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參數(shù)資料
| 型號： | MAX3261ECJ |
| 廠商： | MAXIM INTEGRATED PRODUCTS INC |
| 元件分類： | 其它接口 |
| 英文描述： | Single +5V, Fully Integrated, 1.25Gbps Laser Diode Driver |
| 中文描述： | SPECIALTY INTERFACE CIRCUIT, PQFP32 |
| 封裝： | TQFP-32 |
| 文件頁數(shù)： | 8/12頁 |
| 文件大?。?/td> | 230K |
| 代理商： | MAX3261ECJ |
Table 1. MAX3261 Truth Table
M
S ingle +5V, Fully Integrated,
1.25Gbps Laser Diode Driver
8
_______________________________________________________________________________________
the IPIN node will drop below 2.6V. This will trigger the
failout comparator, which provides a TTL signal indicat-
ing laser failure. The FAILOUT output asserts only if the
monitor-diode current is low, not in the reverse situation
where the monitor current exceeds IPINSET. FAILOUT is
an open-collector output that requires an external pull-up
resistor of 2.7k
to V
CC
.
The transconductance amplifier can source or sink cur-
rents up to approximately 1mA. Since the laser bias
generator has a gain of approximately 40, the APC
function has a limit of approximately 40mA (up or
down) from the initial set point. To take full advantage
of this adjustment range, it may be prudent to program
the laser bias current slightly higher than required for
normal operation. However, do not exceed the I
BIASOUT
absolute maximum rating of 75mA.
To maintain APC loop stability, a 1000pF bypass capaci-
tor may be required across the photodiode. If the APC
function is not used, leave IBIASFB unconnected.
Enable Inputs
The MAX3261 provides complementary enable inputs
(ENB+, ENB-) for interfacing with open-fiber-control
architecture. The laser is disabled by reducing the ref-
erence voltage outputs (VREF1, VREF2). Only one logic
state will enable laser operation (Table 1).
With a 1000pF stability capacitor, the MAX3261 modula-
tion and bias can be enabled and disabled within 5μs
(Figure 3). This timing satisfies the requirements of the
Open Fiber Control system used in Fibre Channel
networks.
T emperature Considerations
The MAX3261 output currents are programmed by cur-
rent mirrors. These mirrors each have a 2V
BE
temperature
coefficient. The reference voltage (VREF) is adjusted
2V
BE
so these changes largely cancel, resulting in output
currents that are very stable with respect to temperature
(see Typical Operating Characteristics).
Wire Bonding Die
For reliable operation, the MAX3261 has gold metalliza-
tion. Make connections to the die with gold wire only,
using ball bonding techniques. Wedge bonding is not
recommended. Pad size is 4mils.
__________________Design Proc edure
Interfac ing S uggestions
Use high-frequency design techniques for the board
layout of the MAX3261 laser driver. High-speed inter-
faces often require fixed-impedance transmission lines
(Figure 5). Adding some damping resistance in series
with the laser raises the load impedance, making the
transmission line more realizable, and it also helps
reduce power consumption (see the section Reducing
Power Consumption. Minimize any series inductance
to the laser, and place a bypass capacitor as close to
the laser’s anode as possible.
Power connections labeled V
CC
A are used to supply the
laser modulation and laser bias circuits. V
CC
B connec-
tions supply the bias-generator and automatic-power
control circuits. For optimum operation, isolate these sup-
plies from each other by independent bypass filtering.
V
CC
A, V
CC
B, GNDA, and GNDB all have multiple pins.
Connect all pins to optimize the MAX3261
’
s high-
frequency performance. Ground connections between
signal lines (VIN+, VIN-, OUT+, OUT-) improve the quali-
ty of the signal path by reducing the impedance of the
interconnect. Multiple connections, in general, reduce
inductance in the signal path and improve the high-
speed signal quality. GND pins should be tied to the
ground plane with short runs and multiple vias. Avoid
ground loops, since they are a source of high-frequency
interference.
The MAX3261 data inputs accept PECL input signals,
which require 50
termination to (V
CC
- 2V). Figure 4
shows alternative termination techniques. When a ter-
mination voltage is not available, use the Thevenin-
equivalent termination. When interfacing with a
non-PECL signal source, use one of the other alterna-
tive termination methods shown in Figure 4.
Bias Network Compensation
When driving the laser diode with transmission lines, it is
important to maintain a constant load impedance in
order to minimize aberrations due to reflections. The
inductive nature of laser packages will cause the laser
impedance to increase with frequency, and the parasitic
capacitance of the laser driver bias output (IBIASOUT)
has some loading effects at high frequency. Of these
two effects, the loading due to the laser lead induc-
tance dominates. Impedance variation must be com-
pensated for high-frequency operation. One possible
approach is to use a shunt R-C network in parallel with
the laser diode to compensate for the laser impedance
(Figures 5 and 6). Add an R-L circuit in series with the
bias output to compensate for the IBIASOUT capaci-
tance (Figures 5 and 7).
ENB-
0
0
1
1
1
0
1
0
ENABLED
DISABLED
DISABLED
ENB+
OUTPUT CURRENTS
DISABLED
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