstly, a PRESET mode can be
used for prepositioning the three motor output drivers into
a fixed state. By pulling pin PRESET to 0.75 V above V_DD,
MOT3 goes HIGH, MOT2 goes LOW and MOT1 goes to
the high impedance state.
In addition, when TESTIN is pulled HIGH (provided that
FREDENA is LOW), the 3 motor output drivers are
switched off. It should be noted that RESETOUT goes
LOW in that particular event.
Adjustments
The system has been designed in such a way that the
tolerances of the application components are not critical.
However, the approximate values of the following
components must still be determined:
• The start capacitor; this determines the frequency of the
start oscillator
• The two capacitors in the adaptive commutation delay
circuit; these are important in determining the optimum
moment for commutation, depending on the type and
loading of the motor
• The timing capacitor; this provides the system with its
timing signals.
The start capacitor (CAPST)
This capacitor determines the frequency of the start
oscillator. It is charged and discharged, with a current of
5.5 µA, from 0.05 to 2.2 V and back to 0.05 V. The time
taken to complete one cycle is given by:
t_start = (0.78 × C); where C is given in µF.
The start oscillator is reset by a commutation pulse and so
is only active when the system is in the start-up mode.
A pulse from the start oscillator will cause the outputs to
change to the next state (torque in the motor). If the
movement of the motor generates enough EMF the
TDA5341 will run the motor.
1997 Jul 10
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