MAX3766 Datasheet, PDF (8/20 Pages) Maxim Integrated Products – 622Mbps LAN/WAN Laser Driver with Automatic Power Control and Safety Shutdown

622Mbps LAN/WAN Laser Driver with
Automatic Power Control and Safety Shutdown
5.1k
V_CC
R_MOD
FAIL
MOD
REF2
R_TC
TC
REF1
V_CC V_CC
520Ω
REFERENCE
GENERATOR
2k
V
TEMP
SAFETY
ENABLE
SAFETY
START-UP
CIRCUIT
SHDN
FAILURE
FAILURE
DETECTION
MAX3766
R_POWERSET
R_BIASMAX
BIASMAX
POWERSET
BANDGAP
520Ω
300Ω
C_MD
V
TEMP
POWERSET
MIRROR
1X
APC
I_APC
MONITOR-
DIODE
AMPLIFIER
MD
V_CC
MONITOR
PHOTODIODE
V_CC - 2V
AUTOMATIC
POWER CONTROL
LASER
BIAS
V_CC
IN+
IN-
PECL
INPUT
BUFFER
SHDN
MODULATION
MIRROR
30X
MODULATION-
CURRENT
DRIVER
BIAS
MIRROR
40X
LASER BIAS CIRCUIT
OUT+
OUT-
V_CC
GNDOUT
VCCOUT
Figure 2. Functional Diagram
The available laser bias current is programmed by
connecting external resistor R_BIASMAX from REF1 to
BIASMAX. The BIASMAX programming current is
adjusted by the APC circuit and amplified by the laser
bias circuit.
An internal 520Ω resistor between BIASMAX and the
mirror input at internal node APC limits the maximum
laser bias current when BIASMAX is connected directly
to REF1. BIASMAX can be directly connected to REF1
in space-constrained designs, causing the maximum
programming current (about 2.5mA) to flow into
BIASMAX. Selecting a BIASMAX resistor saves power
and limits the transmitter’s maximum light output.
R_BIASMAX can be estimated as follows:
( ) ^{1.55V 40}
R_BIASMAX =
− 520Ω
I _BIASMAX
This equation applies to maximum bias currents above
10mA.
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