3.3 V Dual-Loop 50 Mbps to 3.3 Gbps
Laser Diode Driver
ADN2847
Data Sheet
FEATURES
APPLICATIONS
50 Mbps to 3.3 Gbps operation
Single 3.3 V operation
Typical rise/fall time: 80 ps
Bias current range: 2 mA to 100 mA
Modulation current range: 5 mA to 80 mA
Monitor photodiode current: 50 μA to 1200 μA
Dual MPD functionality for DWDM
50 mA supply current at 3.3 V
Closed-loop control of power and extinction ratio
Full current parameter monitoring
Laser fail and laser degrade alarms
Automatic laser shutdown (ALS)
Optional clocked data
Supports FEC rates
48-lead (7 mm × 7 mm) LFCSP package
32-lead (5 mm × 5 mm) LFCSP package
SONET OC-1/3/12/48
SDH STM-0/1/4/16
Fibre Channel
Gigabit Ethernet
DWDM dual MPD wavelength control
GENERAL DESCRIPTION
The ADN2847 uses a unique control algorithm to control both
average power and extinction ratio of the laser diode (LD) after
initial factory setup. External component count and PCB area
are low, as both power and extinction ratio control are fully
integrated. Programmable alarms are provided for laser fail
(end of life) and laser degrade (impending fail).
Optional dual MPD current monitoring is designed into the
ADN2847 specifically for DWDM wavelength control.
The ADN2847 is specified for the −40°C to +85°C temperature
range and is available in a 48-lead LFCSP package and a 32-lead
LFCSP package.
VCC
GND
IMODN
CLKSEL
VCC
VCC
DEGRADE
FAIL
ALS
IMPDMON2
IMPDMON
IBMON
IMMON
FUNCTIONAL BLOCK DIAGRAM
VCC
IMODP
LD
MPD
IMPD
DATAP
DATAN
IMOD
CLKP
IMPD2
CLKN
CONTROL
GND
PSET
IBIAS
VCC
RZ
IBIAS
ASET
GND ERSET
GND
ERCAP
GND
PAVCAP
IDTONE
LBWSET
02745-001
GND
ADN2847
GND
Figure 1.
Rev. B
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Fax: 781.461.3113 ©2003–2012 Analog Devices, Inc. All rights reserved.
ADN2847
Data Sheet
TABLE OF CONTENTS
Features .............................................................................................. 1
Alarms.............................................................................................9
Applications....................................................................................... 1
Monitor Currents ....................................................................... 10
General Description ......................................................................... 1
Dual MPD DWDM Function (48-Lead LFCSP Only) ......... 10
Functional Block Diagram .............................................................. 1
IDTONE (48-Lead LFCSP Only)............................................. 10
Revision History ............................................................................... 2
Data and Clock Inputs............................................................... 10
Specifications..................................................................................... 3
CCBIAS........................................................................................ 10
Timing Diagrams.......................................................................... 4
IBIAS ................................................................................................ 10
Absolute Maximum Ratings............................................................ 5
Automatic Laser Shutdown....................................................... 10
Thermal Resistance ...................................................................... 5
Alarm Interfaces ......................................................................... 11
ESD Caution.................................................................................. 5
Power Consumption .................................................................. 11
Die Pad Coordinates ........................................................................ 6
Laser Diode Interfacing............................................................. 11
Pin Configurations and Function Descriptions ........................... 7
Optical Supervisor...................................................................... 11
Theory of Operation ........................................................................ 9
Outline Dimensions ....................................................................... 14
Control........................................................................................... 9
Ordering Guide .......................................................................... 15
Loop Bandwidth Selection .......................................................... 9
REVISION HISTORY
3/12—Rev. A to Rev. B
Added EPAD Notation .................................................................... 7
Updated Outline Dimensions ....................................................... 14
Changes to Ordering Guide .......................................................... 15
10/06—Rev. 0 to Rev. A
Updated Format..................................................................Universal
Change to Data Sheet Title.............................................................. 1
Changes to Figure 1.......................................................................... 1
Changes to Specifications ................................................................ 3
Added IBIAS Section ......................................................................... 10
Changes to Laser Diode Interfacing Section............................... 11
Changes to Figure 14...................................................................... 12
Changes to Figure 15...................................................................... 13
Changes to Ordering Guide .......................................................... 15
1/03—Revision 0: Initial Version
Rev. B | Page 2 of 16
Data Sheet
ADN2847
SPECIFICATIONS
VCC = 3.0 V to 3.6 V. Temperature range: −40°C to +85°C. All specifications TMIN to TMAX, unless otherwise noted. Typical values specified
at TA = 25°C.
