參數(shù)資料
型號(hào)： MAX3273
廠(chǎng)商： Maxim Integrated Products, Inc.
英文描述： 32-Bit Digital Signal Controller with Flash 100-LQFP -40 to 125
中文描述： +3.3V、2.5Gbps低功耗激光驅(qū)動(dòng)器
文件頁(yè)數(shù)： 10/15頁(yè)
文件大?。?/td> 984K
代理商： MAX3273
M
+3.3V, 2.5Gbps Low-Power Laser Driver
10
______________________________________________________________________________________
Programming the Bias Current
with APC Disabled
When using the MAX3273 in open-loop operation, the
bias current is determined by the R
BIASMAX
resistor. To
select this resistor, see the I
BIASMAX
vs. R
BIASMAX
graph
in the
Typical Operating Characteristics
and select the
value of R
BIASMAX
that corresponds to the required
I
BIASMAX
at +25
°
C. Ground the APCFILT1 pin for open-
loop operation.
Programming the Bias Current
with APC Enabled
When the MAX3273
’
s APC feature is used, program the
average optical power by adjusting the APCSET resis-
tor. To select this resistor, determine the desired moni-
tor current to be maintained over temperature and life.
See the I
MD
vs. R
APCSET
graph in the
Typical
Operating Characteristics
and select the value of R
APC-
SET
that corresponds to the required current.
When using the MAX3273 in closed-loop operation, the
R
BIASMAX
resistor sets the maximum bias current avail-
able to the laser diode over temperature and life. The
APC loop can subtract from this maximum value but
cannot add to it. See the I
BIASMAX
vs. R
BIASMAX
graph
in the
Typical Operating Characteristics
and select the
value of R
BIASMAX
that corresponds to the end-of-life
bias current at +85
°
C.
Interfacing with Laser Diodes
To minimize optical output aberrations caused by sig-
nal reflections at the electrical interface to the laser
diode, a series-damping resistor (R
D
) is required (see
the
Typical Application Circuit
). Additionally, the
MAX3273 outputs are optimized for a 25
load.
Therefore, the series combination of R
D
and R
L
(where
R
L
represents the laser-diode resistance) should equal
25
. Typical values for RD are 18
to 23
. For best
performance, a bypass capacitor (0.01μF typical)
should be placed as close as possible to the anode of
the laser diode. Depending on the exact characteristics
of the laser diode and PC board layout, a resistor (R
P
)
of 50
to 100
in parallel with pullup inductor L
P1
can
be useful in damping overshoot and ringing in the opti-
cal output.
In some applications (depending on laser-diode para-
sitic inductance), an RC-shunt network between the
laser cathode and ground helps minimize optical out-
put aberrations. Starting values for most coaxial lasers
are R = 75
in series with C = 3.3pF. These values
should be experimentally adjusted until the optical out-
put waveform is optimized.
Pattern-Dependent Jitter
When transmitting NRZ data with long strings of con-
secutive identical digits (CIDs), LF droop can occur
and contribute to pattern-dependent jitter (PDJ). To
minimize this PDJ, three external components must be
properly chosen: capacitor (C
APCFILT
), which domi-
nates the APC loop time constant; pullup inductor (L
P
);
and AC-coupling capacitor (C
D
).
To filter out noise effects and guarantee loop stability,
the recommended value for C
APCFILT
is 0.01μF. This
results in an APC loop bandwidth of 100kHz or a time
constant of 15μs. As a result, the PDJ associated with
an APC loop time constant can be ignored.
The time constant associated with the output pullup
inductor (L
P
≈
L
P2
) and the AC-coupling capacitor (C
D
)
affects the PDJ. For such a second-order network, the
PDJ is dominated by L
P
because of the low frequency
cutoff. For a data rate of 2.5Gbps, the recommended
value for C
D
is 0.056μF. During the maximum CID peri-
od, limit the peak voltage droop to less than 12% of the
average (6% of the amplitude). The time constant can
be estimated by:
If
τ
LP
= L
P
/ 25
, and t = 100UI
≈
40ns, then L
P
=
7.8μH. To reduce the physical size of this element (L
P
),
use of SMD ferrite beads is recommended (Figure 2).
To achieve even greater immunity to droop, use an
optional third inductor (33μH, L
P3
in Figure 2).
Input Termination Requirement
The MAX3273 data and clock inputs are CML compati-
ble. However, it is not necessary to drive the IC with a
standard CML signal. As long as the specified differen-
tial voltage swings are met, the MAX3273 operates
properly.
Calculating Power Consumption
The junction temperature of the MAX3273 dice must be
kept below +150
°
C at all times. The total power dissipa-
tion of the MAX3273 can be estimated by the following:
P = V
CC
×
I
CC
+ (V
CC
- V
f
)
I
BIAS
+ I
MOD
(V
CC
- 25
I
MOD
/ 2)
where I
BIAS
is the maximum bias current set by
R
BIASMAX
, I
MOD
is the modulation current, and V
f
is the
typical laser forward voltage.
Junction temperature = P(W)
37 (
°
C/W)
12
τ
1
7 8
.
%
=
=
LP
τ
e
t
t
LP
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MAX3273E/D 功能描述:激光驅(qū)動(dòng)器 RoHS:否 制造商:Micrel 數(shù)據(jù)速率:4.25 Gbps 工作電源電壓:3 V to 3.6 V 電源電流:80 mA 最大工作溫度:+ 85 C 封裝 / 箱體:QFN-16 封裝:Tube
MAX3273EGG 功能描述:激光驅(qū)動(dòng)器 2.5Gbps Low-Power Laser Driver RoHS:否 制造商:Micrel 數(shù)據(jù)速率:4.25 Gbps 工作電源電壓:3 V to 3.6 V 電源電流:80 mA 最大工作溫度:+ 85 C 封裝 / 箱體:QFN-16 封裝:Tube
MAX3273EGG-T 功能描述:激光驅(qū)動(dòng)器 2.5Gbps Low-Power Laser Driver RoHS:否 制造商:Micrel 數(shù)據(jù)速率:4.25 Gbps 工作電源電壓:3 V to 3.6 V 電源電流:80 mA 最大工作溫度:+ 85 C 封裝 / 箱體:QFN-16 封裝:Tube
MAX3273ETG+ 功能描述:激光驅(qū)動(dòng)器 2.5Gbps Low-Power Laser Driver RoHS:否 制造商:Micrel 數(shù)據(jù)速率:4.25 Gbps 工作電源電壓:3 V to 3.6 V 電源電流:80 mA 最大工作溫度:+ 85 C 封裝 / 箱體:QFN-16 封裝:Tube
MAX3273ETG+T 功能描述:激光驅(qū)動(dòng)器 2.5Gbps Low-Power Laser Driver RoHS:否 制造商:Micrel 數(shù)據(jù)速率:4.25 Gbps 工作電源電壓:3 V to 3.6 V 電源電流:80 mA 最大工作溫度:+ 85 C 封裝 / 箱體:QFN-16 封裝:Tube
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