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PDF MAX3738 Data sheet ( Hoja de datos )
| Número de pieza | MAX3738 | |
| Descripción | 155Mbps to 4.25Gbps SFF/SFP Laser Driver with Extinction Ratio Control | |
| Fabricantes | Maxim Integrated Products | |
| Logotipo |  |
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19-3162; Rev 2; 12/08
EVAALVUAAILTAIOBNLEKIT
www.DataSheet4U.com
155Mbps to 4.25Gbps SFF/SFP Laser Driver
with Extinction Ratio Control
General Description
The MAX3738 is a +3.3V laser driver designed for mul-
tirate transceiver modules with data rates from
155Mbps to 4.25Gbps. Lasers can be DC-coupled to
the MAX3738 for reduced component count and ease
of multirate operation.
Laser extinction ratio control (ERC) combines the features
of automatic power control (APC), modulation compensa-
tion, and built-in thermal compensation. The APC loop
maintains constant average optical power. Modulation
compensation increases the modulation current in pro-
portion to the bias current. These control loops, com-
bined with thermal compensation, maintain a constant
optical extinction ratio over temperature and lifetime.
The MAX3738 accepts differential data input signals.
The wide 5mA to 60mA (up to 85mA AC-coupled) mod-
ulation current range and up to 100mA bias current
range, make the MAX3738 ideal for driving FP/DFB
lasers in fiber optic modules. External resistors set the
required laser current levels. The MAX3738 provides
transmit disable control (TX_DISABLE), single-point
fault tolerance, bias-current monitoring, and photocur-
rent monitoring. The device also offers a latched failure
output (TX_FAULT) to indicate faults, such as when the
APC loop is no longer able to maintain the average
optical power at the required level. The MAX3738 is
compliant with the SFF-8472 transmitter diagnostic and
SFP MSA timing requirements.
The MAX3738 is offered in a 4mm x 4mm, 24-pin thin
QFN package and operates over the extended -40°C to
+85°C temperature range.
Applications
Multirate OC-3 to OC-48 FEC Transceivers
Gigabit Ethernet SFF/SFP and GBIC
Transceivers
1Gbps/2Gbps/4Gbps Fibre Channel SFF/SFP
and GBIC Transceivers
Features
♦ Single +3.3V Power Supply
♦ 47mA Power-Supply Current
♦ 85mA Modulation Current
♦ 100mA Bias Current
♦ Automatic Power Control (APC)
♦ Modulation Compensation
♦ On-Chip Temperature Compensation
♦ Self-Biased Inputs for AC-Coupling
♦ Ground-Referenced Current Monitors
♦ Laser Shutdown and Alarm Outputs
♦ Enable Control and Laser Safety Feature
Ordering Information
PART
TEMP RANGE
PIN-PACKAGE
MAX3738ETG
-40°C to 85°C
24 Thin QFN-EP*
MAX3738ETG+
-40°C to 85°C
24 Thin QFN-EP*
+Denotes a lead(Pb)-free/RoHS-compliant package.
*EP = Exposed pad.
Pin Configuration
TOP VIEW
24 23 22 21 20 19
MODTCOMP 1
18 MD
VCC 2
17 VCC
IN+ 3
IN- 4
MAX3738
16 OUT+
15 OUT-
VCC 5
TX_DISABLE 6
*EP
78
14 VCC
13 BIAS
9 10 11 12
Typical Application Circuit appears at end of data sheet.
*THE EXPOSED PADDLE MUST BE SOLDERED TO SUPPLY
GROUND ON THE CIRCUIT BOARD.
PIN1 INDICATED BY + ON LEAD-FREE PACKAGE.
________________________________________________________________ Maxim Integrated Products 1
For pricing, delivery, and ordering information, please contact Maxim Direct at 1-888-629-4642,
or visit Maxim’s website at www.maxim-ic.com.
1 page  
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155Mbps to 4.25Gbps SFF/SFP Laser Driver
with Extinction Ratio Control
Typical Operating Characteristics (continued)
(VCC = +3.3V, CAPC = 0.01µF, IBIAS = 20mA, IMOD = 30mA, TA = +25°C, unless otherwise noted.)
PHOTODIODE CURRENT vs. RAPCSET
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0.1
1 10
RAPCSET (kΩ)
100
2.0
1.8
1.6
1.4
1.2
1.0
0.8
0.6
0.4
0.2
0
0
RANDOM JITTER
vs. MODULATION CURRENT
10 20 30 40 50 60 70 80
IMOD (mA)
90
TEMPERATURE COMPENSATION vs.
RTH_TEMP (RMODTCOMP = 500Ω)
100
90 RTH_TEMP = 12kΩ
80
RTH_TEMP = 7kΩ
70
RTH_TEMP = 4kΩ
60
RTH_TEMP = 2kΩ
50
40
30
-10 0 10 20 30 40 50 60 70 80 90
TEMPERATURE (°C)
DETERMINISTIC JITTER
vs. MODULATION CURRENT
50
45 2.7Gbps
40
35
30
25
20
15
10
5
0
0 10 20 30 40 50 60 70 80 90
IMOD (mA)
COMPENSATION (K) vs. RMODBCOMP
10
1
0.1
0.01
0.001
0.01 0.1
1
RMODBCOMP (kΩ)
10
100
TEMPERATURE COMPENSATION vs.
