MAX3736ETE+T Maxim Integrated Products, MAX3736ETE+T Datasheet - Page 7

• Manufacturer Part Number: MAX3736ETE+T
• Description: IC LSR DRVR 3.2GBPS 3.63V 16TQFN
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3736ETE+T

• Data Rate: 3.2Gbps
• Number Of Channels: 1
• Voltage - Supply: 2.97 V ~ 3.63 V
• Current - Supply: 22mA
• Current - Modulation: 85mA
• Current - Bias: 100mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 16-TQFN Exposed Pad
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 4. Functional Diagram
The MAX3736 laser driver consists of three operational
blocks: a bias current generator, a modulation current
generator, and a high-speed modulation path. The
laser-biasing block includes a monitor output for bias-
sensing purposes. Both the bias and modulation gener-
ating blocks are enabled and disabled by the DIS pin.
The high-speed modulation path provides a 100Ω
differential input resistance.
To maintain constant average optical power, the
MAX3736 is designed to interface to a laser controller
IC. The laser controller IC controls the MAX3736, and
maintains a constant laser power using an automatic
power-control (APC) circuit. A back-facet photodiode,
mounted in the laser package, is used to convert the
optical power into a photocurrent. The laser controller
IC adjusts the laser bias current so the monitor photodi-
ode’s current matches the level programmed by the
user. It does this by adjusting the current sourced by
the MAX3736’s BIASSET pin. The MAX3736 reacts by
increasing or decreasing the laser current at BIAS.
BC_MON
_______________________________________________________________________________________
BIAS
IN+
IN-
Detailed Description
Bias Current Generator
1.2V
50Ω
V
CC
x1
50Ω
3.2Gbps, Low-Power, Compact,
82pF
x85
BIASSET
V
CC
V
CC
1.2V
16kΩ
24kΩ
The MAX3736 features a bias current monitor
(BC_MON). This monitor is realized by mirroring a frac-
tion of the bias current and developing a voltage
across an external resistor connected to ground. For
example, connecting a 100Ω resistor to ground gives
the following relationship:
V
voltage on BC_MON must be kept below 1.39V.
The laser’s modulation amplitude can be controlled by
placing a resistor from MODSET to ground. To set the
modulation amplitude, see the I
graph in the Typical Operating Characteristics . A more
advanced control scheme employs the use of a laser
controller IC to control modulation current to
stabilize the extinction ratio. For more information on
controlling the extinction ratio, refer to Application
Note 1092: HFAN-02.3.1: Maintaining Average Power
and Extinction Ratio, Part 1, Slope Efficiency and
Threshold Current .
DIS
BC_MON
V
MODSET
CC
V
CC
7.2kΩ
= (I
x85
BIAS
SFP Laser Driver
Modulation Current Generator
MAX3736
/ 73) x 100Ω. For compliance, the
Bias Current Monitor
OUT+
OUT-
MOD
vs. R
MODSET
7