MAX3736 Maxim Integrated Products, MAX3736 Datasheet - Page 9

• Manufacturer Part Number: MAX3736
• Description: SFP Laser Driver
• Manufacturer: Maxim Integrated Products

The MAX3736 data inputs are SFP MSA compliant. On-
chip 100Ω, differential input impedance is provided for
optimal termination (Figure 5). Because of the on-chip
biasing network, the MAX3736 inputs self-bias to the
proper operating point to accommodate AC-coupling.
The MAX3736 is directly compatible with +3.3V reference
CML. Either DC or AC-coupling can be used for CML ref-
erenced to +3.3V. For all other logic types, AC-coupling
should be used. DC coupling to CML is fine, but it
negates the squelching function on the modulation path.
For applications requiring a modulation current greater
than 60mA, headroom is insufficient for proper operation
of the laser driver if the laser is DC-coupled. To avoid
this problem, the MAX3736 modulation 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
ward voltage from the output circuitry and allows the out-
put at OUT+ to swing above and below the supply
voltage (V
Figure 5. Simplified Input Circuit Schematic
IN+
IN-
0.11pF
0.11pF
Modulation Currents Exceeding 60mA
MAX3736
CC
CC
). When AC-coupled, the MAX3736 modula-
PACKAGE
Input Termination Requirements
. Such a configuration isolates laser for-
0.65nH
0.65nH
Applications Information
_______________________________________________________________________________________
V
V
CC
CC
50Ω
50Ω
Data Input Logic Levels
82pF
16kΩ
24kΩ
V
CC
3.2Gbps, Low-Power, Compact,
tion current can be programmed from 5mA to 85mA.
Refer to Maxim Application Note HFAN 02.0: Interfacing
Maxim’s Laser Drivers to Laser Diodes for more informa-
tion on AC-coupling laser drivers to laser diodes.
Figures 5 and 6 show simplified input and output cir-
cuits for the MAX3736 laser driver. If dice are used,
replace package parasitic elements with bondwire par-
asitic elements.
The MAX3736 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 mils (2388µm) square, and die thickness is 15 mils
(381µm). Refer to Maxim Application Note HFAN-
08.0.1: Understanding Bonding Coordinates and
Physical Die Size for additional information.
To minimize loss and crosstalk, keep the connections
between the MAX3736 output and the laser as short as
possible. Use good high-frequency layout techniques
and multilayer boards with an uninterrupted ground
plane to minimize EMI and crosstalk.
Figure 6. Simplified Output Circuit Schematic
MAX3736
SFP Laser Driver
V
Layout Considerations
CC
Wire-Bonding Die
Interface Models
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0.43nH
0.43nH
PACKAGE
0.11pF
0.11pF
OUT+
OUT-
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