RTH_TEMP (RMODTCOMP = 10kΩ)
44
42 RTH_TEMP = 12kΩ
40 RTH_TEMP = 7kΩ
38 RTH_TEMP = 4kΩ
36 RTH_TEMP = 2kΩ
34
32
30
-10 0 10 20 30 40 50 60 70 80 90 100
TEMPERATURE (°C)
_______________________________________________________________________________________ 5
5 Page 
www.DataSheet4U.com
155Mbps to 4.25Gbps SFF/SFP Laser Driver
with Extinction Ratio Control
Table 2. Circuit Responses to Various Single-Point Faults
PIN
CIRCUIT RESPONSE TO OVERVOLTATGE OR
SHORT TO VCC
TX_FAULT Does not affect laser power.
TX_DISABLE Modulation and bias currents are disabled.
The optical average power increases, and a fault occurs
IN+ if VPC_MON exceeds the threshold. The APC loop
responds by decreasing the bias current.
The optical average power decreases and the APC loop
IN- responds by increasing the bias current. A fault state
occurs if VBC_MON exceeds the threshold voltage.
MD This disables bias current. A fault state occurs.
CIRCUIT RESPONSE TO UNDERVOLTAGE OR
SHORT TO GROUND
Does not affect laser power.
Normal condition for circuit operation.
The optical average power decreases, and the APC loop
responds by increasing the bias current. A fault state
occurs if VBC_MON exceeds the threshold voltage.
The optical average power increases and a fault occurs
if VPC_MON exceeds the threshold. The APC loop
responds by decreasing the bias current.
The APC circuit responds by increasing the bias current
until a fault is detected; then a fault* state occurs.
SHUTDOWN
Does not affect laser power. If the shutdown circuitry is
used, the laser current is disabled.
Does not affect laser power.
BIAS
In this condition, the laser forward voltage is 0V and no
light is emitted.
Fault state* occurs. If the shutdown circuitry is used, the
laser current is disabled.
OUT+
The APC circuit responds by increasing the bias current Fault state* occurs. If the shutdown circuitry is used, the
until a fault is detected; then a fault state* occurs.
laser current is disabled.
OUT-
PC_MON
BC_MON
Does not affect laser power.
Fault state* occurs.
Fault state* occurs.
Does not affect laser power.
Does not affect laser power.
Does not affect laser power.
APCFILT1 IBIAS increases until VBC_MON exceeds the threshold
voltage.
IBIAS increases until VBC_MON exceeds the threshold
voltage.
APCFILT2
IBIAS increases until VBC_MON exceeds the threshold
voltage.
IBIAS increases until VBC_MON exceeds the threshold
voltage.
MODSET Does not affect laser power.
Fault state* occurs.
APCSET Does not affect laser power.
Fault state* occurs.
*A fault state asserts the TX_FAULT pin, disables the modulation and bias currents, and asserts the SHUTDOWN pin.
Safety Circuitry
The safety circuitry contains a disable input
(TX_DISABLE), a latched fault output (TX_FAULT), and
fault detectors (Figure 5). This circuitry monitors the
operation of the laser driver and forces a shutdown if a
fault is detected (Table 1). The TX_FAULT pin should
be pulled high with a 4.7kΩ to 10kΩ resistor to VCC as
required by the SFP MSA. A single-point fault can be a
short to VCC or GND. See Table 2 to view the circuit
response to various single-point failure. The transmit
fault condition is latched until reset by a toggle or
TX_DISABLE or VCC. The laser driver offers redundant
laser diode shutdown through the optional shutdown
circuitry as shown in the Typical Application Circuit.
This shutdown transistor prevents a single-point fault at
the laser from creating an unsafe condition.
Safety Circuitry Current Monitors
The MAX3738 features monitors (BC_MON, PC_MON)
for bias current (IBIAS) and photocurrent (IMD). The
monitors are realized by mirroring a fraction of the cur-
rents and developing voltages across external resistors
connected to ground. Voltages greater than VREF at
PC_MON or BC_MON result in a fault state. For exam-
ple, connecting a 100Ω resistor to ground at each mon-
itor output gives the following relationships:
VBC_MON = (IBIAS / 82) x 100Ω
VPC_MON = IMD x 100Ω
External sense resistors can be used for high-accuracy
measurement of bias and photodiode currents. On-chip
isolation resistors are included to reduce the number of
components needed to implement this function.
______________________________________________________________________________________ 11
11 Page | ||
| Páginas | Total 16 Páginas | |
| PDF Descargar | [ Datasheet MAX3738.PDF ] | |
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