ZL40539
Dual Output CD and DVD
4 Channel Laser Diode Driver
Data Sheet
Features
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Pin compatible with EL6839
Dual output for CD/DVD laser
LVDS control signal, internal 100 ohms
Rise time 1.0 ns, Fall time 1.1 ns typical
Low noise read channel with gain of 100x to
150 mA
Channel 2 gain of 250x to 550 mA
Channel 3 gain of 150x to 500 mA
Channel 4 gain of 100x to 450 mA
Combined total output current 700 mA
On-chip oscillator with frequency and amplitude
control by external resistors
Oscillator frequency to 575 MHz, amplitude to
100 mA pk to pk
Power Up/Down control
> 2 kV ESD Single 5 V supply (±10%)
EN4
P/N ENRB
EN2
P/N
February 2005
Ordering Information
ZL40539LCG Trays/Bake/Dry Pack
ZL40539LCF Tape/Reel Bake/Dry Pack
0°C to +70°C
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32-pin QFN package
Applications
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EN3
P/N
DVD±RW/RAM
DVD±R
CD-RW
CD-R
Write optical drives
Laser Diode current switch
Supports double density DVD
Enable
INR
Chip Enable/Power
VCC_A
IN2
OUTA
GND
IN3
OUTB
IN4
VCC_B
RFA
RFB
RSA
RSB
OSCEN
SELA
Figure 1 - ZL40539 Block Diagram
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Zarlink Semiconductor Inc.
Zarlink, ZL and the Zarlink Semiconductor logo are trademarks of Zarlink Semiconductor Inc.
Copyright 2004-2005, Zarlink Semiconductor Inc. All Rights Reserved.
ZL40539
Data Sheet
Figure 2 - Pinout for 5 x 6 mm 32 pin QFN (top view)
Description
The ZL40539 is a high performance laser diode driver capable of driving two separate cathode grounded laser
diodes (e.g., 650 nm and 780 nm laser diodes).
The ZL40539 contains a 150 mA low noise read channel (ChR), and three >450 mA write channels (Ch2, Ch3 and
Ch4). Each channel amplifies the positive current supplied at its reference input (INR, IN2, IN3, IN4) by a fixed
factor of 100, 250, 150 and 100 respectively.
The device is enabled with a High level applied to the Enable Pin. The read channel is activated by applying a 'Low'
signal to the ENRB pin. Each fast write channel can be enabled by applying a positive voltage difference between
the enable pins (EN2P, EN2N), (EN3P, EN3N) and (EN4P, EN4N). The output currents of the four channels are
summed together and output as a composite signal at either OUTA (if SELA select is 'High') or OUTB (if SELA
select is 'Low'). This provides the ability to drive two different laser diodes with just one ZL40539.
Voltage control of the channel reference inputs (INR, IN2, IN3 and IN4) can be achieved by using an external
resistor in series with the reference channel input to convert a given reference potential to an input current.
An on-chip RF oscillator is provided for the reduction of laser mode hopping noise. The oscillator is enabled if
OSCEN = 'High', and its output signal is added to the appropriate current output (OUTA, if SELA select is 'High', or
OUTB, if SELA select is 'Low'). The oscillator amplitude is set by external resistors from RSA or RSB to GND. Its
frequency is set by an external resistor RFA or RFB to GND. RFA and RSA are selected when SELA = ‘High’ and
RFB and RSB when SELA = 'Low'
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Zarlink Semiconductor Inc.
ZL40539
Application Notes
Read and Write Channel Operation
Data Sheet
The device is activated by applying a 'High' signal to the Enable pin. In this mode, the read channel can be enabled
with a low signal on ENRB. The fast write channels can be enabled by applying a 'High' signal to the respective pair
of write enable pins (EN2P, EN2N), (EN3P, EN3N), or (EN4P, EN4N). The output currents of the four channels are
summed together and output as a composite signal at either OUTA (if SELA select is 'High') or OUTB (if SELA
select is 'Low'). This provides the ability to drive two different laser diodes with just one ZL40539.
Voltage control of the channel reference inputs (INR, IN2, IN3 and IN4) can be achieved quite easily using an
external resistor R
ref
in series with the reference channel input to convert a given reference potential V
ref
to an input
current, I
in
:
I
in
=
V
ref
R
ref
+
R
in
,
where R
in
is the input impedance of the respective reference channel.
On-chip RF Oscillator
An on-chip RF oscillator is enabled if OSCEN = 'High', and its output signal is added to the appropriate current
output (OUTA, if SELA select is 'High', or OUTB, if SELA select is 'Low'). The oscillator amplitude is set by an
external resistor from RSA or RSB to GND. Its frequency is set by an external resistor RFA or RFB to GND. RSA
and RFA are selected when SELA is ‘High’
The oscillator signal is summed with the programmed Write and Read levels before amplification to the output. The
oscillator signal has zero DC level and +I_pk to –I_pk signal swing. Consequently, if the programmed DC level from
the Write and Read Channels is less than the PK level programmed for the Oscillator, the combined signal will be
clipped on the negative cycle of the signal. This will increase the harmonic content of the output signal and reduce
the pk to pk amplitude output.
