Datasheet

MAX3766
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:
This equation applies to maximum bias currents above
10mA.
R =
1.55V 40
I
520
BIASMAX
BIASMAX
()
−Ω
622Mbps LAN/WAN Laser Driver with
Automatic Power Control and Safety Shutdown
8 _______________________________________________________________________________________
SAFETY
START-UP
CIRCUIT
FAILURE
DETECTION
REFERENCE
GENERATOR
2k
V
V
TEMP
BANDGAP
POWERSET
MIRROR
1X
AUTOMATIC
POWER CONTROL
V
CC
- 2V
MONITOR-
DIODE
AMPLIFIER
LASER BIAS CIRCUIT
BIAS
MIRROR
40X
APC
I
LBP
I
BIASMAX
I
APC
TEMP
MODULATION
MIRROR
30X
PECL
INPUT
BUFFER
ENABLE
SHDN
SAFETY
V
CC
V
CC
FAIL MOD REF2 TC REF1 BIASMAX
C
MD
V
CC
V
CC
V
CC
MONITOR
PHOTODIODE
LASER
MD
BIAS
OUT+
OUT-
POWERSET
R
POWERSET
R
BIASMAX
R
TC
R
MOD
5.1k
520
Ω
520
Ω
300
Ω
FAILURE
SHDN
GNDOUT VCCOUT
V
CC
IN+
IN-
MODULATION-
CURRENT
DRIVER
MAX3766
Figure 2. Functional Diagram