Philips SZA1010T Datasheet

INTEGRATED CIRCUITS

DATA SH EET

SZA1010

Digital Servo Driver 3 (DSD-3)

Preliminary speciﬁcation File under Integrated Circuits, IC01

1997 Apr 07

Philips Semiconductors Preliminary speciﬁcation

Digital Servo Driver 3 (DSD-3) SZA1010

FEATURES Servo functions

• 1-bit class-D focus actuator driver (4 Ω)

• 1-bit class-D radial actuator driver (4 Ω)

• 1-bit class-D sledge motor driver (2 Ω).

Other features

• Supply voltage 5 V only

• Small package (SOT163-1)

• Higher efficiency, compared with conventional drivers,

due to the class-D principle

• Built-in digital notch filters for higher efficiency

• Enable input for focus and radial driver

• Enable input for sledge driver

• 3-state input for radial driver

• Doubled clock frequency

• Differential outputs for all drivers

• Separate power supply pins for all drivers.

QUICK REFERENCE DATA

GENERAL DESCRIPTION

The SZA1010 or Digital Servo Driver 3 (DSD-3) consists of 1-bit class-D power drivers, which are specially designed for digital servo applications. Three such amplifiers are integrated in one chip, to drive the focus and radial actuators and the sledge motor of a compact disc optical system.

The main benefits of using this principle are its higher efficiency grade compared to conventional analog power amplifiers, its higher integration level, its differential output and the fact that only a few external components are needed. When using these digital power drivers in a digital servo application, the statement ‘complete digital servo loop’ becomes more realistic.

SYMBOL PARAMETER MIN. TYP. MAX. UNIT

DDD

DDA(F)

DDA(R)

DDA(S)

DDDq

DDA(F)

DDA(R)

DDA(S)

i(clk)

tot

amb

digital supply voltage 4.5 − 5.5 V analog supply voltage focus actuator 4.5 − 5.5 V analog supply voltage radial actuator 4.5 − 5.5 V analog supply voltage sledge actuator 4.5 − 5.5 V quiescent digital supply current −−10 µA analog supply current focus actuator − 126 250 mA analog supply current radial actuator − 20 250 mA analog supply current sledge actuator − 150 560 mA input clock frequency − 8.4672 10 MHz total power dissipation − tbf − mW operating ambient temperature −40 − +85 °C

ORDERING INFORMATION

TYPE

NUMBER

NAME DESCRIPTION VERSION

PACKAGE

SZA1010T SO20 plastic small outline package; 20 leads; body width 7.5 mm SOT163-1

1997 Apr 07 2

Philips Semiconductors Preliminary speciﬁcation

Digital Servo Driver 3 (DSD-3) SZA1010

BLOCK DIAGRAM

book, full pagewidth

RAC

FOC

SLC

CLI

EN1 EN2

7 8

SZA1010

CONTROL

DDA(R)

DDD

613141

DIGITAL

NOTCH FILTER

DIGITAL

NOTCH FILTER

DIGITAL

NOTCH FILTER

5101718

SSA(R)

SSD

3-STATE

DDA(F)

DDA(S)

END STAGE

H−BRIDGE

END STAGE

H−BRIDGE

END STAGE

H−BRIDGE

SSA(S)/VSSA(F)

RA+

RA−

FO+

FO−

SL+

SL−

MBK013

Fig.1 Block diagram.

