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FEATURES
155Mbps to 3.2Gbps Laser Diode Driver for VCSELs*
60ps Rise and Fall Times, 10ps Deterministic Jitter
Eye Diagram is Stable and Consistent Across
Modulation Range and Temperature
1mA to 12mA Modulation Current
Easy Board Layout, Laser can be Remotely Located
if Desired
No Input Matching or AC Coupling Components
Needed
On-Chip ADC for Monitoring Critical Parameters
Digital Setup and Control with I
Emulation and Set-Up Software Available**
Operates Standalone or with a Microprocessor
On-Chip DACs Eliminate External Potentiometers
Constant Current or Automatic Power Control
First and Second Order Temperature Compensation
On-Chip Temperature Sensor
Extensive Eye Safety Features
Single 3.3V Supply
4mm × 4mm QFN Package
U
APPLICATIO S
Gigabit Ethernet and Fibre Channel Transceivers
SFF and SFP Transceiver Modules
Proprietary Fiber Optic Links
TYPICAL APPLICATIO
3.3V
24LC00 EEPROM
IN SOT-23 PACKAGE
V
DD
SDA
SCL
CONTROLLER
EN
FAULT
+
IN
100Ω
SERIALIZER
–
IN
V
SS
Figure 1. VCSEL Transmitter with Automatic Power Control
2
TM
C
Serial Interface
MD
ADC
DIGITAL
DAC
SRC
DAC
MODA
+
MODB
–
3.2Gbps
MODULATOR
WARNING: POTENTIAL EYE HAZARD.
SEE "EYE SAFETY INFORMATION"
3.3V, 3.2Gbps VCSEL Driver
DESCRIPTIO
®
The LTC
5100 is a 3.2Gbps VCSEL driver offering an
unprecedented level of integration and high speed perfor-
mance. The part incorporates a full range of features to
ensure consistently outstanding eye diagrams. The data
inputs are AC coupled, eliminating the need for external
capacitors. The LTC5100 has a precisely controlled 50Ω
output that is DC coupled to the laser, allowing arbitrary
placement of the IC. No coupling capacitors, ferrite beads
or external transistors are needed, simplifying layout,
reducing board area and the risk of signal corruption. The
unique output stage of the LTC5100 confines the modula-
tion current to the ground system, isolating the high speed
signal from the power supply to minimize RFI.
The LTC5100 supports fully automated production with its
extensive monitoring and control features. Integrated 10-bit
DACs eliminate the need for external potentiometers. An on-
board 10-bit ADC provides the laser current and voltage,
as well as monitor diode current and temperature. Status
information is available from the I
back and statistical process control.
An internal digital controller compensates laser tempera-
ture drift and provides extensive laser safety features.
, LTC and LT are registered trademarks of Linear Technology Corporation.
2
I
C is a trademark of Philips Electronics N.V.
*Vertical Cavity Surface Emitting Laser
**Downloadable from www.linear.com
10nF
50Ω
1mA/DIV
ARBITRARY
DISTANCE
5100 F01
LTC5100
2
C serial interface for feed-
3.2Gbps Electrical Eye Diagram
50ps/DIV
5100 TA01
sn5100 5100fs
1
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Related Manuals for Linear Technology LTC5100
Summary of Contents for Linear Technology LTC5100
- Page 1 Gigabit Ethernet and Fibre Channel Transceivers SFF and SFP Transceiver Modules , LTC and LT are registered trademarks of Linear Technology Corporation. Proprietary Fiber Optic Links C is a trademark of Philips Electronics N.V.
- Page 2 LTC5100 ABSOLUTE AXI U RATI GS PACKAGE/ORDER I FOR ATIO (Note 1) ............. 4V ORDER PART DD(HS) TOP VIEW – , IN (Cml_en = 1) (Note 6) NUMBER Peak Voltage ... V – 1.2V to V + 0.3V DD(HS) DD(HS)
-
Page 3: Electrical Characteristics
LTC5100 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25°C; V = 3.3V, I = 24mA; I = 12mA (I = 24mA); 49.9Ω, 1% DD(HS) resistor from SRC (Pin 14) to MODA (Pin 11); 50Ω, 1% load AC coupled to MODB (Pin 10); 10nF, 10% capacitor from SRC (Pin 14) to ;... - Page 4 LTC5100 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25°C; V = 3.3V, I = 24mA; I = 12mA (I = 24mA); 49.9Ω, 1% DD(HS) resistor from SRC (Pin 14) to MODA (Pin 11); 50Ω, 1% load AC coupled to MODB (Pin 10); 10nF, 10% capacitor from SRC (Pin 14) to ;...
