TDA5149 datasheet(8/28 Pages) PHILIPS

8 / 28 page

1996 May 06

Philips Semiconductors

Product speciﬁcation

12 V Voice Coil Motor (VCM) driver and

spindle motor pre-driver combination chip

TDA5149G

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.

The different control modes of the TDA5149G can be

commanded via the serial bus. These modes are as

follows:

• 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.

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

VGAINSEL bit. This bit can be programmed via the serial

bus. A sense resistor (Rs) allows the measurement of the

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 (VCMSENSOUT) is fed back

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.

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