Thermal Considerations
Package thermal resistance is 40°C/W under the EIA/JESD51-3 compliant PCB test board condition.
Users should ensure that the junction temperature does not exceed 150°C. Thermal resistance from junction to
case and to ambient is very much dependent on how the IC is mounted onto the board, on the PCB layout and on
any heat extraction arrangements.
Power consumption and system ambient operating temperature limits should be noted and careful thermal gradient
calculations undertaken to ensure that the junction temperature never exceeds 150°C.
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Zarlink Semiconductor Inc.
ZL40539
Electrical and Optical Pulse Response
Data Sheet
ZL40539 Model
Figure 3 - Pulse Response Model
Figure 3 illustrates a simplified model of the ZL40539 output and the application. The ZL40539 consists of an ideal
switched current source and an equivalent model of the ZL40539 output stage. The Electrical Model for the Laser
Diode is a Voltage source Vd (V_on) in series with the On Resistance Rd all in parallel with the Junction
Capacitance Cd. This simplified model approximately represents the Laser Diode Electrical load when operated
beyond the Laser Threshold. To a first approximation, the Optical output is proportional to the current flow in the
Resistor Rd.
The Laser Diode and the ZL40539 are connected together buy interconnect tracks with the return current passing
through the supply decoupling bypass capacitor between ground and output Vcc.
The ZL40539 will typically switch the programmed output current in 400 ps and can be approximated to an ideal
switch with a propagation delay of Iout_on (1.2 nS). The electrical pulse response parameters, Trise, Tfall,
Overshoot and Undershoot are determined by the combined electrical network as illustrated in Figure 3.
For example, the Rise Time and Fall time for large current steps can be slew rate limited by the combined
interconnect and fixed interconnect inductance. The Fixed Inductance represents that associated with packaging
and minimum interconnect distance. The Interconnect Inductance is that associated with the additional tracking
between Laser Diode and the ZL40539 to accommodate application physical limitations. For example:-
if a pulse of 360 mA amplitude (40 mA to 400 mA) is to be switched in a time of 1 nS with the Vd =
1.6 V, then:-
the maximum volt drop across the interconnect inductance is approximately 3.5 V (maximum Vpin
for 500 mA output) – 1.6 V (Vdiode) = 1.9 V.
Consequently, L*di/dt < 1.9 V.
Hence, L < 1.9/ (0.36A/1nS) = 5.3 nH.
Small current step size Rise and Fall time will be determined by the Bandwidth of the combined network. This is
dominated by the Interconnect Inductance and the output Capacitance. Similarly, the overshoot and undershoot will
be determined by the Q of the network. This is a function of the Source Impedance from the ZL40539, the
Interconnect inductance and the Load impedance of the Laser Diode. Figure 3 includes example simplified
estimates of the Q and BW of the combined Laser Diode, ZL40539 and interconnect network for two different
interconnect inductance values (5 nH & 7 nH) and two different Diode On resistance (3 Ohm & 7 Ohm). This simple
analysis illustrates the change in BW and Q of the network depending on these parameters. This in turn effects the
Rise Time and Fall time and the Overshoot and Undershoot performance achieved in the application.
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Zarlink Semiconductor Inc.
ZL40539
Data Sheet
Specified Electrical Performance with 15 mm Interconnect and Zarlink ZLE40539 Evaluation Board
The specified transient pulse performance in the table are results based on the electrical measurements and
simulations across full process corners using the Zarlink Evaluation Board using a 3.9 Ohm resistive load to
ground.
The track interconnect between ZL40539 and the 3.9 Ohm Resistor is 15 mm long and uses a 2 mm wide track on
single sided FR4 board. The return path is via two 2 mm wide tracks spaced 0.25 mm either side of the track
between output and the 3.9 ohm resistor. The combined forward and return path forms a co planar transmission
line with a characteristic impedance of approximately 120 ohms.
The tight coupled return paths carrying the return current reduce the effective series inductance (Leff) which can be
approximated to:-
Leff = 2 * Lint * (1 - K) + 2 * Lfix * (1 - K).
The ZLE40539 board has two positions for the Laser Diode at two different distances. (15 and 30 mm).
The measured value of Leff is 7 nH.
The estimated value of Leff = 2 * 8 (1 – 0.5) = 8 nH.
The actual pulse response achieved in an application is thus dependent on the application.
Application Layout Guide Lines
Minimize Interconnect Inductance by:
1. Using Short Interconnect Distance
2. Use wide interconnect tracks
3. Keep the return path tightly coupled to the forward path
ZL40539E Interconnect
Figure 4 - ZLE40539 Application Board Electrical Interconnect
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