- Page 5 LTC5100 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25°C; V = 3.3V, I = 24mA; I = 12mA (I = 24mA); 49.9Ω, 1% DD(HS) resistor from SRC (Pin 14) to MODA (Pin 11); 50Ω, 1% load AC coupled to MODB (Pin 10); 10nF, 10% capacitor from SRC (Pin 14) to ;...
- Page 6 LTC5100 ELECTRICAL CHARACTERISTICS denotes the specifications which apply over the full operating temperature range, otherwise specifications are at T = 25°C. V = 3.3V, I = 24mA; I = 12mA (I = 24mA); 49.9Ω, 1% DD(HS) resistor from SRC (Pin 14) to MODA (Pin 11); 50Ω, 1% load AC coupled to MODB (Pin 10); 10nF, 10% capacitor from SRC (Pin 14) to ;...
- Page 7 50% crossings of the modulation signal when compared to the ideal time crossings. The specification for the Note 19: The LTC5100 ADC digitizes the logarithm of the monitor diode LTC5100 pertains to the electrical modulation signal. The K28.5 pattern is current.
- Page 8 LTC5100 TYPICAL PERFOR A CE CHARACTERISTICS = 3.3V, T = 25°C, Cml_en = 0, Lpc_en = 1, transmitter enabled, unless otherwise noted. Test circuit shown in Figure 5. DD(HS) Optical Eye Diagram at 3.2Gbps Optical Eye Diagram at 2.5Gbps Effect of Peaking Control on the...
- Page 9 LTC5100 TYPICAL PERFOR A CE CHARACTERISTICS = 3.3V, T = 25°C, Cml_en = 0, Lpc_en = 1, transmitter enabled, unless otherwise noted. Test circuit shown in Figure 5. DD(HS) Rise and Fall Times vs I at the Rise and Fall Times...
- Page 10 LTC5100 TYPICAL PERFOR A CE CHARACTERISTICS = 3.3V, T = 25°C, Cml_en = 0, Lpc_en = 1, transmitter enabled, unless otherwise noted. DD(HS) Hot Plug with EN Active in Hot Plug with EN Active in Start-Up with Slow Ramping CCC Mode...
- Page 11 LTC5100 PI FU CTIO S (Pins 1, 4, 9, 12, 17): Ground for Digital, Analog and MODA, MODB (Pins 11, 10): High Speed Laser Modula- High Speed Circuitry. These pins are internally connected. tion Outputs. MODA and MODB are connected on-chip Connect Pins 1, 4, 9 and 12 to the ground plane with and driven by an open-drain output transistor.
-
Page 12: Block Diagra
LTC5100 BLOCK DIAGRA FAULT PIN Over_current DRIVER Over_pwr Transmit_en TRANSMIT AND Under_pwr Fault Under_voltage UNDERVOLTAGE FAULT FAULT DETECTION CONTROLLER En_polarity Mem_load_errorr Flt_drv_mode Flt_pin_polarity LOGARITHMIC AMPLIFIER 100µA 100µA DATA BUS CURRENT MD(MON) ATTENUATOR SERIAL DIGITAL – Over_pwr INTERFACE POWER LIMIT COMPARATORS... - Page 13 LTC5100 FU CTIO AL DIAGRA S Imd rng Md polarity FAULT CURRENT Imd adc LOG AMP SCL 7 ATTENUATOR Is rng USER_ADC. Data Apc gain – – Imd set Imd error ∑ Imd nom Is dac TEMP MINIMUM Imd tc1...
- Page 14 LTC5100 FU CTIO AL DIAGRA S FAULT SCL 7 Is rng (BIAS CURRENT) Is rng Is adc – – Im rng – Ib_set Ib_error ∑ Ib nom Is dac TEMP Ib gain Ib tc1 TEMP SENSOR COMP Ib tc2 T int adc –...
