TDA5149G Philips Semiconductors, TDA5149G Datasheet - Page 8

• Manufacturer Part Number: TDA5149G
• Description: 12 V Voice Coil Motor VCM driver and spindle motor pre-driver combination chip
• Manufacturer: Philips Semiconductors

Philips Semiconductors
FUNCTIONAL DESCRIPTION
Spindle
The spindle section contains both the low and high side
pre-drivers for a three phase DC brushless motor.
The digital commutation control, using the timing
information provided via the serial port, is responsible for
the proper switch-on and switch-off of the external power
FETs. It is also responsible for selecting the correct BEMF
comparator.
For optimum power efficiency, a continuous PWM method
is used to control the average current from the power
supply to the motor coils. This PWM mode, by controlling
the average power supply current, produces a lower
torque ripple and thus lower audible noise. In order to
reduce further acoustic noise the TDA5149G is provided
with a soft switching circuit to turn-on and turn-off linearly
the switching current under PWM control. The switching
transition time is controlled by the digital commutation
circuit and is fixed to 50% of the time between two
zero-crossings, i.e. 30 of the electrical revolution.
Soft switching is achieved by activating, during
commutation, a free-running duty-cycle modulator
controlled by a linearly decreasing voltage across a
capacitor. This will reduce the current smoothly in the
off-going leg to zero. In conjunction with this additional
PWM open loop, the average current control regulates the
sum of the current in the off-going and on-going leg.
This method requires two PWM control loops; one to
control the average current (main loop) and one to control
the current in the off-going leg. The swapping of the two
loops is realized with a pair of analog switches that are
sequentially switched by the digital commutation circuitry.
The PWM control also causes PWM pulses on the back
EMF. These pulses disturb correct sensing of the back
EMF for the zero-crossing detection. Consequently,
edge-triggered latches are inserted behind the back EMF
comparators, thus ensuring reliable back EMF sensing.
In the SPINMODE, programmable via the serial bus, the
user can feed their own commutation pulses to the
pre-drivers and control the motor in the stepper-motor
mode. The commutation pulses are applied to the
TDA5149G via the serial bus by setting the COMMCLK bit
successively to logic 1 and logic 0.
1996 May 06
12 V Voice Coil Motor (VCM) driver and
spindle motor pre-driver combination chip
8
The different control modes of the TDA5149G can be
commanded via the serial bus. These modes are as
follows:
Voice coil motor
The VCM is a linear, symmetrical, class AB, H-bridge type
power amplifier with all power devices on-chip. The driver
is a transconductance amplifier that controls the output
currents up to 1.65 A. The driver is constructed in a
master-slave configuration with the zero current level
internally adjusted in such a way that it corresponds to the
middle of the output swing. Moreover, the gain of the slave
has been made greater than 1 in order to ensure full
saturation of the driver output VCM+.
The gain of the closed loop is programmable, using the
V
bus. A sense resistor (R
VCM current. The voltage across this resistor is connected
to an accurate sense amplifier with a typical gain of 5.
The output of the sense amplifier (V
to the input of the VCM amplifier. Because of the symmetry
of the circuit, the compensation network can be connected
between the VCM1 input and the VCM output.
Control modes such as VCM-BRAKE, VCM-DISABLE and
VCM-PARK can be controlled via the serial bus.
Latch drivers
The TDA5149G provides the possibility of driving an
external latch to secure the VCM heads. There are two
modes; the activate mode (LACTIVE) and the hold mode
(LHOLD). The hold mode is used to preserve power.
Both modes are controlled via the serial bus. The drivers
are switched off during the SLEEP mode or in the event of
a power-down.
GAINSEL
Sleep mode: all analog circuits, except the power supply
monitor, are switched off to reduce the power
consumption of both the 12 and 5 V supplies.
Disable mode: the output voltage of all pre-drivers is
LOW thus the external power MOSFETs are not
conducting.
Brake mode: all low side pre-drivers are turned on
(output voltage HIGH) thus switching on the low-side
power MOSFETs. In this way the back EMF voltage of
the motor is short-circuited to ground.
bit. This bit can be programmed via the serial
s
) allows the measurement of the
CMSENSOUT
Product specification
TDA5149G
) is fed back