MAX3668EHJ+ Maxim Integrated Products, MAX3668EHJ+ Datasheet - Page 9

• Manufacturer Part Number: MAX3668EHJ+
• Description: IC LSR DRVR 622MBPS 3.63V 32TQFP
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3668EHJ+

• Data Rate: 622Mbps
• Number Of Channels: 1
• Voltage - Supply: 3.14 V ~ 5.5 V
• Current - Supply: 38mA
• Current - Modulation: 75mA
• Current - Bias: 80mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-TQFP, 32-VQFP
• Mounting Type: Surface Mount
• Package: 32TQFP
• Number Of Channels Per Chip: 1
• Operating Supply Voltage: 3.14 to 5.5 V
• Supply Current: 38 mA
• Maximum Power Dissipation: 929 mW
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

ratio is r
-40°C to +85°C, and the laser diode has the following
characteristics:
The desired monitor diode current is estimated by
I
vs. APC Set Resistor graph in the Typical Operating
Characteristics shows that R
To achieve a minimum extinction ratio (r
temperature and lifetime, calculate the required extinc-
tion ratio at +25°C. Assuming r
optical power P
required modulation current is 1.81(mW) / 0.05(mW/mA)
= 36.2mA. The Modulation Current vs. Modulation Set
Resistor graph in the (see Typical Operating Characteri-
stics) shows that R
Calculate the maximum threshold current (I
T
50mA, the maximum bias current should be:
In this example, I
Maximum Bias Set Resistor graph in the Typical
Operating Characteristics shows that R
be 3kΩ.
To drive modulation currents greater than 50mA at
3.3V, external pull-up inductors (Figure 5) should be
used to DC-bias the modulation output at V
configuration isolates the laser forward voltage from the
output circuitry and allows the output at OUT+ to swing
above and below the supply voltage V
At +5V power supply, the headroom voltage for the
MAX3668 is significantly improved. In this case, it is
possible to achieve a modulation current of more than
50mA (using resistor pull-ups as shown in the Typical
Operating Circuit). The MAX3668 can also be DC-coupled
to a laser diode when operating at +5V supply; the volt-
age at OUT+ should be ≥ 2.0V for proper operation.
MD
A
Threshold Temperature
Coefficient:
Laser to Monitor Transfer:
Wavelength:
Threshold Current:
Laser Slope Efficiency:
= +85°C and end of life. Assuming I
= P
AVE
e
Modulation Current More than 50mA
= 6.6 (8.2dB), the operating temperature is
Laser Driver with Automatic Power Control
×
ρ
I
BIAS
MON
p-p
BIAS
MODSET
_______________________________________________________________________________________
= 1.81mW according to Table 1. The
= I
= 200µA. The Monitor Diode Current
TH(MAX)
= 68.1mA. The Bias Current vs.
should be 5kΩ.
APCSET
Determine R
Determine R
Determine R
e
+ I
λ = 1.3µm
Ι
β
ρ
η = 0.05mW/mA
at +25°C
= 20, the peak-to-peak
TH
TH
MON
MOD
should be 6kΩ.
= 22mA at +25°C
= 1.3%/°C
CC
= 0.2A/W
/ 2
BIASMAX
.
e
) of 6.6 over
TH(MAX)
CC
TH(MAX)
BIASMAX
MODSET
APCSET
. Such a
+3.3V, 622Mbps SDH/SONET
should
) at
=
For high current density and reliable operation, the
MAX3668 uses gold metalization. Make connections to
the die with gold wire only, using ball-bonding tech-
niques. Wedge bonding is not recommended. Die-pad
size is 4 mils (100µm) square, and die thickness is 12
mils (300µm) mils.
To minimize inductance, keep the connections between
the MAX3668 output pins and LD as close as possible.
Optimize the laser diode performance by placing a
bypass capacitor as close as possible to the laser
anode. Use good high-frequency layout techniques
and multilayer boards with uninterrupted ground planes
to minimize EMI and crosstalk.
Using the MAX3668 laser driver alone does not ensure
that a transmitter design is compliant with IEC 825. The
entire transmitter circuit and component selections must
be considered. Customers must determine the level of
fault tolerance required by their application, recognizing
that Maxim products are not designed or authorized for
use as components in systems intended for surgical
implant into the body, for applications intended to sup-
port or sustain life, or for any other application where the
failure of a Maxim product could create a situation
where personal injury or death may occur.
Figure 5. Output Termination for Maximum Modulation Current
MAX3668
OUT+
OUT-
BIAS
MD
10Ω
V
CC
Laser Safety and IEC 825
FERRITE BEAD
Layout Considerations
FERRITE
BEADS
1.0µF
C
D
Wire Bonding Die
5Ω
R
D
1000pF
LD
R
FILT
C
FILT
9