Table 1.
Parameter
LASER BIAS CURRENT (IBIAS, ALS)
Output Current IBIAS
IBIAS when ALS is asserted
ALS Assertion Time
IBIAS Compliance Voltage
CCBIAS Compliance Voltage
MODULATION CURRENT (IMODP, IMODN) 1
Output Current IMOD
Compliance Voltage
IMOD when ALS is Asserted
Rise Time 2
Fall Time2
Random Jitter2
Pulse Width Distortion2
MONITOR PD (MPD, MPD2)
Current
Compliance Voltage
POWER SET INPUT (PSET)
Capacitance
Monitor Photodiode Current into RPSET Resistor
Voltage
EXTINCTION RATIO SET INPUT (ERSET)
Allowable Resistance Range
Voltage
ALARM SET (ASET)
Allowable Resistance Range
Voltage
Hysteresis
CONTROL LOOP
Time Constant
DATA INPUTS (DATAP, DATAN, CLKP, CLKN) 3
V p-p (Single-Ended, Peak-to-Peak)
Input Impedance (Single-Ended)
tSETUP 4
tHOLD4
LOGIC INPUTS (ALS, LBWSET, CLKSEL)
VIH
VIL
ALARM OUTPUTS (FAIL, DEGRADE)
VOH
VOL
IDTONE
Compliance Voltage
IOUT/IIN Ratio
fIN 5
Min
Typ
2
1.2
1.2
5
1.5
80
80
1
15
50
Max
Unit
Conditions/Comments
100
0.1
5
VCC
VCC
mA
mA
μs
V
V
IBIAS < 10% of nominal
80
VCC
0.1
120
120
1.5
mA
V
mA
ps
ps
ps
ps
1200
1.65
μA
V
pF
μA
V
50
1.1
1.2
80
1200
1.3
1.2
1.1
1.2
25
1.3
kΩ
V
25
1.3
kΩ
V
%
1.2
1.1
1.2
5
0.22
2.25
100
sec
sec
500
50
50
100
2.4
mV
Ω
ps
ps
0.8
V
V
0.8
V
V
See Figure 3 for device rise time histogram
See Figure 4 for device fall time histogram
RMS
IMOD = 40 mA
Average current
Average current
Low Loop Bandwidth selection
LBWSET = GND
LBWSET = VCC
Data and clock inputs are ac-coupled
See Figure 2
See Figure 2
Internal 30 kΩ Pull-Up
2.4
User to supply current sink in the range of
50 μA to 4 mA
VCC − 1.5
2
0.01
V
1
Rev. B | Page 3 of 16
MHz
ADN2847
Data Sheet
Parameter
IBMON, IMMON, IMPDMON, IMPDMON2
IBMON, IMMON Division Ratio
IMPDMON, IMPDMON2
IMPDMON to IMPDMON2 Matching
Compliance Voltage
SUPPLY
ICC 6
VCC 7
Min
Typ
Max
Unit
2
VCC −1.2
A/A
A/A
%
V
3.6
mA
V
100
1
0
50
3.3
3.0
Conditions/Comments
IMPD = 1200 μA
IBIAS = IMOD = 0
1
The high speed performance for the die version of ADN2847 can be achieved when using the bonding diagram shown in Figure 6.
Measured into a 25 Ω load using a 11110000 pattern at 2.5 Gbps.
3
When the voltage on DATAP is greater than the voltage on DATAN, the modulation current flows in the IMODP pin.
4
Guaranteed by design and characterization. Not production tested.
5
IDTONE can cause eye distortion.
6
ICCMIN for power calculation in the Power Consumption section is the typical ICC given.
7
All VCC pins should be shorted together.
2
TIMING DIAGRAMS
HOLD
SETUP
tH
tS
02745-002
DATAP/DATAN
CLKP
40
40
30
30
COUNT (%)
20
10
10
78
80
82
84
86 88 90 92
RISE TIME (ps)
94
96
98
100
0
80
02745-007
0
76
20
Figure 3. Rise Time Distribution Under Worst-Case Operating Conditions
82
84
86
88
90 92 94 96
FALL TIME (ps)
98
100 102 104
02745-008
COUNT (%)
Figure 2. Setup and Hold Time
Figure 4. Fall Time Distribution Under Worst-Case Operating Conditions
Rev. B | Page 4 of 16
Data Sheet
ADN2847
ABSOLUTE MAXIMUM RATINGS
THERMAL RESISTANCE
TA = 25°C, unless otherwise noted.
