MAX3669EHJ+ Maxim Integrated Products, MAX3669EHJ+ Datasheet - Page 7

• Manufacturer Part Number: MAX3669EHJ+
• Description: IC LASR DRVR 622MBPS 5.5V 32TQFP
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3669EHJ+

• Data Rate: 622Mbps
• Number Of Channels: 1
• Voltage - Supply: 3.14 V ~ 5.5 V
• Current - Supply: 40mA
• Current - Modulation: 75mA
• Current - Bias: 80mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-TQFP, 32-VQFP
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

The MAX3669 laser driver consists of three main parts:
a high-speed modulation driver, a laser-biasing block
with automatic power control (APC), and bias current
and modulation current monitors. The circuit is opti-
mized for low-voltage (+3.3V) operation.
The output stage is composed of a high-speed differential
pair and a programmable modulation current source.
Since the modulation output drives a maximum current
of 75mA into the laser with a 230ps edge speed, large
transient voltage spikes can be generated due to the
parasitic inductance. These transients and the laser for-
ward voltage leave insufficient headroom for the proper
operation of the laser driver if the modulation output is
DC-coupled to the laser diode. To solve this problem,
the MAX3669’s modulation output is designed to be
Figure 3. Functional Diagram
Laser Driver with Current Monitors and APC
V
V
CC
CC
R
R
_______________________________________________________________________________________
BIASMON
MODMON
ENABLE
DATA+
DATA-
Detailed Description
I
I
MOD
BIAS
38
29
MAX3669
V
CC
100kΩ
MODSET
R
MODSET
+3.3V, 622Mbps SDH/SONET
R
BIASMAX
165X
BIASMAX
AC-coupled to the cathode of a laser diode. A simpli-
fied functional diagram is shown in Figure 3.
The MAX3669 modulation output is optimized for driv-
ing a 20Ω⎥⎥ 10Ω load; the minimum required voltage at
OUT+ is 2.0V. Modulation current swings of 75mA are
possible. To interface with the laser diode, a damping
resistor (R
RC shunt network may be used to compensate for the
laser-diode parasitic inductance, thereby improving the
optical output aberrations and duty-cycle distortion.
At a 622Mbps data rate, any capacitive load at the cath-
ode of a laser diode degrades the optical output perfor-
mance. Since the BIAS output is directly connected to the
laser cathode, minimize the parasitic capacitance associ-
ated with this pin by using an inductor to isolate the BIAS
pin from the laser diode.
FAIL
5X
DETECTOR
FAILURE
40X
D
) is required for impedance matching. An
I
MOD
C
APC
CAPC
I
MD
APCSET
R
APCSET
I
BIAS
BIAS
MD
OUT+
OUT-
7