-
Page 15: Test Circuit
LTC5100 TEST CIRCUIT 1.8V POWER SOURCE 10nF 10nF 50Ω = 50Ω MODA FROM LTC5100 = 50Ω = 50Ω BERT – MODB SCOPE MICROWAVE BLOCKING CAPACITOR FAULT SCL V DD(HS) 10nF 5100 F05 RESISTORS: 0402 SURFACE MOUNT CAPACITORS: 0402 SURFACE MOUNT, X7R DIELECTRIC Figure 5. - Page 16 VCSELs in high speed fiber optic transceivers. The chip and monitor diode response characteristics. incorporates several features that make it very compact The high speed inputs of the LTC5100 are internally and easy-to-use while delivering exceptional high speed terminated in 50Ω and internally AC coupled, eliminating performance.
- Page 17 Figure 12 through Figure 16 define terminology that is Modulator Architecture used throughout this data sheet. The current delivered by The LTC5100 drives common cathode lasers using a . The average modulation current the SRC pin is called I method called “shunt switching”. As shown in Figure 12,...
- Page 18 (11) TERM MODA = Is • R The LTC5100 can digitize the voltage across the termina- The average voltage on the laser diode relative to ground tion resistor using the on-chip ADC, which can give a more is V (see Figure 12 and Figure 15). The voltage on the...
- Page 19 When using the internal temperature sensor (Ext_temp_en Configuration register. This bit is denoted by: = 0), the temperature measurements are taken by the on- chip ADC, and ∆T is the change in the LTC5100 die tem- SYS_CONFIG.Apc_en perature relative to a user defined nominal temperature: In many cases this bit field will simply be referred to as ∆T = T_int_adc –...
- Page 20 Is_rng = 2 quality of the eye diagrams in spite of laser impedance variations. The reflection coefficient is sufficiently low that the LTC5100 can drive the laser over an arbitrary length of Is_rng = 1 RECOMMENDED transmission line, as shown in Figure 19. A well designed...
- Page 21 LTC5100 OPERATIO Figure 19 shows how the LTC5100 achieves a low reflec- dynamic impedance or if a narrow, high impedance PC tion coefficient. The unavoidable capacitance of the high board trace is needed to connect to the laser. speed driver transistor, bond pads and ESD protection...
- Page 22 This provision maximizes the compliance IN APC AND CCC MODES voltage range of the modulation output. The LTC5100 controls the modulation current with a The difference equation for the modulation servo loop is: digital servo control loop using feedback from the on-chip ADC.
- Page 23 The range should be selected so that the monitor diode current stays within the guaranteed Figure 3 is a functional diagram of the LTC5100 operating current limits over temperature. in automatic power control (APC) mode. In APC mode, the...
- Page 24 20:1 variation in settling time. Imd_rng = 1 The LTC5100 uses two techniques to fully compensate for variations in the laser and monitor diode characteristics, Imd_rng = 0 achieving constant settling times under all conditions.
- Page 25 The set point value for the monitor diode current, Imd_set in Figure 3, can be changed with temperature to compen- Figure 4 is a functional diagram of the LTC5100 operating sate the temperature dependence of the monitor diode in constant current control (CCC) mode. In CCC mode, the response.
- Page 26 LTC5100 OPERATIO current can be temperature compensated with first and with each servo iteration. In this case the step response of second order temperature coefficients. the loop is given by, assuming Im_nom = 0 : Servo Control Ib adc ...
- Page 27 Ext_temp_en. AND EYE SAFETY The temperature compensated expression for Ib_set is The LTC5100 is compatible with the Gigabit Interface given by: Converter (GBIC) specification, but includes additional features and safety interlocks. Figure 27 shows the state ...
- Page 28 OPERATIO The EN pin and the Soft_en bit must both be active to The LTC5100 has sophisticated eye safety and fault han- enable the transmitter, providing an extra degree of safety dling features. Five types of faults are detected: low supply...
- Page 29 FAULT pin. Overview The state of the LTC5100 can be monitored by reading the The ADC in the LTC5100 is a 10-bit, dual slope integrating FLT_STATUS register. See Table 21 for a description of the converter with excellent linearity and noise rejection.
- Page 30 USER_ADC BIAS AND MODULATION CURRENT User Access to the ADC Setting Lpc_en to zero turns off the LTC5100’s digital Laser Power Controller (see Figure 2). The source and The results of each conversion cycle in Table 2 are stored modulation DACs (Is_dac and Im_dac) can then be written in user accessible registers.
