Philips TZA1025T-V2 Datasheet

DATA SH EET

Product speciﬁcation File under Integrated Circuits, IC01

1998 Oct 30

INTEGRATED CIRCUITS

TZA1025

Data amplifier and laser supply circuit for CD audio and video optical systems (ADALASLC)

1998 Oct 30 2

Philips Semiconductors Product speciﬁcation

Data ampliﬁer and laser supply circuit for CD audio and video optical systems (ADALASLC)

TZA1025

FEATURES

• Supports a wide range of voltage output mechanisms

• RF amplifier designed for audio and video applications with 1 × data rate

• Programmable RF gain for CD-Audio/Video (CD-A/V)

and CD-Read/Write (CD-R/W) discs

• Equalizer for optimal performance

• Fully Automatic Laser Power Control (ALPC) including

stabilization plus a separate laser supply voltage for power efficiency

• Adjustable current range of ALPC output

• Automatic N- or P-substrate monitor diode selection

• Adjustable laser bandwidth and laser switch-on current

slope using external capacitor

• Protection circuit to prevent laser damage due to laser supply voltage dip

• Optimized interconnection between data amplifier and Philips’ digital signal processor CD10LC (SAA7325)

• Wide supply voltage range

• Power-down switch to reduce power consumption

during standby

• Low power consumption.

GENERAL DESCRIPTION

The TZA1025 is a data amplifier and laser supply circuit for voltage output mechanisms found in a wide range of audio and video CD systems. The device contains an RF amplifier and an automatic laser power control circuit.

The preamplifier forms an interface for voltage output CD mechanisms to the Philips’ digital signal processor CD10LC (SAA7325).

The RF bandwidth allows this device to be used in CD-A/V applications with a data rate of n = 1 times speed. The RF gain can be adapted for CD-A/V discs or CD-R/W discs by means of the gain select signal.

The equalizer ensures an optimal performance. The TZA1025 can be adapted to a wide range of voltage

output mechanisms by means of external resistors. The ALPC circuit will maintain control over the laser diode

current. With an on-chip reference voltage generator, a constant and stabilized output power is ensured independent of ageing. The ALPC can accommodate N- or P-substrate monitor diodes.

A separate supply voltage connection for the laser allows the internal power dissipation to be reduced by connecting a low voltage supply. The laser output current range can be optimized to fit the requirements of the laser diode by means of one external resistor. When a DC-to-DC converter is used, in combination with the control loop of the ALPC, the adjustable output current range provides the possibility to compensate for the extra gain a DC-to-DC converter introduces in the control loop.

ORDERING INFORMATION

TYPE

NUMBER

PACKAGE

NAME DESCRIPTION VERSION

TZA1025T SO14 plastic small outline package; 14 leads; body width 3.9 mm SOT108-1

1998 Oct 30 3

Philips Semiconductors Product speciﬁcation

Data ampliﬁer and laser supply circuit for CD audio and video optical systems (ADALASLC)

TZA1025

QUICK REFERENCE DATA

BLOCK DIAGRAM

SYMBOL PARAMETER CONDITIONS MIN. TYP. MAX. UNIT

Supplies

supply voltage 2.4 − 5.5 V

supply current − 3 − mA

DD(L)

laser supply voltage 2.4 − 5.5 V

RF ampliﬁer

d(f)(RF)

RF ﬂatness delay −− 10 ns

Laser supply circuit

o(LASER)(max)

maximum laser output current V

DD(L)

− V

o(LASER)

= 0.55 V 80 −−mA

i(mon)

monitor input voltage

N-substrate monitor diode − 0.150 − V P-substrate monitor diode − V

− 0.150 − V

Temperature range

amb

operating ambient temperature 0 − 70 °C

Fig.1 Block diagram.

(1) Band gap reference voltage.

handbook, full pagewidth

MBK902

250 kHz

TZA1025

3 7

V/I

DD(L)

GND

GAP

MON

(1)

DIN

CDRW

CFIL

PWRON

RGADJ

CMFB

RFFB

RFEQO

GND

1998 Oct 30 4

Philips Semiconductors Product speciﬁcation

Data ampliﬁer and laser supply circuit for CD audio and video optical systems (ADALASLC)

TZA1025

PINNING

FUNCTIONAL DESCRIPTION

The TZA1025 consists of two sections, the RF amplifier and the automatic laser power control circuit.

RF ampliﬁer

The RF amplifier consists of a current input amplifier, an equalizer/bandwidth section and a transimpedance output amplifier with an external feedback resistor of 10 kΩ(fixed value).

