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參數(shù)資料
| 型號： | MAX3967D |
| 廠商： | Maxim Integrated Products, Inc. |
| 元件分類： | LED驅動器 |
| 英文描述： | 270Mbps SFP LED Driver |
| 中文描述： | 270Mbps的SFP LED驅動器 |
| 文件頁數(shù)： | 8/14頁 |
| 文件大?。?/td> | 319K |
| 代理商： | MAX3967D |
M
nal compensation. The compensation network can be
optimized by adding additional components between
V
CCOUT
and OUT+.
The MAX3967 includes a complementary output driver,
which is switched 180° out of phase with the main out-
put. This configuration helps to maintain constant cur-
rent flow from the voltage supply, reducing noise and
EMI. A large diode and a 5
resistor are connected in
series with the negative output (OUT-) to emulate the
LED load at OUT+.
Peaking Current
The prebias resistor provides peaking current to improve
the LED switching speed. The peaking magnitude is
given by the following equation:
The peaking amplitude is equal for rising and falling
data transitions.
Design Proc edure
S elec t an LED
For best performance, select a high-efficiency, low-
inductance LED. LED inductance causes large voltage
swings and ringing.
Program the Modulation-Current T empc o
Select a modulation-current tempco that provides near-
ly constant LED output power as temperature varies.
For the minimum tempco, connect TCMIN to the TC pin.
For a tempco of approximately 3600ppm/°C, connect
TC to TCNOM and leave TCMIN unconnected. For the
maximum tempco, leave TCMIN, TCNOM, and TC
unconnected.
See the Modulation-Current Tempco vs. R
TC
graph in
the
Typical Operating Characteristics
to program a cus-
tom tempco. From the graph, determine the appropriate
resistor and connect it between TCMIN and TC.
For example, if an LED requires a 5000ppm/°C tempco,
choose R
TC
of 8.3k
.
Program the Modulation Current
Determine the required modulation current at T
A
= +25°C.
Then select the appropriate value of R
MODSET
from the
Modulation Current vs. R
MODSET
graph in the
Typical
Operating Characteristics
.
For example, to program 75mA modulation current, the
graph indicates an R
MODSET
value of 750
for maxi-
mum tempco (12,000ppm/°C) and 1k
for nominal
tempco (3600ppm/°C). By interpolation, choose an
R
MODSET
of 792
for a tempco of 5000ppm/°C.
Program Prebias V oltage
Determine the LED prebias voltage that produces an
acceptable trade-off between peaking current and extinc-
tion ratio. See Table 1 for PB1, PB2, and PB3 settings.
Layout Considerations
For optimum performance, total load inductance should
not exceed 10nH. Load inductance includes LED
inductance, LED package lead inductance, and circuit-
board traces. Keep the connections between the
MAX3967 OUT pins and the LED as short as possible
to minimize inductance.
Chip-and-wire (hybrid) technology reduces package
inductance significantly, and provides the best possible
performance.
Use good high-frequency layout techniques and a
multilayer board with an uninterrupted ground plane.
Power supplies should be capacitively bypassed to the
ground plane with surface-mount capacitors located
near the power-supply pins.
I
PEAK
LED
V
PREBIAS
-V
78
=
270Mbps S FP LED Driver
8
_______________________________________________________________________________________
Table 1. LED Prebias Voltage
PB1
PB2
PB3
PREBIAS (V)
Open
V
EE
Open
V
EE
Open
V
EE
Open
V
EE
Open
Open
V
EE
V
EE
Open
Open
V
EE
V
EE
Open
Open
Open
Open
V
EE
V
EE
V
EE
V
EE
0.400
0.475
0.550
0.625
0.700
0.775
0.850
0.925
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