- Page 31 0x0A 5100 F28 Figure 28. I C Serial Read/Write Sequences (LTC5100 Responses are Shown in Bold Italics) to Use It, V1.0” by Philips Semiconductor. The 7-bit I MSB .. LSB. The register set and I C command set for the bus address for the LTC5100 is 0x0A (hex).
- Page 32 The LTC5100 generates I C address 0xAE (1010_1110 nal EEPROM. If an EEPROM responds, the LTC5100 reads binary) when accessing the EEPROM, making it compat- 16-bytes of data and transfers this data to the internal ible with a wide range of EEPROM sizes.
- Page 33 LTC5100 by setting the Operating_mode The LTC5100 attempts to read the EEPROM every 64ms bit. When this bit is set, the LTC5100 stops searching for until it successfully loads its registers or until the an external EEPROM and takes commands from the mi- Operating_mode bit is set.
- Page 34 LTC5100 REGISTER DEFI ITIO S Table 7. Register Set Overview REGISTER NAME CONSTANT CURRENT AUTOMATIC POWER C COMMAND READ/WRITE REFERENCE REGISTER GROUP CONTROL MODE CONTROL MODE CODE (HEX) ACCESS INFORMATION System Operating SYS_CONFIG “ 0x10 Table 8 Configuration LOOP_GAIN “...
- Page 35 .Operating_mode Digital Operating Control Mode Select Whether the LTC5100 Operates Autonomously or Under External Control. 0: Standalone Operation: Configuration Parameters are Loaded from an External EEPROM at Power Up. 1: Externally Controlled Operation: Configuration Parameters are Set by an External Microprocessor or Test Computer.
- Page 36 LTC5100 REGISTER DEFI ITIO S Table 9. Register: LOOP_GAIN—Control Loop Gain (I C Command Code 0x1E) REGISTER RESET VALUE .BITFIELD (BIN) FUNCTION AND VALUES .Reserved 15:8 .Ib_gain Bias Current or APC Loop Gain (.Apc_gain in APC This Bit Field Modifies the Open-Loop Gain of the Bias Current Servo Control Loop. The Effect of This Mode) Bit Field Differs in Constant Current Control (CCC) Mode and in Automatic Power Control (APC) Mode.
- Page 37 LTC5100 REGISTER DEFI ITIO S Table 12. Register: IB (IMD)—Laser Bias Current Register (Monitor Diode Current in APC Mode) (I C Command Code 0x15) REGISTER RESET VALUE .BITFIELD (BIN) FUNCTION AND VALUES .Reserved 15:12 .Is_rng Source Current Range Is_rng Sets the Full-Scale Range of the SRC Pin Current. The Table Below Shows the Available Ranges.
- Page 38 LTC5100 REGISTER DEFI ITIO S Table 14. Register: IB_TC2 (IMD_TC2)—Laser Bias/Monitor Diode Current Second Order Temperature Coefficient C Command Code 0x17) REGISTER RESET VALUE .BITFIELD (BIN) FUNCTION AND VALUES .Reserved 15:8 .Ib_tc2 (.Imd_tc2 Second Order Temperature Coefficient for Bias Current or Monitor Diode Current in APC Mode) This Bit Field is a Signed 8-Bit, Two’s Complement Integer.
- Page 39 LTC5100 REGISTER DEFI ITIO S Table 16. Register: IM_TC1—Laser Modulation Current First Order Temperature Coefficient (I C Command Code 0x1A) REGISTER RESET VALUE .BITFIELD (BIN) FUNCTION AND VALUES .Reserved 15:8 .Im_tc1 First Order Temperature Coefficient for Modulation Current This Bit Field is a Signed 8-Bit, Two’s Complement Integer. Thus its Value Ranges from –128 to 127.
- Page 40 Nominal Temperature T_nom is the Temperature with Respect to Which All Temperature Compensation Calculations are Made. T_nom is Usually the Temperature at Which the LTC5100 and Laser Diode were Set Up In Production. The Scaling is 512K or 239°C Full Scale, Corresponding to 0.5°C/LSB T_nom = (T + 273°C)/0.5°C, Where T is the Nominal Temperature in Degrees Celsius.
