MAX3869EHJ+T Maxim Integrated Products, MAX3869EHJ+T Datasheet - Page 9

• Manufacturer Part Number: MAX3869EHJ+T
• Description: IC LASER DRIVR 2CHAN 5.5V 32TQFP
• Manufacturer: Maxim Integrated Products
• Type: Laser Diode Driver (Fiber Optic)r

Specifications of MAX3869EHJ+T

• Data Rate: 2.5Gbps
• Number Of Channels: 2
• Voltage - Supply: 3.14 V ~ 5.5 V
• Current - Supply: 64mA
• Current - Modulation: 60mA
• Current - Bias: 100mA
• Operating Temperature: -40°C ~ 85°C
• Package / Case: 32-TFQFP, Exposed Pad
• Mounting Type: Surface Mount
• Lead Free Status / RoHS Status: Lead free / RoHS Compliant

To minimize input data pattern-dependent jitter, the dif-
ferential clock signal should be connected to the data
input latch, which is selected by an external LATCH
control. If LATCH is high, the input data is retimed by
the rising edge of CLK+. If LATCH is low, the input data
is directly connected to the output stage. When this
latch function is not used, connect CLK+ to V
leave CLK- unconnected.
The MAX3869 incorporates a laser driver enable func-
tion. When ENABLE is low, both the bias and modulation
currents are off. The typical laser enable time is 250ns,
and the typical disable time is 25ns.
The MAX3869 features bias- and modulation-current
monitor outputs. The BIASMON output sinks a current
equal to 1/37 of the laser bias current (I
MODMON output sinks a current equal to 1/29 of the
laser modulation current (I
MODMON should be connected through a pull-up resis-
tor to V
voltage at BIASMON greater than V
age at MODMON greater than V
For laser safety reasons, the MAX3869 incorporates a
slow-start circuit that provides a delay of 250ns for
enabling a laser diode.
The MAX3869 provides an APC failure monitor
(TTL/CMOS) to indicate an APC loop tracking failure.
FAIL is set low when the APC loop can no longer adjust
the bias current to maintain the desired monitor current.
The MAX3869 provides short-circuit protection for the
modulation, bias, and monitor current sources. If either
BIASMAX, MODSET, or APCSET is shorted to ground,
the bias and modulation output will be turned off.
When designing a laser transmitter, the optical output is
usually expressed in terms of average power and extinc-
tion ratio. Table 1 gives the relationships that are helpful
in converting between the optical average power and the
modulation current. These relationships are valid if the
mark density and duty cycle of the optical waveform are
50%.
CC
. Choose a pull-up resistor value that ensures a
_______________________________________________________________________________________
+3.3V, 2.5Gbps SDH/SONET Laser Driver
Optional Data Input Latch
Short-Circuit Protection
Design Procedure
MOD
APC Failure Monitor
CC
Current Monitors
/ 29). BIASMON and
- 1.0V.
CC
Enable Control
- 1.6V and a volt-
BIAS
with Current Monitors and APC
Slow-Start
/ 37). The
CC
and
For a given laser power P
extinction ration (r
culated using Table 1. See the I
in the Typical Operating Characteristics and select the
value of R
rent at +25°C.
When using the MAX3869 in open-loop operation, the
bias current is determined by the R
select this resistor, determine the required bias current
at +25°C. See the I
Typical Operating Characteristics and select the value
of R
+25°C.
When using the MAX3869 in closed-loop operation, the
R
able to the laser diode over temperature and life. The
APC loop can subtract from this maximum value but
cannot add to it. See the I
in the Typical Operating Characteristics and select the
value of R
bias current at +85°C.
When the MAX3869’s APC feature is used, program the
average optical power by adjusting the APCSET resistor.
To select this resistor, determine the desired monitor cur-
rent to be maintained over temperature and life. See the
I
Characteristics and select the value of R
responds to the required current.
To minimize optical output aberrations caused by signal
reflections at the electrical interface to the laser diode, a
series damping resistor (R
Additionally, the MAX3869 outputs are optimized for a
25Ω load. Therefore, the series combination of R
R
Table 1. Optical Power Definition
MD
Average Power
Extinction Ratio
Optical Power High
Optical Power Low
Optical Amplitude
Laser Slope
Efficiency
Modulation Current
BIASMAX
L
PARAMETER
(where R
BIASMAX
vs. R
Programming the Modulation Current
MODSET
resistor sets the maximum bias current avail-
BIASMAX
APCSET
that corresponds to the required current at
L
represents the laser-diode resistance)
Programming the Bias Current
Interfacing with Laser Diodes
e)
that corresponds to the required cur-
SYMBOL
, the modulation current can be cal-
BIASMAX
that corresponds to the end-of-life
Programming the APC Loop
graph in the Typical Operating
P
I
Pp-p
MOD
AVG
P
P
r
η
e
1
0
AVG
BIASMAX
P
r
P
P
Pp-p = 2P
I
D
vs. R
η = Pp-p / I
MOD
e
AVG
1
0
, slope efficiency (η), and
) is required (Figure 4).
= P
= 2P
= 2P
MOD
= Pp-p / η
= (P
1
BIASMAX
/ P
AVG
AVG
BIASMAX
vs. R
vs. R
RELATION
0
0
AVG
MOD
+ P
·
/ (r
APCSET
r
BIASMAX
e
MODSET
e
(r
1
/ (r
) / 2
e
+ 1)
graph in the
- 1) / (r
resistor. To
e
+ 1)
that cor-
D
graph
graph
e
+ 1)
and
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