1997 Apr 07 3

Philips Semiconductors Preliminary speciﬁcation

Digital Servo Driver 3 (DSD-3) SZA1010

PINNING

SYMBOL PIN DESCRIPTION

DDA(S)

SLC 2 PDM input for sledge driver FOC 3 PDM input for focus driver RAC 4 PDM input for radial driver V

SSD

DDD

CLI 7 clock input EN1 8 enable input 1 EN2 9 enable input 2 V

SSA(R)

RA+ 11 radial driver (positive output) RA− 12 radial driver (negative output) V

DDA(R)

DDA(F)

FO+ 15 focus driver (positive output) FO− 16 focus driver (negative output) 3-STATE 17 radial 3-state input

SSA(S)

SSA(F)

SL+ 19 sledge driver (positive output) SL− 20 sledge driver (negative output)

analog supply voltage for sledge

motor driver

5 digital ground 6 digital supply voltage

10 analog ground for radial driver

analog supply voltage for radial

driver

14 analog supply voltage for focus

analog ground for sledge

driver/focus

handbook, halfpage

DDA(S)

SSA(R)

1 2

SLC

FOC

RAC

SSD

DDD

CLI EN1 EN2 RA−

6 7 8 9

SZA1010

MBK012

Fig.2 Pin configuration.

SL− SL+

SSA(S)/VSSA(F)

3-STATE

17 16

FO−

FO+ V

DDA(F)

DDA(R)

12 11

RA+

1997 Apr 07 4

Philips Semiconductors Preliminary speciﬁcation

Digital Servo Driver 3 (DSD-3) SZA1010

FUNCTIONAL DESCRIPTION Principle of a class-D digital power driver

Figure 3 shows the block diagram of one of the digital drivers integrated in the DSD-3. It consists of a timing block and four CMOS switches. The input signal is a 1-bit Pulse Density Modulated (PDM) signal, the output of the digital servo ICs.

The maximum operating clock frequency of the device is 10 MHz. In combination with most frequently used Philips digital servo ICs, the operating frequency of the digital drivers is 8.4672 MHz (192 × 44.1 kHz). The sampling frequency of the 1-bit code however is 2.1168 MHz, so internally in the DSD-3 the clock speed of the switches will be 2.1168 MHz. The higher input clock frequency is used to make non-overlapping pulses to prevent short-circuits between the supply voltages. For the control of the switches, two states can be distinguished. If the 1-bit code contains a logic 1, switches A and D are closed and current will flow in the direction as shown in Fig.4.

If the 1-bit code contains a logic 0, switches B and C are closed and current will flow in the opposite direction, as shown in Fig.5.

This indicates that the difference between the mean number of ones and zeros in the PDM signal determines the direction in which the actuator or motor will rotate.

If the mean number of ones and zeros is equal (Idle mode) the current through the motor or actuator is alternated between the positive and negative direction at a speed of half the sample frequency of 2.1168 MHz. This results in a high dissipation and the motor does not move.

The amplitude transfer as a function of frequency is given in Fig.7.

Figure 7 shows that the filter has a zero on filtering out the Idle pattern (101010). The output of this filter is a three-level code (1.5-bit). For the control of the switches three states (1.5-bit) can be distinguished: the two states as described earlier and a third one. This state is used when an idling pattern is supplied.

Switches C and D are closed (see Fig.8). In this Idle mode, no current will flow and thus the efficiency will be improved. This mode is also used to short-circuit the inductive actuator/motor. In this way, high induction voltages are prevented because the current can commutate via the filter and the short-circuit in the switches. All three drivers (radial, focus and sledge) contain a digital notch filter as described (see Fig.6). Each driver has its own power supply pins to reduce crosstalk due to of the relative high current flowing through the pins.

Compared to the DSD-2, the DSD-3 has a 3-state mode for the radial output, which is useful when active damping of the radial actuator is needed. When fast access times are required, the sledge has to move with high accelerations. To prevent the radial actuator from moving too far from its centre position due to the acceleration, active damping is applied. In order to measure the displacement of the radial actuator, the voltage induced by the actuator itself is measured, which is proportional to its speed. The damping consists of a sequence of controlling, waiting, measuring and controlling etc. To be able to measure the induced voltage properly, the influence of the DSD-3 is eliminated by switching it into 3-state mode.

⁄2fs, thereby

To improve the efficiency, a digital notch filter is added at the input of the digital drivers. This filters the Idle mode pattern (1010101010 etc.) see Fig.6.

1997 Apr 07 5

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