- Page 41 Auto_shutdn_en Automatic Transmitter Shutdown Enable 0: Disabled: When a Fault Occurs the LTC5100 Continues to Drive the Laser. This Mode Allows a Microprocessor or Test Computer to Mediate the Decision to Shut Down the Transmitter. The Microprocessor can Turn Off the Transmitter by Driving the EN Pin Inactive or by Clearing the Soft_en Bit in the SYS_CONFIG Register.
- Page 42 1: A First Fault Has Been Detected. .Faulted Faulted 0: The LTC5100 is Not in the Faulted State. 1: A Fault Has Occurred and the LTC5100 Has Entered the Faulted State (the Transmitter is Not Disabled Unless Auto_shutdn_en is Set). .Under_votlage Undervoltage Fault Indicator (Always Enabled) Cleared-on-read Indicates That a Power Supply Undervoltage Event Occurred.
- Page 43 LTC5100 REGISTER DEFI ITIO S Table 22. Register: IB_LIMIT—Laser Bias Current Limit (I C Command Code 0x11) REGISTER RESET VALUE .BITFIELD (BIN) FUNCTION AND VALUES .Reserved 15:7 .Ib_limit Laser Bias Current Limit This Bit Field is an Unsigned 7-Bit Integer Sets the Detection Level for an Over_current Fault.
- Page 44 .T_int_adc ADC Reading of the Internal (Die) Temperature (10-Bit Unsigned Integer) This Bit Field Contains the Result of the Last Conversion of the LTC5100’s Internal Die Temperature. The Scaling is 512°K or 239°C Full Scale, Corresponding to 0.5°C/LSB. T = T_int_adc • 0.5°C – 273°C, Where T is the Internal Temperature in Degrees Celsius.
- Page 45 LTC5100 REGISTER DEFI ITIO S Table 26. Register: IM_ADC—Modulation Current ADC (I C Command Code 0x06) REGISTER RESET VALUE .BITFIELD (BIN) FUNCTION AND VALUES .Reserved 15:10 .Im_adc ADC Reading of the Modulation Current (10-Bit Unsigned Integer) Im_adc Contains the Last ADC Conversion of the Average Modulation Current Delivered at the MODA and MODB Pins.
- Page 46 LTC5100 REGISTER DEFI ITIO S Table 29. Register: IM_DAC—Modulation Current DAC (I C Command Code 0x02) REGISTER RESET VALUE .BITFIELD (BIN) FUNCTION AND VALUES .Reserved 15:10 .Im_dac DAC Setting for the Peak-to-Peak Modulation Current (the Combined MODA and MODB Pin Currents) Read Access to This DAC is Always Available.
- Page 47 LTC5100 APPLICATIO S I FOR ATIO HIGH SPEED DESIGN AND LAYOUT and 12) have webs of copper connecting them to the cen- tral pad to reduce ground inductance. The laser modula- Figure 29 and Figure 30 show the schematic and layout of...
- Page 48 The termination resistor, R1, and its decoupling capacitor, LTC5100. However, placement of the EEPROM is not C1, are placed as close as possible to the LTC5100 to critical. It can be placed several centimeters from the reduce inductance. Inductance in these two components LTC5100 or on the back of the PC board if desired.
- Page 49 LTC5100 provides temperature compen- ing power supply filtering. It consists of the LTC5100 with sation for the monitor diode current and the laser modu- EEPROM for storing setup parameters, L1 and C3 for lation current.
- Page 50 MD. H2 is a 2mm, 2-pin header with 0.5mm laser on at power up. square pins. The LTC5100’s FAULT output is available at the test turret The demo board includes an EEPROM that provides non- labeled “FAULT.” The FAULT pin can be software config- volatile storage for the LTC5100’s configuration settings...
- Page 51 Information furnished by Linear Technology Corporation is believed to be accurate and reliable. However, no responsibility is assumed for its use. Linear Technology Corporation makes no represen- tation that the interconnection of its circuits as described herein will not infringe on existing patent rights.
-
Page 52: Related Parts
Design Note 273 “Fiber Optic Communication Systems Benefit from Tiny, Low Noise Avalanche Photodiode Bias Supply” sn5100 5100fs Linear Technology Corporation LT/TP 0903 1K • PRINTED IN USA 1630 McCarthy Blvd., Milpitas, CA 95035-7417 (408) 432-1900 FAX: (408) 434-0507 www.linear.com © LINEAR TECHNOLOGY CORPORATION 2003...
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