參數(shù)資料
型號(hào)： MAX3656E
廠商： Maxim Integrated Products, Inc.
英文描述： Dual LVDS Transmitter/Receiver 16-SOIC -40 to 85
中文描述： 155Mbps至2.5Gbps突發(fā)模式激光驅(qū)動(dòng)器
文件頁(yè)數(shù)： 8/16頁(yè)
文件大?。?/td> 734K
代理商： MAX3656E
M
Detailed Description
The MAX3656 laser driver has three main parts: a high-
speed modulator, a high-speed bias driver, and a laser-
biasing block with automatic power control (see the
Functional Diagram
). Both the bias and modulation output
stages are composed of differential pairs with program-
mable current sources. The circuit design is optimized for
high-speed, low-voltage (3.3V), DC-coupled operation.
The device is ideal for burst-mode operation with turn-on
and turn-off times less than 2ns. The MAX3656 can be
configured for nonburst-mode applications (continuous
mode) by connecting BEN high.
The MAX3656 modulation output is optimized for dri-
ving a 15
load. The modulation current can swing up
to 85mA for data rates less than or equal to 1.25Gbps
and up to 60mA for data rates greater than 1.25Gbps
when the laser is DC-coupled. To interface with the
laser diode, a damping resistor (R
D
) is required for
impedance matching. The combined resistance due to
the series damping resistor and the equivalent series
resistance (ESR) of the laser diode should be equal to
15
. The OUT- pin should be connected with a 15
resistor to V
CC
. To reduce optical output aberrations
and duty-cycle distortion caused by laser diode para-
sitic inductance, an RC shunt network is necessary.
The currents in the BIAS output switch at high speeds
when bursting. Therefore, the BIAS+ pin should be con-
nected directly through a resistor to the cathode of the
laser. The BIAS- pin should be connected to V
CC
through a 15
resistor.
Automatic Power Control
To maintain constant average optical power, the
MAX3656 incorporates a digital automatic power-con-
trol (APC) loop to compensate for the changes in laser
threshold current over temperature and lifetime. A
back-facet photodiode mounted in the laser package
converts the optical power into a photocurrent. The
APC loop adjusts the laser bias current so the monitor
current is matched to a reference current set by R
APCSET
.
At startup, the APC loop traverses through a pseudo-
binary search algorithm to set the proper monitor current
that translates to the proper bias current. When BEN is
high, the APC loop maintains constant optical power by
digitally controlling the bias current. When BEN is low,
the APC loop digitally stores the bias current value of the
previous burst. The APC loop is reset in two ways, either
power cycling or toggling the
EN
pin.
An external resistor (R
BIASMAX
) sets the maximum allow-
able bias current during closed-loop operation and sets
the bias current during open-loop operation. An APC fail-
ure flag (
FAIL
) is set low during initialization and when
the bias current cannot be adjusted to achieve the
desired average optical power.
APC closed-loop operation requires that the user set
three currents with external resistors connected between
GND, BIASMAX, MODSET, and APCSET pins. Detailed
guidelines for these resistor settings are described in the
Design Procedure
section.
If necessary, the MAX3656 is fully operational without
APC. To operate the MAX3656 open loop, connect a
50k
resistor from APCSET to ground and leave the
MD pin unconnected. In this case, two external resis-
tors connected from BIASMAX and MODSET to GND
directly set the laser current.
APC Failure Monitor
The MAX3656 provides an APC failure monitor (TTL) to
indicate an APC loop-tracking failure.
FAIL
is set low
when the APC loop cannot adjust the bias current to
maintain the desired monitor current. For example, the
laser diode requires more bias current (to maintain a
constant optical output) than maximum bias current set
by R
BIASMAX
. The bias current is limited and
FAIL
is
asserted. In an alternate example, assume that a circuit
failure causes the cathode of the laser diode to be short-
ed to GND, thereby causing an uncontrolled high optical
output. In this case, the APC loop cannot decrease the
user current, and
FAIL
is asserted.
FAIL
is also set low
during initialization.
Slow-Start
For safety reasons, at initial power-up or after toggling
EN
, the MAX3656 incorporates a slow-start circuit that
provides a typical delay of 450ns during the beginning
of APC loop initialization.
Enable Control
The MAX3656 features a chip-enable function. When
EN
is high, the bias and modulation currents are off and
the digital state of the APC loop is reset. When
EN
is
toggled from a high to a low, the APC loop begins ini-
tialization. The initialization time is typically 2.1μs
(LONGB = low) and 3.72μs (LONGB = high).
APC Loop Initialization
The digital APC loop is reset whenever the power is
turned off and/or the
EN
input is driven high. When
power is turned on or when
EN
is toggled low, the APC
loop automatically performs an initialization routine that
quickly adjusts the bias current from its reset level to its
initialized level. The initialized bias current level is
defined to be within 3.8mA of the final bias current level
set by the APCSET resistor. Once initialized, the APC
155Mbps to 2.5Gbps Burst-Mode
Laser Driver
8
_______________________________________________________________________________________
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相關(guān)代理商/技術(shù)參數(shù)
參數(shù)描述
MAX3656E/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
MAX3656ETA 制造商:Maxim Integrated Products 功能描述:- Rail/Tube
MAX3656ETG 功能描述:激光驅(qū)動(dòng)器 .155-2.5Gbps Burst Mode 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
MAX3656ETG+ 功能描述:激光驅(qū)動(dòng)器 .155-2.5Gbps Burst Mode 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
MAX3656ETG+ 制造商:Maxim Integrated Products 功能描述:IC LASER DIODE DRIVER 2.5GBPS TQFN-24
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