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Semtech |
GN25L95
2.5 Gbps CMOS Burst Mode Laser Driver & Limiting Post
Amplifier with On-Chip Digital Diagnostic Monitoring
Main Features
• 100 mA bias current and 90 mA
modulation current output drive capability
• On-chip Digital Diagnostic Monitoring
(DDMI)
• Automatic Mean Power and Automatic
Extinction Ratio control
• Fast burst-mode loop settling time
• Current DAC output for APD bias control
• TX_SD and rogue ONU alarm function
• True average Tx burst power monitor
• Tx fault detection and safety logic
• Power down and sleep mode support
• CSFP I2C addressing support
Applications
• EPON & GPON FTTh ONU/ONT
• BOSA-on-Board ONU
• SFF/SFP & CSFP modules
General Description
The GN25L95 is a combined burst mode
laser driver and limiting post amplifier
designed for fiber optic transceiver modules.
The GN25L95 features on-chip digital
diagnostic monitoring and digital set-up. This
enables a complete solution for SFP/SFF
optical transceiver modules.
A fully compliant SFF-8472 digital
diagnostic monitoring solution can be
realised by connecting an external 8k
EEPROM.
The GN25L95 features automatic mean
power and automatic extinction ratio control
functions for robust and reliable control of
laser operating conditions over temperature.
Auto-ranging A/D converters with digitized
monitoring, an internal temperature sensor
and an on-chip DAC for controlling an
external APD bias circuit are also included.
Consuming 90 mA from a 3.3 V supply the
GN25L95 is packaged in a 4x4 mm QFN 28
pin RoHS package rated from -40 to +95 °C.
Block Diagram
Package
VCC_TX VCC_RX VCC_DIG LOS/SD
RXOUT+
RXOUT-
BEN+
BEN-
CML
BURST
ENABLE
Limiter
LOS
&
Filter
RXIN+
Gain
RXIN-
APD
DAC
APD_DAC
TXIN+
TXIN-
RX_SLEEP
SDA
SCL
EE_SDA
EE_SCL
DATA
INPUT
STATE MACHINE
DDMI
CONTROLLER
NVM
DIGITAL
INTERFACE
EEPROM
CONTROLLER
MOD
DRIVER
APC & AUTO ER CONTROL
BIAS
DRIVER
Burst
Mean
Power
Monitor
SAFETY LOGIC &
CONTROL
TX
SD
DIGITAL
ADC &
TEMP
SENSOR
LASER+
LASER-
BIAS+
BIAS-
TX_SD
MPD
RSSI_IN
ADC_IN
GND TX_DISABLE/ TX_FAULT
TX_SLEEP
28 27 26 25 24 23 22
SD/LOS 1
21 TX_SD
RXOUT- 2
20 TX_FAULT
RXOUT+ 3
VCC_DIG 4
GN25L95
19 LASER+
18 LASER-
SDA 5
17 VCC_TX
SCL 6
16 BIAS+
EE_SDA 7
15 BIAS-
8 9 10 11 12 13 14
Figure 1 – GN25L95 Functional Block diagram
GN25L95
Advanced Datasheet
Rev 1.0 – 28 January 2013
www.semtech.com
Figure 2 – GN25L95 Package
1
Proprietary & Confidential
Table of Contents
Main Features ......................................................................................................................................... 1
Applications ............................................................................................................................................. 1
General Description ................................................................................................................................ 1
Block Diagram ......................................................................................................................................... 1
Package .................................................................................................................................................. 1
Table of Contents .................................................................................................................................... 2
Table of Figures ...................................................................................................................................... 4
Package Diagram & Pin Descriptions ..................................................................................................... 6
Typical Operating Characteristics ......................................................................................................... 15
Functional Block Diagram ..................................................................................................................... 16
Functional Description........................................................................................................................... 17
Power Supplies and Start-up Sequence ........................................................................................... 17
GN25L95 State Machine Controller .................................................................................................. 18
Modes of Operation ........................................................................................................................... 19
Internal NVM mode ........................................................................................................................ 19
External EEPROM mode ............................................................................................................... 20
External MCU mode....................................................................................................................... 21
Start-up Sequence ......................................................................................................................... 22
Transmitter Features ......................................................................................................................... 24
Transmitter Input Stage ................................................................................................................. 24
Modulation Stage ........................................................................................................................... 27
MOD_DAC ..................................................................................................................................... 28
Modulation LUT.............................................................................................................................. 29
Automatic Extinction Ratio Control ................................................................................................ 30
MOD_MAX ..................................................................................................................................... 31
Active Back Termination ................................................................................................................ 32
Bias Stage...................................................................................................................................... 33
APCSET_DAC ............................................................................................................................... 33
APCSET LUT................................................................................................................................. 34
BIAS_DAC ..................................................................................................................................... 35
Bias LUT ........................................................................................................................................ 36
Burst Control Stage........................................................................................................................ 37
APC_CLOCK_SET ........................................................................................................................ 38
DIG_AVG_SET .............................................................................................................................. 38
APC Fast Start-up Algorithm ......................................................................................................... 40
COUNT_INC .................................................................................................................................. 41
BIAS_MAX ..................................................................................................................................... 41
MD_MAX........................................................................................................................................ 43
Transmitted Signal Detect Status Output ...................................................................................... 44
Rogue ONU Monitoring.................................................................................................................. 45
GPON Power Levelling .................................................................................................................. 48
Tx Crossing Point Adjust................................................................................................................ 48
Eye Safety Stage ........................................................................................................................... 50
The APC loop and Auto ER loop are protected by a single-point of failure check such that any
opens or shorts to these control loops causes a TX_FAULT condition as required by IEC-60825.
The GN25L95 circuit response to single point failures is shown in ............................................... 50
Alarms and Warnings..................................................................................................................... 50
TX_FAULT Output ......................................................................................................................... 50
Circuit Responses to Single Points Of Failure............................................................................... 53
Safety Logic Timing ....................................................................................................................... 55
TX_DISABLE on Rx LOS .............................................................................................................. 59
Receiver Features ............................................................................................................................. 60
Receiver Input Stage ..................................................................................................................... 60
Receiver CML Output Stage.......................................................................................................... 60
Receiver Digital Control Functions Block Diagram........................................................................ 61
Receiver Data Output Polarity Invert Function .............................................................................. 61
Receiver Data Output Amplitude Control....................................................................................... 61
Receiver Data Output Slew Control............................................................................................... 62
GN25L95
Advanced Datasheet
Rev 1.0 – 28 January 2013
2
Proprietary & Confidential
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