Datasheet

155Mbps to 2.5Gbps Burst-Mode Laser Driver
Maxim Integrated 11
MAX3643
< 2.56mV
BURST-ENABLE (BEN±) IN
≤ 125μs FOR BPON/GPON
INTERNAL MDIN VOLTAGE SAMPLER
BENOUT OUTPUT
100μs
3μs
1.2V
MDOUT
Figure 2. Sample-and-Hold Timing Diagram
Enable Input
An LVCMOS input, EN, is provided to disable both bias
and modulation currents under external control. The
maximum time to disable laser current with the EN con-
trol is 375ns.
Setting the Current Limit
A current limiter is provided to protect the laser diode
by shutting down both bias and modulation currents
when total current exceeds a value set by the resistor
connected from IMAX to ground. Do not use less than
3kΩ R
I
MAX
. See the I
BIAS
+ I
MOD
Current Threshold vs.
R
IMAX
graph in the Typical Operating Characteristics.
Programming the MODSET and
BIASSET Inputs
To program the laser modulation current using a cur-
rent DAC, connect VMSET to VREF, attach the DAC to
the MODSET pin and set the current according to:
I
MOD
= I
MODSET
x 88
To program the laser modulation current using a resis-
tor or digital potentiometer, connect VMSET to VREF,
attach a resistor from the MODSET pin to ground, and
set the current according to:
To program the laser modulation current using a PWM
voltage DAC (requiring a high-impedance load), attach
a DAC output to the VMSET pin, connect a resistor from
the MODSET pin to ground as shown in the Typical
Applications Circuit , and set the current according to:
I
V
RR
MOD
DAC
MODSET MOD
=
+
× 88
I
V
RR
MOD
MODSET MOD
=
+
×
12
88
.