MAX3996CGP Maxim Integrated Products, MAX3996CGP Datasheet - Page 13

• 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

The compensation components (R
easily determined by experimentation. For interfacing
with edge-emitting lasers, refer to application note
HFAN-2.0, Interfacing Maxim Laser Drivers with Laser
Diodes. Begin with R
C
(Figure 12).
Figure 12. Laser Compensation
To achieve single-point fault tolerance, Maxim recom-
mends an external shutdown transistor (Figure 11). In
the event of a fault, SHDNDRV asserts high, placing the
shutdown transistor in cutoff mode and thereby shutting
off the bias current.
The International Electrotechnical Commission (IEC)
determines standards for hazardous light emissions
from fiber optic transmitters. IEC 825 defines the maxi-
mum light output for various hazard levels. The
MAX3996 provides features that facilitate compliance
with IEC825. A common safety precaution is single-
point fault tolerance, whereby one unplanned short,
open, or resistive connection does not cause excess
light output. When this laser driver is used, as shown in
the Typical Application Circuit, the circuits respond to
faults as listed in Table 3. Using this laser driver alone
does not ensure that a transmitter design is compliant
with IEC825. The entire transmitter circuit and compo-
nent selections must be considered. Customers must
determine the level of fault tolerance required by their
applications, recognizing that Maxim products are not
designed or authorized for use as components in sys-
tems intended for surgical implant into the body, for
applications intended to support or sustain life, or for
any other application where the failure of a Maxim
F
until the desired transmitter response is obtained
Applications Information
______________________________________________________________________________________
F
CORRECTLY COMPENSATED
Using External Shutdown
= 50Ω and C
Laser Safety and IEC825
UNCOMPENSATED
OVERCOMPENSATED
TIME
F
F
and C
= 2pF. Increase
F
) are most
3.0V to 5.5V, 2.5Gbps VCSEL
product could create a situation where personal injury
or death may occur.
The MAX3996 is a high-frequency product whose per-
formance largely depends upon the circuit board layout.
Use a multilayer circuit board with a dedicated ground
plane. Use short laser-package leads placed close to
the modulator outputs. Power supplies must be capaci-
tively bypassed to the ground plane, with surface-mount
capacitors placed near the power-supply pins.
The dominant pole of the APC circuit normally is at
COMP. To prevent a second pole in the APC that can
lead to oscillations, ensure that parasitic capacitance at
MD is minimized (10pF).
Laser output is ringing or contains overshoot. Induc-
tive laser packaging often causes this. Try reducing the
length of the laser leads. Modify the filter components to
reduce the driver’s output edge speed (see the Design
Procedure section). Extreme ringing can be caused by
low voltage at the OUT± pins. This might indicate that
pullup beads or a lower modulation current are needed.
Low-frequency oscillation on the laser output. This
is more prevalent at low temperatures. The APC might
be oscillating. Try increasing the value of C
add additional degeneration by placing some resis-
tance from MON1 to GND. Ensure that the parasitic
capacitance at the MD node is kept very small (<10pF).
The APC is not needed. Connect BIAS to V
MD open, and connect MON2 and COMP to ground.
The modulator is not needed. Leave TC and MODSET
open. Connect IN+ to V
750Ω, and leave OUT+ and OUT- open.
Figures 13–17 show typical models for the inputs and
outputs of the MAX3996, including package parasitics.
Figure 13. FAULT Output
NOTE: THE FAULT PIN IS AN OPEN-COLLECTOR OUTPUT
and Laser Driver
MAX3996
Layout Considerations
CC
4kΩ
, IN- to ground through
Common Questions
Interface Models
FAULT
CC
COMP
, leave
13
or