MAX3286 Datasheet, PDF (11/28 Pages) Maxim Integrated Products – 3.0V to 5.5V, 1.25Gbps/2.5Gbps LAN Laser Drivers

3.0V to 5.5V, 1.25Gbps/2.5Gbps
LAN Laser Drivers
force a shutdown if a fault is detected. The shutdown
condition is latched until reset by a toggle of EN, EN, or
power.
Another safety system, open fiber control (OFC), uses
safety interlocks to prevent eye hazards. To accommo-
date the OFC standard, the MAX3286/MAX3296 series
provide dual enable inputs and dual fault outputs.
The safety circuitry contains fault detection, dual enable
inputs, latched fault outputs, and a pulse generator
(Figure 6).
Safety circuitry monitors the APC circuit to detect unsafe
levels of laser emission during single-point failures. A
single-point failure can be a short to V_CC or GND or a
short between any two IC pins.
1.3
1.2
R_TC ≥ 1.9kΩ
R_MOD = OPEN
TEMPCO = 4000ppm/°C
1.1
1.0
0.9
R_TC = OPEN
TEMPCO = 50ppm/°C
0.8
0.7
0.6
0 10 20 30 40 50 60 70 80 90 100 110
JUNCTION TEMPERATURE (°C)
Figure 5. Modulation Current vs. Temperature for Maximum
and Minimum Temperature Coefficient
Pulse Generator
During startup, the laser does not emit light and the
APC loop is not closed, triggering a fault signal. To
allow startup, an internal fault-delay pulse disables the
safety system for a programmable period of time, allowing
the driver to begin operation. The length of the pulse is
determined by the capacitor connected at FLTDLY and
should be set 5 to 10 times longer than the APC time
constant. The internal safety features can be disabled
by connecting FLTDLY to GND. Note that EN must be
high, EN must be low, and V_CC must be in the opera-
tional range for laser operation.
Fault Detection
The MAX3286/MAX3296 series has extensive and com-
prehensive fault-detection features. All critical nodes
are monitored for safety faults, and any node voltage
that differs significantly from its expected value results
in a fault (Table 1). When a fault condition is detected,
the laser is shut down. See the Applications Information
section for more information on laser safety.
Shutdown
The laser drivers offer dual redundant bias shutdown
mechanisms. The SHDNDRV output drives an optional
external MOSFET semiconductor. The bias and modu-
lation drivers have separate internal disable signals.
Latched Fault Output
Two complementary FAULT outputs are provided with
the MAX3286/MAX3296 series. In the event of a fault,
these outputs latch until one of three events occurs:
1) The power is switched off, then on.
EN
V_CC
EN
(FROM POR CIRCUIT)
FAULT
DETECTION
REF_FAULT
MONITOR_FAULT
MD_FAULT
POLARITY_FAULT
TC_FAULT
MOD_FAULT
PULSE GENERATOR
t_FLTDLY
R
Q
RESET
DOMINANT
FAULT
LATCH
S
ENABLE
MAX3286
MAX3296
FLTDLY
FAULT
FAULT
SHDNDRV
Figure 6. Simplified Safety Circuit Schematic
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