MAX3646 Maxim Integrated Products, MAX3646 Datasheet - Page 13

• Manufacturer Part Number: MAX3646
• Description: 155Mbps to 622Mbps Sff/sfp Laser Driver
• Manufacturer: Maxim Integrated Products

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Maxim’s Laser Drivers to Laser Diodes for more informa-
tion on AC-coupling laser drivers to laser diodes.
For compliance:
The APC loop filter capacitor (C
to balance the requirements for fast turn-on and mini-
mal interaction with low frequencies in the data pattern.
The low-frequency cutoff is:
High-frequency noise can be filtered with an additional
cap, C
The MAX3646 is designed so turn-on time is faster than
1ms for most laser gain values (η x ρ
smaller value of C
V
C
MD
OUT+
APC
CDR
, from the MD pin to ground:
(µF) ≅ 68 / (f
= V
Laser Driver with Extinction Ratio Control
REPRESENTS A CONTROLLED-IMPEDANCE TRANSMISSION LINE.
CC
______________________________________________________________________________________
APC
- I
C
MD
MOD
3dB
reduces turn-on time. Careful
≅ C
/ 2 x (R
(kHz) x (η x
R
R
APC
MODBCOMP
R
MODTCOMP
0.1µF
0.1µF
TH_TEMP
APC
/ 4
D
Determine C
+ R
) must be selected
IN+
IN-
MODBCOMP
MODTCOMP
TH_TEMP
MON
L
ρ MON
) ≥ 0.75V
). Choosing a
155Mbps to 622Mbps SFF/SFP
)
1.1
APC
MAX3646
C
balance between turn-on time and low-frequency cutoff
may be needed at low data rates for some values of
laser gain.
Figures 6 and 7 show simplified input and output cir-
cuits for the MAX3646 laser driver. If dice are used,
replace package parasitic elements with bondwire par-
asitic elements.
To minimize loss and crosstalk, keep the connections
between the MAX3646 output and the laser diode as
short as possible. Use good high-frequency layout
techniques and multilayer boards with uninterrupted
ground plane to minimize EMI and crosstalk. Circuit
boards should be made using low-loss dielectrics. Use
controlled-impedance lines for data inputs, as well as
the module output.
+3.3V
APC
Typical Application Circuit
OPTIONAL SHUTDOWN
OUT+
OUT-
BIAS
MD
CIRCUITRY
15Ω
FERRITE BEAD
10Ω
Layout Considerations
+3.3V
+3.3V
Interface Models
C
MD
0.01µF
13