MAX3735AETG+ Maxim Integrated Products, MAX3735AETG+ Datasheet - Page 14

• Manufacturer Part Number: MAX3735AETG+
• Description: IC LSR DRVR 2.7GBPS 3.63V 24TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3735AETG+

• Data Rate: 2.7Gbps
• Number Of Channels: 1
• Voltage - Supply: 2.97 V ~ 3.63 V
• Current - Supply: 27mA
• Current - Modulation: 85mA
• Current - Bias: 100mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 24-TQFN Exposed Pad
• Mounting Type: Surface Mount
• Operating Supply Voltage: 3.3 V
• Supply Current: 27 mA
• Maximum Operating Temperature: + 85 C
• Maximum Power Dissipation: 1354 mW
• Minimum Operating Temperature: - 40 C
• Mounting Style: SMD/SMT
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Capacitors Used with MAX3735/MAX3735A SFP Module
Designs for more information on choosing C
and AC-coupled laser interfaces.
Use the following equation to find the C
using the MAX3735:
where units are:
C
then be chosen as approximately 20x smaller than C
for the MAX3735.
Use Table 4 to choose C
C
the lasers (generally at cold temperature). C
tion assumes a 34% reduction in the gain of the lasers at
+85°C from the cold (-40°C) values.
Table 4. MAX3735A CAPC Selection
where Gain = I
pled lasers. C
4x to 20x smaller than C
For more information on using the MAX3735/MAX3735A
with the Dallas DS1858/DS1859 SFP controller, refer to
Maxim Application Note HFAN 2.3.3: Optimizing the
Resolution of Laser Driver Setting Using Linear Digital
Potentiometers for more information.
For applications requiring a modulation current greater
than 60mA, headroom is insufficient for proper opera-
tion of the laser driver if the laser is DC-coupled. To
avoid this problem, the MAX3735/MAX3735A’s modula-
tion output can be AC-coupled to the cathode of a laser
diode. An external pullup inductor is necessary to DC-
bias the modulation output at V
2.7Gbps, Low-Power SFP Laser Drivers
14
C
APC
APC
APC
0.22 I
______________________________________________________________________________________
LASER GAIN (A/A)
in µF, I
should be chosen according to the highest gain of
= 4.04 × 10
Modulation Currents Exceeding 60mA
TH
2
) × (1947 + 833 I
0.005
0.007
0.010
0.020
0.030
0.040
TH
MD
MD
, and I
Using the MAX3735/MAX3735A
/(I
can then be chosen as approximately
-9
BIAS
× t
with Digital Potentiometers
MOD
_on
APC
APC
I
- I
MOD
× η × ρ
in mA and t
TH
MOD
for the MAX3735A
when using the MAX3735A.
3
+ 0.5 x I
)
CC
- 7.78 I
MON
. Such a configuration
ON
C
(29.3 + 20.6 I
MOD
APC
APC
0.039
0.047
0.068
0.100
0.120
0.120
MOD
in µs. C
) for DC-cou-
(µF)
APC
MAX3735A
value when
2
APC
MAX3735
+ 0.103
for DC-
MD
selec-
TH
APC
can
-
isolates laser forward voltage from the output circuitry
and allows the output at OUT+ to swing above and
below the supply voltage (V
MAX3735/MAX3735A modulation current can be pro-
grammed from 10mA to 85mA. Refer to Maxim
Application Note HFAN 02.0: Interfacing Maxim’s Laser
Drivers to Laser Diodes for more information on AC-
coupling laser drivers to laser diodes.
Figures 6 and 7 show simplified input and output cir-
cuits for the MAX3735/MAX3735A laser driver. If dice
are used, replace package parasitic elements with
bondwire parasitic elements.
The MAX3735 uses gold metalization with a thickness of
5µm (typ). Maxim characterized this circuit with gold wire
ball bonding (1-mil diameter wire). Die-pad size is 94 mil
(2388µm) square, and die thickness is 15 mil (381µm).
Refer to Maxim Application Note HFAN-08.0.1:
Understanding Bonding Coordinates and Physical Die
Size for additional information.
To minimize inductance, keep the connections between
the MAX3735 output pins and laser diode 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 tech-
niques and multiple-layer boards with uninterrupted
ground planes to minimize EMI and crosstalk.
The exposed pad on the 24-pin QFN provides a very
low thermal resistance path for heat removal from the IC.
The pad is also electrical ground on the MAX3735/
MAX3735A and must be soldered to the circuit board
ground for proper thermal and electrical performance.
Refer to Maxim Application Note HFAN-08.1: Thermal
Considerations for QFN and Other Exposed-Pad
Packages for additional information.
Using the MAX3735/MAX3735A laser driver alone does
not ensure that a transmitter design is compliant with IEC
825. The entire transmitter circuit and component selec-
tions must be considered. Each user must determine the
level of fault tolerance required by the application, recog-
nizing that Maxim products are neither designed nor
authorized for use as components in systems intended
for surgical implant into the body, for applications intend-
ed to support or sustain life, or for any other application
in which the failure of a Maxim product could create a
situation where personal injury or death may occur.
Laser Safety and IEC 825
Layout Considerations
Exposed-Pad Package
CC
). When AC-coupled, the
Wire Bonding Die
Interface Models