ltc5100 Linear Technology Corporation, ltc5100 Datasheet - Page 48

• Manufacturer Part Number: ltc5100
• Description: 3.3v, 3.2gbps Vcsel Driver
• Manufacturer: Linear Technology Corporation

APPLICATIO S I FOR ATIO
LTC5100
The termination resistor, R1, and its decoupling capacitor,
C1, are placed as close as possible to the LTC5100 to
reduce inductance. Inductance in these two components
causes high frequency peaking and overshoot in the
current delivered to the laser. R1 and C1 are folded against
each other so that their mutual inductance and counter-
flowing current partially cancel their self-inductance. C1
has two vias to the ground plane and a trace directly to Pin
12. The layout shows the EEPROM placed next to the
48
SDA
V
SCL
SS
Figure 32. Layout of the Minimum Reflection Coeffieicnt Circuit Using 0402 Passive Components
V
+TX_DATA
–TX_DATA
DD
ENABLE
U
EEPROM
+ 3.3V
FAULT
V
SS
U
Figure 31. Schematic of a Minimum Output Reflection Coefficient Circuit
V
NC
CC
Z
O
= 50
L1
FERRITE
BEAD
W
SOT23 PACKAGE
1
2
3
4
EEPROM
IN
NC
V
IN
24LC00
CC
V
V
U
+
–
V
IN
IN
V
SS
SS
SS
SS
SDA
SCL
V
+
–
SS
FAULT
4
1
2
3
V
16
5
DD
16
5
PROGRAMMING
SDA
EN
15
LTC5100
6
15
6
PADS
SRC
SCL V
LTC5100. However, placement of the EEPROM is not
critical. It can be placed several centimeters from the
LTC5100 or on the back of the PC board if desired.
The transmission line connecting the MODB pin to the
laser has a short length of minimum width trace. The net
inductance of this section of trace helps compensate on-
chip capacitance to further reduce reflections from the
chip.
14
14
7
7
DD(HS)
MD
13
8
13
MODA
MODB
8
12
11
10
C3
10nF
9
V
V
SS
SS
V
V
SS
SS
MODA
MODB
12
11
10
9
50
FIBER
R1
Z
O
= 50
10nF
10nF
R1
C2
C1
C1
L1
C3
5100 F32
5100 F29
C2
sn5100 5100fs