参数资料
| 型号： | MAX3668EHJ+T |
| 厂商： | Maxim Integrated |
| 文件页数： | 7/12页 |
| 文件大小： | 0K |
| 描述： | IC LSR DRVR 622MBPS 3.63V 32TQFP |
| 产品培训模块： | Lead (SnPb) Finish for COTS Obsolescence Mitigation Program |
| 标准包装： | 2,500 |
| 类型： | 激光二极管驱动器（光纤） |
| 数据速率： | 622Mbps |
| 通道数： | 1 |
| 电源电压： | 3.14 V ~ 5.5 V |
| 电流 - 电源： | 38mA |
| 电流 - 调制： | 75mA |
| 电流 - 偏置： | 80mA |
| 工作温度： | -40°C ~ 85°C |
| 封装/外壳： | 32-TQFP |
| 供应商设备封装： | 32-TQFP（5x5） |
| 包装： | 带卷 (TR) |
| 安装类型： | 表面贴装 |
+3.3V, 622Mbps SDH/SONET
Laser Driver with Automatic Power Control
? ? 2 0 ? + ( R D + r LASER ) ? ?
Automatic Power Control
To maintain constant average optical power, the
MAX3668 incorporates an APC loop to compensate for
the changes in laser threshold current over temperature
and lifetime. A back-facet photodiode mounted in the
laser package is used to convert the optical power into a
photocurrent. The APC loop adjusts the laser bias cur-
rent so the monitor current is matched to a reference cur-
rent set by R APCSET . The time constant of the APC loop
is determined by an external capacitor (C APC ). To elimi-
nate the pattern-dependent jitter associated with the
APC loop-time constant and to guarantee loop stability,
the recommended value for C APC is 0.1μF.
When the APC loop is functioning, the maximum allowable
bias current is set by an external resistor, R BIASMAX . An
APC failure flag ( FAIL ) is set low when the bias current can
no longer be adjusted to achieve the desired average
optical power.
APC closed-loop operation requires the user to set three
currents with external resistors connected between
ground and BIASMAX, MODSET, and APCSET. Detailed
guidelines for these resistor settings are described in
the Design Procedure section.
Open-Loop Operation
If necessary, the MAX3668 is fully operational without
APC. In this case, the laser current is directly set by two
external resistors connected from ground to BIASMAX
and MODSET. Connect a 100k ? resistor from APCSET
to ground and leave MD open for open-loop operation.
Enable Control
The MAX3668 incorporates a laser driver enable func-
tion. When ENABLE is low, both the bias and modulation
currents are off. The typical laser enable time is 250ns.
APC Failure Monitor
The MAX3668 provides an APC failure monitor
(TTL/CMOS) to indicate an APC loop tracking failure. FAIL
is set low when the APC loop can no longer adjust the bias
current to maintain the desired monitor current. This output
is internally pulled up to V CC through a 6k ? resistor.
Table 1. Optical Power Definition
Short-Circuit Protection
The MAX3668 provides short-circuit protection for the
modulation, bias, and monitor current sources. If either
BIASMAX, MODSET, or APCSET is shorted to ground,
the bias and modulation outputs will be turned off.
Design Procedure
When designing a laser transmitter, the optical output is
usually expressed in terms of average power and extinc-
tion ratio. Table 1 gives the relationships that are helpful
in converting between the optical average power and the
modulation current. These relationships are valid if the
average duty cycle of the optical waveform is 50%.
Programming the Modulation Current
In addition to being a function of R MODSET , the modula-
tion current delivered to the laser (I MODL ) also depends
on the values of the series damping resistor (R D ), the
shunt compensation resistance (R FILT ), and the laser
diode’s resistance (see Typical Operating Circuit ).
The modulation current (assuming C FILT <<C D ) into the
laser diode can be represented by the following:
? 2 0 ? ?
I MODL = I MOD ? ?
Assuming R D = 5 ? and r LASER = 5 ? , this equation is
simplified to:
I MODL = I MOD (0.67)
For R D = 5.0 ? and a laser resistance of approximately
5 ? , refer to the Modulation Current vs. Modulation Set
Resistor graph in the Typical Operating Characteristics
and select the value of R MODSET that corresponds to
the required current at +25°C.
Programming the Bias Current
When using the MAX3668 in open-loop operation, the
bias current is determined by the R BIASMAX resistor. To
select this resistor, determine the required bias current
at +25°C. Refer to the Bias Current vs. Maximum Bias
Set Resistor graph in the Typical Operating Character-
istics and select the value of R BIASMAX that corre-
sponds to the required current at +25°C.
PARAMETER
Average Power
Extinction Ratio
Optical Power High
Optical Power Low
Optical Amplitude
Laser Slope Efficiency
Modulation Current
SYMBOL
P AVE
r e
P 1
P 0
Pp-p
η
I MOD
RELATION
P AVE = (P 0 + P 1 ) / 2
r e = P 1 / P 0
P 1 = 2P AVE · r e / (r e + 1)
P 0 = 2P AVE / (r e + 1)
Pp-p = 2P AVE (r e - 1) / (r e + 1)
η = Pp-p / I MOD
I MOD = Pp-p / η
When using the MAX3668 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. Refer to the Bias Current vs. Maximum
Bias Set Resistor 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.
_______________________________________________________________________________________
7
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相关代理商/技术参数 |
参数描述 |
|---|---|
| MAX3668EVKIT | 功能描述:激光驱动器 Evaluation Kit for the MAX3668 RoHS:否 制造商:Micrel 数据速率:4.25 Gbps 工作电源电压:3 V to 3.6 V 电源电流:80 mA 最大工作温度:+ 85 C 封装 / 箱体:QFN-16 封装:Tube |
| MAX3669E/D | 功能描述:激光驱动器 DICE SALES DICE12 RoHS:否 制造商:Micrel 数据速率:4.25 Gbps 工作电源电压:3 V to 3.6 V 电源电流:80 mA 最大工作温度:+ 85 C 封装 / 箱体:QFN-16 封装:Tube |
| MAX3669E/D DIE | 制造商:Maxim Integrated Products 功能描述: |
| MAX3669E/D+ | 功能描述:激光驱动器 RoHS:否 制造商:Micrel 数据速率:4.25 Gbps 工作电源电压:3 V to 3.6 V 电源电流:80 mA 最大工作温度:+ 85 C 封装 / 箱体:QFN-16 封装:Tube |
| MAX3669EHJ | 功能描述:激光驱动器 3.3V 622Mbps SDH/SONET RoHS:否 制造商:Micrel 数据速率:4.25 Gbps 工作电源电压:3 V to 3.6 V 电源电流:80 mA 最大工作温度:+ 85 C 封装 / 箱体:QFN-16 封装:Tube |
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