1.0625Gbps to 11.3Gbps, SFP+ Laser Driver
with Laser Impedance Mismatch Tolerance
Figure 6. Simplified I/O Structures
The data inputs and outputs are the most critical paths
for the device and great care should be taken to mini-
mize discontinuities on these transmission lines between
the connector and the IC. Here are some suggestions for
maximizing the performance of the IC:
• The data inputs should be wired directly between the
cable connector and IC without stubs.
• The data transmission lines to the laser should be kept
as short as possible and be designed for 50I differ-
ential or 25I single-ended characteristic impedance.
• An uninterrupted ground plane should be positioned
beneath the high-speed I/Os.
• Ground path vias should be placed close to the IC and
the input/output interfaces to allow a return current
path to the IC and the laser.
• Maintain 100I differential transmission line imped-
ance into the IC.
• Use good high-frequency layout techniques and mul-
tilayer boards with an uninterrupted ground plane to
minimize EMI and crosstalk.
Refer to the schematic and board layers of the MAX3946
Evaluation Kit (MAX3946EVKIT) for more information.
Exposed-Pad Package and
The exposed pad on the 24-pin TQFN provides a very
low-thermal resistance path for heat removal from the IC.
The pad is also electrical ground on the IC and must be
soldered to the circuit board ground for proper thermal
and electrical performance. Refer to Application Note 862:
HFAN-08.1: Thermal Considerations of QFN and Other
Exposed-Paddle Packages for additional information.