Datasheet

ManualsBrandsANALOG DEVICES ManualsPMICsPMIC - laser controller Laser diode driver LFCSP 24 VQ Surface-mount

3.3 V, 50 Mbps to 4.25 Gbps,

Single-Loop, Laser Diode Driver

ADN2871

Rev. A

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FEATURES

SFP/SFF and SFF-8472 MSA-compliant

SFP reference design available

50 Mbps to 4.25 Gbps operation

Automatic average power control

Typical rise/fall time 60 ps

Supports VCSEL, DFB, and FP lasers

Bias current range 2 mA to 100 mA

Modulation current range 5 mA to 90 mA

Laser fail alarm and automatic laser shutdown (ALS)

Bias and modulation current monitoring

3.3 V operation

4 mm × 4 mm LFCSP

Voltage setpoint control

Resistor setpoint control

Pin-compatible with

ADN2870

APPLICATIONS

1×/2×/4× Fibre Channel SFP/SFF modules

Multirate OC3 to OC48-FEC SFP/SFF modules

LX-4 modules

DWDM/CWDM SFP modules

1GE SFP/SFF transceiver modules

VCSEL, DFB, and FP transmitters

GENERAL DESCRIPTION

The ADN2871 laser diode driver is designed for advanced SFP

and SFF modules, using SFF-8472 digital diagnostics. The

ADN2871 supports operation from 50 Mbps to 4.25 Gbps.

Average power and extinction ratio can be set with a voltage

provided by a microcontroller DAC or by a trimmable resistor

or digital potentiometer. The average power control loop is

implemented using feedback from a monitor photodiode. The

part provides bias and modulation current monitoring as well

as fail alarms and automatic laser shutdown (ALS). The device

interfaces easily with the Analog Devices, Inc. ADuC70xx

family of MicroConverters® and with the ADN289x family of

limiting amplifiers to make a complete SFP/SFF transceiver

solution. An SFP reference design is available. The product is

pin-compatible with the ADN2870 dual-loop LDD, allowing

one PC board layout to work with either device. For dual-loop

applications, refer to the

ADN2870 data sheet.

The product is available in a space-saving 4 mm × 4 mm LFCSP

specified over the −40°C to +85°C temperature range.

Figure 1 shows an application diagram of the voltage setpoint

control with single-ended laser interface.

Figure 36 shows a

differential laser interface.

05228-001

ADI

MICROCONTROLLER

Tx_DISABLE

Tx_FAULT

CONTROL

PAVREF

PAVSET

ADN2871

RPAV

GND

DAC

MPD

ERREF

ERSET

GND

IMOD

DATAP

IMODP

DATAN

IMODN

IBMON IMMON

ALSFAIL

IBIAS

100Ω

CCBIAS

LASER

GND GND

PAVCAP

470Ω1kΩ

GND

1kΩ

ADC

×100

Figure 1. Application Diagram of Voltage Setpoint Control with a Single-Ended Laser Interface

Summary of content (20 pages)

