Datasheet

Determine R
BIASMAX
Calculate the maximum threshold current (I
TH(MAX)
) at
T
A
= +85°C and end of life. Assuming I
TH(MAX)
=
50mA, the maximum bias current should be:
I
BIASMAX
= I
TH(MAX)
+ I
MOD
/2
In this example, I
BIASMAX
= 68.1mA. The I
BIASMAX
vs.
R
BIASMAX
graph in the Typical Operating Characteristics
shows that R
BIASMAX
should be 3.2kΩ.
Modulation Currents Exceeding 60mA
With a +5V power supply, the headroom voltage for the
MAX3869 is significantly improved. In this case, it is
possible to achieve a modulation current of more than
60mA with AC-coupling, if the junction temperature is
kept below 150°C. The MAX3869 can also be DC-cou-
pled to a laser diode when operating with a +5V sup-
ply; the voltage at OUT+ should be ≥2.0V for proper
operation.
Wire Bonding Die
For high current density and reliable operation, the
MAX3869 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) square.
Layout Considerations
To minimize inductance, keep the connections between
the MAX3869 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.
Laser Safety and IEC 825
Using the MAX3869 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. Each customer must determine the level
of fault tolerance required by their application, recogniz-
ing 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.
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
______________________________________________________________________________________ 11
Chip Information
TRANSISTOR COUNT: 1561
SUBSTRATE CONNECTED TO GND