MAX3736 Maxim Integrated Products, MAX3736 Datasheet - Page 8

• Manufacturer Part Number: MAX3736
• Description: SFP Laser Driver
• Manufacturer: Maxim Integrated Products

The output stage is composed of a high-speed differ-
ential pair and a programmable modulation current
source. The MAX3736 is optimized for driving a 15Ω
load; the minimum instantaneous voltage required at
OUT+ is 0.6V. Modulation current swings up to 60mA
are possible.
To interface with the laser diode, a damping resistor
(R
bined resistance of the series damping resistor and the
equivalent series resistance of the laser diode should
equal 15Ω. To reduce optical output aberrations and
duty-cycle distortion caused by laser diode parasitic
inductance, an RC shunt network might be necessary.
Refer to Maxim Application Note HFAN 02.0:
Interfacing Maxim’s Laser Drivers to Laser Diodes for
more information.
At high data rates, e.g., 2.5Gbps, any capacitive load at
the cathode of a laser diode degrades optical output per-
formance. Because the BIAS output is directly connected
to the laser cathode, minimize the parasitic capacitance
associated with the pin by using an inductor to isolate the
BIAS pin parasitics from the laser cathode.
In the absence of input data, the modulation current
switches to OUT-, squelching the transceiver output.
The DIS pin disables the modulation and bias current.
The typical enable time is 2µs for bias current and 1µs
for modulation current. The typical disable time is 200ns
for bias current and 250µs for modulation current. The
DIS pin has a 7.4kΩ internal pullup resistor.
There are three methods for setting the modulation cur-
rent on the MAX3736 laser driver. The current can be
set by using a current DAC, a voltage DAC in series with
a resistor, or by using a resistor connected to GND.
To program the laser modulation current using a cur-
rent DAC, attach the DAC to the MODSET pin and set
the current using the following equation:
3.2Gbps, Low-Power, Compact,
SFP Laser Driver
8
D
) is required for impedance matching. The com-
_______________________________________________________________________________________
Programming the Modulation Current
I
MOD
High-Speed Modulation Driver
=
I
MODSET
Design Procedure
× 85
Disable
To program the laser modulation current using a volt-
age DAC, attach the DAC to the MODSET pin through a
series resistor, R
following equation:
To program the laser modulation current using a resis-
tor, place the resistor from MODSET to ground. I
current can be calculated by the following equation:
There are three methods for setting the bias current on
the MAX3736 laser driver. The current can be set by
using a current DAC, a voltage DAC in series with a
resistor, or by using a resistor connected to GND.
To program the laser bias current using a current DAC,
attach the DAC to the BIASSET pin and set the current
using the following equation:
To program the laser bias current using a voltage DAC,
attach the DAC to the BIASSET pin through a series
resistor, R
ing equation:
To program the laser bias current using a resistor,
place the resistor from BIASSET to ground. I
rent can be calculated by the following equation:
SERIES
I
I
MOD
BIAS
I
MOD
I
BIAS
I
BIAS
Programming the Bias Current
, and set the current using the follow-
SERIES
=
=
=
1 2
1 2
=
=
.
.
R
R
R
R
I
MODSET
V V
V V
BIASET
SERIES
SERIES
BIASET
, and set the current using the
1 2
1 2
−
−
.
.
V
V
DAC
DAC
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×
×
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×
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BIAS
MOD
cur-