PAGE 1
3.3 V, 50 Mbps to 4.25 Gbps, Single-Loop, Laser Diode Driver ADN2871 FEATURES GENERAL DESCRIPTION SFP/SFF and SFF-8472 MSA-compliant SFP reference design available 50 Mbps to 4.25 Gbps operation Automatic average power control Typical rise/fall time 60 ps Supports VCSEL, DFB, and FP lasers Bias current range 2 mA to 100 mA Modulation current range 5 mA to 90 mA Laser fail alarm and automatic laser shutdown (ALS) Bias and modulation current monitoring 3.
PAGE 2
ADN2871 TABLE OF CONTENTS Features .............................................................................................. 1 Performance Characteristics..................................................... 11 Applications....................................................................................... 1 Theory of Operation ...................................................................... 13 General Description .........................................................................
PAGE 3
ADN2871 SPECIFICATIONS VCC = 3.0 V to 3.6 V. All specifications TMIN to TMAX 1 , unless otherwise noted. Typical values as specified at 25°C. Table 1.
PAGE 4
ADN2871 Parameter ALARM OUTPUT (FAIL) 9 VOFF Min Typ VON IBMON/IMMON DIVISION RATIO IBIAS/IBMON3 IBIAS/IBMON3 IBIAS/IBMON3 IBIAS/IBMON Stability3, 10 IMOD/IMMON IBMON Compliance Voltage SUPPLY ICC 11 VCC (with respect to GND) 12 76 85 92 Unit Conditions/Comments >1.8 V <1.
PAGE 5
ADN2871 SFP TIMING SPECIFICATIONS Table 2. Parameter ALS Assert Time Symbol t_off ALS Negate Time 1 Time to Initialize, Including Reset of FAIL1 FAIL Assert Time ALS to Reset Time Typ 1 Max 5 Unit μs t_on 0.15 0.
PAGE 6
ADN2871 ABSOLUTE MAXIMUM RATINGS Table 3. Parameter VCC to GND IMODN, IMODP All Other Pins Junction Temperature Operating Temperature Range Industrial Storage Temperature Range Junction Temperature (TJ max) LFCSP Power Dissipation 1 θJA Thermal Impedance 2 θJC Thermal Impedance Lead Temperature (Soldering 10 sec) Stresses above those listed under Absolute Maximum Ratings may cause permanent damage to the device.
PAGE 7
ADN2871 ERSET IMMON ERREF VCC IBMON 18 FAIL PIN CONFIGURATION AND FUNCTION DESCRIPTIONS 13 12 19 GND ALS VCC DATAN IMODP DATAP ADN2871 IMODN GND PAVCAP GND NC IBIAS 7 6 NC = NO CONNECT 05228-005 RPAV VCC PAVREF GND PAVSET 1 CCBIAS 24 Figure 6. Pin Configuration—Top View Note: The LFCSP has an exposed paddle that must be connected to ground. Table 4. Pin Function Descriptions Pin No.
PAGE 8
ADN2871 OPTICAL WAVEFORMS VCC = 3.3 V and TA = 25°C, unless otherwise noted. Note: No change to PAVCAP and ERCAP values. MULTIRATE PERFORMANCE USING LOW COST FABRY PEROT TOSA NEC NX7315UA PERFORMANCE OVER TEMPERATURE USING DFB TOSA SUMITOMO SLT2486 (ACQ LIMIT TEST) WAVEFORMS 1000 05228-038 05228-006 (ACQ LIMIT TEST) WAVEFORMS 1001 Figure 7. Optical Eye 2.488 Gbps, 65 ps/DIV, PRBS 231-1 PAV = −4.5 dBm, ER = 9 dB, Mask Margin 25% Figure 10. Optical Eye 2.
PAGE 9
ADN2871 TYPICAL PERFORMANCE CHARACTERISTICS SINGLE-ENDED OUTPUT These performance characteristics were measured using the high speed, electrical single-ended, output circuit shown in Figure 2. 1.2 90 RANDOM JITTER (rms) 1.0 RISE TIME (ps) 60 30 0.8 0.6 0.4 0 20 40 60 MODULATION CURRENT (mA) 80 0 100 05228-014 0 05228-011 0.2 0 20 40 60 80 100 MODULATION CURRENT (mA) Figure 12. Rise Time vs. Modulation Current, IBIAS = 20 mA Figure 14. Random Jitter vs.
PAGE 10
ADN2871 DIFFERENTIAL OUTPUT These performance characteristics were measured using the high speed, electrical differential output circuit shown in Figure 3. 1.2 90 RANDOM JITTER (rms) RISE TIME (ps) 1.0 60 30 0.8 0.6 0.4 0 20 40 60 80 0 100 05228-034 0 05228-032 0.2 0 20 MODULATION CURRENT (mA) 40 60 80 100 MODULATION CURRENT (mA) Figure 18. Random Jitter vs. Modulation Current, IBIAS = 20 mA Figure 16. Rise Time vs.
