MAX3869EHJ+ ,+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APCELECTRICAL CHARACTERISTICS(V = +3.14V to +5.5V, T = -40°C to +85°C. Typical values are at V = +3.3V ..
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MAX7414EUA+ ,5th-Order, Lowpass, Switched-Capacitor Filtersapplications. They feature a+5V (MAX7409/MAX7410)shutdown mode, which reduces the supply current to ..
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MAX7415CPA ,5th-Order / Lowpass / Elliptic / Switched-Capacitor Filtersapplications. They +5V (MAX7408/MAX7411)can be put into a low-power mode, reducing supply+3V (MAX74 ..
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MAX3869EHJ+
+3.3V, 2.5Gbps SDH/SONET Laser Driver with Current Monitors and APC
General DescriptionThe MAX3869 is a complete, single +3.3V laser driver
for SDH/SONET applications up to 2.5Gbps. The
device accepts differential PECL data and clock inputs
and provides bias and modulation currents for driving a
laser. A synchronizing input latch can be used (if a
clock signal is available) to reduce jitter.
An automatic power control (APC) feedback loop is
incorporated to maintain a constant average optical
power over temperature and lifetime. The wide modula-
tion current range of 5mA to 60mA and bias current of
1mA to 100mA are easy to program, making this prod-
uct ideal for use in various SDH/SONET applications.
The MAX3869 also provides enable control, two current
monitors that are directly proportional to the laser bias and
modulation currents, and a failure-monitor output to indi-
cate when the APC loop is unable to maintain the average
optical power. The MAX3869 is available in 32-pin TQFP
and small 32-pin QFN packages as well as dice.
ApplicationsSONET/SDH Transmission Systems
Add/Drop Multiplexers
Digital Cross-Connects
Section Regenerators
2.5Gbps Optical Transmitters
FeaturesSingle +3.3V or +5V Power Supply64mA Supply Current at +3.3VProgrammable Bias Current from 1mA to 100mAProgrammable Modulation Current from
5mA to 60mABias Current and Modulation Current Monitors87ps Rise/Fall TimeAutomatic Average Power Control with Failure
MonitorComplies with ANSI, ITU, and Bellcore
SDH/SONET SpecificationsEnable Control
Ordering Information
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
Typical Application Circuit
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APCELECTRICAL CHARACTERISTICS(VCC= +3.14V to +5.5V, TA= -40°C to +85°C. Typical values are at VCC= +3.3V, IMOD= 30mA, IBIAS= 60mA, TA= +25°C, unless
otherwise noted.) (Note 1)
Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.
Supply Voltage, VCC.............................................-0.5V to +7.0V
Current into BIAS ...........................................-20mA to +150mA
Current into OUT+, OUT-................................-20mA to +100mA
Current into MD.....................................................-5mA to +5mA
Voltage at DATA+, DATA-, CLK+, CLK-, ENABLE,
LATCH, FAIL, BIASMON, MODMON.....-0.5V to (VCC+ 0.5V)
Voltage at APCFILT, CAPC, MODSET,
BIASMAX, APCSET...........................................-0.5V to +3.0V
Voltage at OUT+, OUT-.............................+1.5V to (VCC+ 1.5V)
Voltage at BIAS.........................................+1.0V to (VCC+ 0.5V)
Continuous Power Dissipation (TA= +85°C)
32-Pin TQFP-EP (derate 22.2mW/°C above +85°C)..1444mW
32-Pin QFN (derate 20.84mW/°C above +85°C).......1667mW
Storage Temperature Range.............................-65°C to +165°C
Operating Junction Temperature Range...........-55°C to +150°C
Processing Temperature (die).........................................+400°C
Lead Temperature (soldering, 10s).................................+300°C
ABSOLUTE MAXIMUM RATINGS
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APCELECTRICAL CHARACTERISTICS(VCC= +3.14V to +5.5V, load as shown in Figure 2, TA= -40°C to +85°C. Typical values are at VCC= +3.3V, IMOD= 30mA, TA= +25°C.)
(Note 7)
Note 1:Dice are tested at TA= +25°C only.
Note 2:Tested at RMODSET= 2.49kΩ, RBIASMAX= 1.69kΩ, excluding IBIASand IMOD.
Note 3:Voltage on BIAS pin is (VCC- 1.6V).
Note 4:Both the bias and modulation currents will be switched off if any of the current set pins are grounded.
Note 5:Accuracy refers to part-to-part variation.
Note 6:Assuming that the laser to monitor-diode transfer function does not change with temperature. Guaranteed by design and
characterization.
Note 7:AC characteristics are guaranteed by design and characterization.
Note 8:Measured with 622Mbps 0-1 pattern, LATCH = high.
Note 9:PWD = (wider pulse - narrower pulse) / 2.
Note 10:See Typical Operating Characteristicsfor worst-case distribution.