SYMBOL PIN DESCRIPTION

LD 1 current output to laser diode V

DD(L)

2 laser supply voltage CFIL 3 external ﬁlter capacitor MON 4 laser monitor diode input DIN 5 central diode input GND 6 ground PWRON 7 power-on select input CMFB 8 common mode feedback voltage

input RFFB 9 external RF feedback resistor RFEQO 10 RF ampliﬁer output CDRW 11 gain select input for CD-A/V, CD-R/W GND 12 ground V

13 supply voltage

RGADJ 14 external laser supply gain adjust

resistor

Fig.2 Pin configuration.

handbook, halfpage

MBK901

TZA1025

1 2 3 4 5 6 7

14 13 12 11 10

DD(L)

CFIL

MON

DIN

GND

PWRON

CMFB

RFFB

RFEQO

CDRW

GND

RGADJ

The gain of the RF amplifier can be adjusted by the external input resistors. Fig.3 shows the simplified schematic which can be used to determine the RF gain. The signal is AC coupled to the RF amplifier. The formula to determine the gain is shown below:

(1)

where:

GRF is the RF amplifier gain n is the number of input resistors Z

tr(RF)

is the transimpedance of the amplifier (Ω)

R2 is the value of the input resistors (Ω).

The gain can be increased by a factor of 4 by making pin CDRW HIGH. The value of Z

tr(RF)

is 9.8 kΩ for CD-A/V

(CDRW = LOW) and 38 kΩ for CD-R/W (CDRW = HIGH). An internal equalizer ensures an optimal performance. The DC output level of the amplifier can be set by applying

a DC voltage on the common mode feedback pin CMFB. Since the input signal is AC-coupled the RF output voltage will swing (symmetrically) around this DC level.

The coupling of the TZA1025 to the signal processor (SAA7325) can be either AC or DC. When an AC-coupling is chosen (see Fig.6) the minimum supply voltage can be applied. When a DC-coupling is chosen (see Fig.7) a minimum supply voltage of 2.8 V is required.

n–

tr RF()

------------------

×=

Fig.3 Simplified schematic.

handbook, halfpage

CDRW

RFEQO

10 kΩ

R2(1) R2(2)

R2(n)

MGL530

1998 Oct 30 5

Philips Semiconductors Product speciﬁcation

Data ampliﬁer and laser supply circuit for CD audio and video optical systems (ADALASLC)

TZA1025

Automatic laser power control circuit

The ALPC stabilises the laser output power thereby reducing the effect of ageing of the laser.

The TZA1025 automatically detects when an N- or P-substrate monitor diode is used and selects the correct reference voltage. A simplified diagram for the use of an N- or P-substrate monitor diode is given in Fig.4.

The gain of the loop can be controlled (reduced) by adding an external resistor between pins RGADJ and GND. The loop gain then becomes:

(2)

where:

loop

is the loop gain

ALPC

is the ALPC transfer (60 A/V) Glm is the laser-to-monitor transfer (V/A) G

con

is the extra gain introduced when a DC-to-DC

converter is used in the loop; G

con

= 1 when no

DC-to-DC converter is used 250 is a fixed internal resistor value (Ω) R

RGADJ

is the value of the external resistor (Ω).

The minimum available output current is also reduced when an external resistor is used. The formula to determine the minimum available output current is shown in equation (3).

(3)

loop

ALPCGlm

× G

con

250

250 R

RGADJ

-------------------------------------

×=

oIo(LASER)(max)

250

250 R

RGADJ

-------------------------------------

×=

where:

is output current (mA)

o(LASER)(max)

is the maximum laser output current (mA) 250 is a fixed internal resistor value (Ω) R

RGADJ

is the value of the external resistor (Ω).

The bandwidth of the loop is determined by the external filter capacitor C

CFIL

and the loop gain. The formula to

determine the bandwidth is shown in equation (4).

(4)

where:

CFIL

is the value of the capacitor (F)

loop

is the loop gain.

The TZA1025 has a protection circuit to prevent laser damage that can occur due to a dip of V

DD(L)

. When a dip occurs the output transistor (see Fig.4) will go into saturation making it unable to supply the required laser current. Without the protection circuit the ALPC would still try to supply the required laser current by charging the filter capacitor C

CFIL

. After the dip a fully charged capacitor would create a large output current during the few milliseconds it needs to discharge the capacitor to a normal level. The protection circuit monitors the output transistor and switches off the ALPC when saturation occurs by discharging the capacitor. The ALPC will automatically restart within a few milliseconds after the dip has passed.

-3dB

CFIL

16 106⋅×

loop

----------------------------------------- -

Fig.4 Automatic Laser Power Control (ALPC) loop.

a. N-substrate monitor diode. b. P-substrate monitor diode.

handbook, full pagewidth

MGR519

DC-TO-DC

CONVERTER

CFIL

DD(L)

150 mV

DC-TO-DC

CONVERTER

DD(L)

VDD − 150 mV

+ 11 hidden pages