PAGE 11
ADN2871 PERFORMANCE CHARACTERISTICS 250 60 55 IBIAS = 80mA 190 SUPPLY CURRENT (mA) IBIAS = 40mA 160 130 IBIAS = 20mA IBIAS = 10mA 100 40 0 20 40 60 80 45 40 35 30 25 05228-015 70 50 20 –50 100 05228-016 TOTAL SUPPLY CURRENT (mA) 220 –30 –10 MODULATION CURRENT (mA) 10 30 50 TEMPERATURE (°C) 70 90 110 Figure 23. Supply Current (ICC) vs. Temperature with ALS Asserted, IBIAS = 20 mA Figure 20. Total Supply Current vs.
PAGE 12
ADN2871 TRANSMISSION ON FAIL ASSERTED FAULT FORCED ON PAVSET 05228-022 05228-021 POWER SUPPLY TURN ON Figure 26. FAIL Assert Time,1 μs/DIV Figure 27. Time to Initialize, Including Reset, 40 ms/DIV Rev.
PAGE 13
ADN2871 THEORY OF OPERATION Laser diodes have a current-in to light-out transfer function, as shown in Figure 28. Two key characteristics of this transfer function are the threshold current, Ith, and the slope in the linear region beyond the threshold current, referred to as the slope efficiency, LI. P1 PO P1 + PO PAV = 2 P1 ΔI PO Ith The ADN2871 has two methods for setting the average power (PAV) and extinction ratio (ER).
PAGE 14
ADN2871 VCC VCC VCC Tx_DISABLE VCC L Tx_FAULT VCC FAIL ALS IMODN LASER R MPD IMODP DATAP PAVSET ADI MICROCONTROLLER DAC DATAN 100Ω CONTROL PAVREF VCC ×100 1kΩ CCBIAS IMOD GND ERREF DAC RZ IBIAS RPAV ADC ERSET ADN2871 1kΩ GND IBMON IMMON VCC GND PAVCAP NC GND 470Ω 05228-001 1kΩ GND GND Figure 29.
PAGE 15
ADN2871 RESISTOR SETPOINT CALIBRATION Method 2: Measuring IMPD Across a Sense Resistor In resistor setpoint calibration, Pin PAVREF, Pin ERREF, and Pin RPAV must all be tied to VCC. The average power and extinction ratio can be set using the PAVSET and ERSET pins, respectively. A resistor is placed between the pin and GND to set the current flowing in each pin, as shown in Figure 30. The ADN2871 ensures that both PAVSET and ERSET are kept 1.23 V above GND.
PAGE 16
ADN2871 Resistor Setpoint In resistor setpoint calibration, the current through the resistor from PAVSET to ground is the IMPD current. The recommended method for measuring the IMPD current is to place a small resistor in series with the PAVSET resistor (or potentiometer) and measure the voltage across this resistor, as shown in Figure 34. The IMPD current is then equal to this voltage divided by the value of resistor used. In resistor setpoint calibration, PAVSET is held to 1.
PAGE 17
ADN2871 The 30 Ω transmission line used is a compromise between drive current required and the total power consumed. Other transmission line values can be used, with some modification of the component values. In Figure 35, the R and C snubber values, 24 Ω and 2.2 pF respectively, represent a starting point and must be tuned for the particular model of laser being used. RP, the pull-up resistor, is in series with a very small (0.5 nH) inductor.
PAGE 18
ADN2871 The ADN2871 has a latched, active high monitoring alarm (FAIL). The FAIL alarm output is an open drain in conformance to SFP MSA specification requirements. The ADN2871 has a three-fold alarm system that covers • Use of a bias current higher than expected, probably as a result of laser aging. • Out-of-bounds average voltage at the monitor photodiode (MPD) input, indicating an excessive amount of laser power or a broken loop.
PAGE 19
ADN2871 OUTLINE DIMENSIONS 0.60 MAX 4.00 BSC SQ TOP VIEW 0.50 BSC 3.75 BSC SQ 0.50 0.40 0.30 1.00 0.85 0.80 12° MAX SEATING PLANE 0.80 MAX 0.65 TYP 0.30 0.23 0.18 19 18 24 1 2.25 2.10 SQ 1.95 EXPOSED PAD (BOTTOMVIEW) 13 12 7 PIN 1 INDICATOR 6 0.23 MIN 2.50 REF 0.05 MAX 0.02 NOM 0.20 REF COPLANARITY 0.08 THE EXPOSED PADDLE MUST BE CONNECTED TO GROUND. COMPLIANT TO JEDEC STANDARDS MO-220-VGGD-2 070506-A PIN 1 INDICATOR 0.60 MAX Figure 38.