MAX3996CGP Maxim Integrated Products, MAX3996CGP Datasheet - Page 7

• Manufacturer Part Number: MAX3996CGP
• Description: Laser Driver +3.0V to +5.5V, 2.5G bps VCSEL and Laser
• Manufacturer: Maxim Integrated Products

Specifications of MAX3996CGP

• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

Figure 1. Output Load for AC Specification
The MAX3996 contains a bias generator with automatic
power control and smooth start, a laser modulator, a
power-on reset (POR) circuit, and safety circuitry
(Figure 3).
Figure 3. Laser Driver Functional Diagram
V
TX_DISABLE
ID
PORDLY
IN+
IN-
*MURATA
BLM11HA102SG
0.01µF
0.01µF
POR CIRCUIT
IN+
IN-
100Ω
MODULATION
MODULATION
V
MAX3996
CC
ENABLE
FAULT
3.0V TO 5.5V
R
INPUT BUFFER
MODULATION CURRENT
IN
V
TC
CC
MAX3996
GENERATOR
_______________________________________________________________________________________
FAULT
I
CC
CIRCUITRY
SAFETY
Detailed Description
MODULATION CURRENT
MODSET
TC
SHDNDRV
MODULATION
R
R
OUT
MOD
LASER
GENERATOR
BIAS ENABLE
V
CC
50Ω
MODSET
R
OUT
WITH SMOOTH
OUT-
OUT+
0.01µF
GENERATOR
V
CC
25Ω
START
BIAS
50Ω
3.0V to 5.5V, 2.5Gbps VCSEL
i
OUT
FERRITE
BEAD*
25Ω
OUT-
OUT+
BIAS
MD
COMP
MON1
MON2
0.01µF
i
MOD
Figure 4 shows the bias generator circuitry that con-
tains a power-control amplifier, smooth-start circuitry,
and two bias-fault sensors. The power-control amplifier
combined with an internal NPN transistor provides DC
laser current to bias the laser in a light-emitting state.
The APC circuitry adjusts the laser bias current to main-
tain average power over temperature and changing
laser properties. The smooth-start circuitry prevents
current spikes to the laser during power-up or enable,
ensuring compliance with safety requirements and
extending the life of the laser.
The MD input is connected to the anode of a monitor
diode, which is used to sense laser power. The BIAS
output is connected to the cathode of the laser through
an inductor or ferrite bead. The power-control amplifier
drives a transistor to control the laser’s bias current. In
a fault condition (Table 1), the base of the bias-driving
transistor is pulled low to ensure that bias current is
turned off.
Figure 2. Required Input Signal and Modulation-Current Polarity
Figure 4. Bias Circuitry
V
ID
MD
= V
CURRENT
IN+
SMOOTH START
VOLTS
- V
i
MOD
V
V
MAX3996
IN+
IN-
IN-
POWER-CONTROL
1.1V
AMPLIFIER
and Laser Driver
SINGLE-ENDED SIGNAL
DIFFERENTIAL SIGNAL
DISABLE
BIAS
TIME
COMP
FAULT 1
FAULT 2
BIAS
BIAS
Bias Generator
400mV
400mV
R
100mV
1100mV
MON
200mV
2200mV
(11Ω)
P-P
P-P
P-P
P-P
MIN
MIN
BIAS
MON2
MON1
MAX
MAX
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