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
Typical Operating Characteristics (VCC = +3.3V, load as shown in Figure 2, TA= +25°C, unless otherwise noted.)
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APCSUPPLY CURRENT vs. TEMPERATURE
(EXCLUDE IBIAS, IMOD, 25Ω LOAD)
MAX3869-10
TEMPERATURE (°C)
SUPPLY CURRENT (mA)
BIAS-CURRENT MONITOR GAIN
vs. TEMPERATURE
MAX3869-11
TEMPERATURE (°C)
GAIN (I
BIAS
BIASMON
ELECTRICAL EYE DIAGRAM
(IMOD = 30mA, 213-1 +80 CID, 32 TQFP-EP)MAX3869-04
100ps/div
250mV/div
ELECTRICAL EYE DIAGRAM
(IMOD = 60mA, 213-1 +80 CID, 32 TQFP-EP)MAX3869-05
400mV/div
RANDOM JITTER vs. IMOD
MAX3869-06
RANDOM JITTER (psp-p)
Typical Operating Characteristics (continued)(VCC = +3.3V, load as shown in Figure 2, TA= +25°C, unless otherwise noted.)
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
Pin Description
Typical Operating Characteristics (continued)(VCC = +3.3V, load as shown in Figure 2, TA= +25°C, unless otherwise noted.)
_______________Detailed DescriptionThe MAX3869 laser driver consists of two main parts: a
high-speed modulation driver and a laser-biasing block
with automatic power control (APC). The circuit design
is optimized for both high-speed and low-voltage
(+3.3V) operation. To minimize the pattern-dependent
jitter of the input signal at speeds as high as 2.5Gbps,
the device accepts a differential PECL clock signal for
data retiming. When LATCH is high, the input data is
synchronized by the clock signal. When LATCH is low,
the input data is directly applied to the output stage.
The output stage is composed of a high-speed differential
pair and a programmable modulation current source.
Since the modulation output drives a maximum current
of 60mA into the laser with an edge speed of 100ps,
large transient voltage spikes can be generated (due to
the parasitic inductance). These transients and the
laser forward voltage leave insufficient headroom for
the proper operation of the laser driver if the modulation
output is DC-coupled to the laser diode. To solve this
problem, the MAX3869’s modulation output is designed
to be AC-coupled to the cathode of a laser diode. An
external pull-up inductor is necessary to DC-bias the
modulation output at VCC. Such a configuration isolates
laser forward voltage from the output circuitry and
allows the output at OUT+ to swing above and below
the supply voltage VCC. A simplified functional diagram
is shown in Figure 4.
The MAX3869 modulation output is optimized for driv-
ing a 25Ωload; the minimum required voltage at OUT+
is 2.0V. Modulation current swings of 80mA are possi-
ble, but due to minimum power-supply and jitter
requirements at 2.5Gbps, the specified maximum mod-
ulation current is limited to 60mA. To interface with the
laser diode, a damping resistor (RD) is required for
impedance matching. An RC shunt network may also
be necessary to compensate for the laser-diode para-
sitic inductance, thereby improving the optical output
aberrations and duty-cycle distortion.
At the data rate of 2.5Gbps, any capacitive load at the
cathode of a laser diode will degrade the optical output
performance. Since the BIAS output is directly connect-
ed to the laser cathode, minimize the parasitic capaci-
tance associated with this pin by using an inductor to
isolate the BIAS pin from the laser cathode.
Automatic Power Control To maintain constant average optical power, the
MAX3869 incorporates an APC loop to compensate for
the changes in laser threshold current over temperature
and lifetime. A back-facet photodiode mounted in the
MAX3869
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
Pin Description (continued)
MAX3869laser package is used to convert the optical power into
a photocurrent. The APC loop adjusts the laser bias
current so that the monitor current is matched to a ref-
erence current set by RAPCSET. The time constant of
the APC loop is determined by an external capacitor
(CAPC). To eliminate the pattern-dependent jitter asso-
ciated with the APC loop-time constant, and to guaran-
tee loop stability, the recommended value for CAPCis
0.1µF.
When the APC loop is functioning, the maximum allow-
able bias current is set by an external resistor, RBIASMAX.
An APC failure flag (FAIL) is set low when the bias current
can no longer be adjusted to achieve the desired aver-
age optical power. To filter out the APC loop noise, use
an external capacitor at APCFILT with a recommended
value of 0.1µF.
APC closed-loop operation requires the user to set three
currents with external resistors connected between
ground and BIASMAX, MODSET, and APCSET. Detailed
guidelines for these resistor settings are described in
the Design Proceduresection.
Open-Loop OperationIf necessary, the MAX3869 is fully operational without
APC. In this case, the laser current is directly set by two
external resistors connected from ground to BIASMAX
and MODSET. See the Design Proceduresection for
more details on open-loop operation.
+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Current Monitors and APC