θJA is specified for the worst-case conditions, that is, a device
soldered in a circuit board for surface-mount packages.
Table 2.
Parameter
VCC to GND
Digital Inputs (ALS, LBWSET, CLKSEL)
IMODN, IMODP
Operating Temperature Range Industrial
Storage Temperature Range
Junction Temperature (TJ max)
Power Dissipation1 (W)
Lead Temperature (Soldering 10 sec)
1
Rating
4.2 V
−0.3 V to VCC + 0.3 V
VCC + 1.2 V
−40°C to +85°C
−65°C to +150°C
150°C
(TJ max − TA)/ θJA
300°C
Table 3. Thermal Resistance
Package Type
48-lead LFCSP
32-lead LFCSP
ESD CAUTION
Power consumption formulae are provided in the Power Consumption
section.
Stresses above those listed under Absolute Maximum Ratings
may cause permanent damage to the device. This is a stress
rating only; functional operation of the device at these or any
other conditions above those indicated in the operational
section of this specification is not implied. Exposure to absolute
maximum rating conditions for extended periods may affect
device reliability.
Rev. B | Page 5 of 16
θJA
25
32
Unit
°C/W
°C/W
ADN2847
Data Sheet
DIE PAD COORDINATES
2280µm
2620µm
GND2
GND2
IDTONE
VCC3
IMMON
IBMON
GND3
FAIL
ALS
CLKSEL
GND
DIE ROTATED 90° IN PACKAGE
DEGRADE GND
GND2
GND
VCC2
CLKN
IMODN
CLKP
GND2
GND1
IMODP
IMODP
DATAP
1
VCC1
IBIAS
GND
IBIAS
PAVCAP
CCBIAS
ASET
LBWSET
PSET
ERSET
IMPD
GND
IMPDMON2
IMPDMON
GND4
IMPD2
VCC4
02745-003
GND
2620µm
02745-004
ERCAP
TOP
GND2
RIGHT
DATAN
GND1
BOTTOM
GND2
LEFT
2280µm
IMODN
Figure 6. Bonding Diagram
Figure 5. Metallization Photograph
Table 4. Die Pad Coordinates1
Pad Number
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
1
Pad Name
TP1 (GND)
LBWSET
ASET
ERSET
PSET
TP2 (GND)
IMPD
IMPDMON
IMPDMON2
IMPD2
GND4
VCC4
ERCAP
PAVCAP
TP3 (GND)
VCC1
GND1
DATAN
DATAP
GND1
CLKP
CLKN
TP4 (GND)
TP5 (GND)
x[μm]
−996
−996
−996
−996
−996
−996
−996
−996
−996
−996
−996
−995
−925
−777
−606
−389
−200
−70
83
263
442
596
762
996
y[μm]
1026
853
679
506
332
159
−15
506
−361
−534
−724
−964
−1191
−1191
−1191
−1191
−1191
−1191
−1191
−1191
−1191
−1191
−1191
−1109
Pad Number
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
With the origin in the center of the die (see Figure 5).
Rev. B | Page 6 of 16
Pad Name
TP6 (GND)
CLKSEL
DEGRADE
FAIL
ALS
VCC3
GND3
IMMON
IBMON
GND2
IDTONE
GND2
GND2
VCC2
IMODN
IMODN
GND2
IMODP
IMODP
GND2
GND2
IBIAS
IBIAS
CCBIAS
x[μm]
996
996
996
996
996
996
996
996
996
996
995
995
867
713
500
396
242
88
−16
−239
−443
−633
−772
−912
y[μm]
−935
−762
−589
−415
−242
−19
251
441
614
804
993
1133
1191
1191
1191
1191
1191
1191
1191
1191
1191
1191
1191
1191
Data Sheet
ADN2847
48 CCBIAS
47 IBIAS
46 IBIAS
45 GND2
44 GND2
43 IMODP
42 IMODP
41 GND2
40 IMODN
39 IMODN
38 VCC2
37 GND2
32 CCBIAS
31 IBIAS
30 GND2
29 GND2
28 IMODP
27 GND2
26 IMODN
25 VCC2
PIN CONFIGURATIONS AND FUNCTION DESCRIPTIONS
ADN2847
ERCAP 13
PAVCAP 14
TP3 15
VCC1 16
GND1 17
DATAN 18
DATAP 19
GND1 20
CLKP 21
CLKN 22
TP4 23
TP5 24
TOP VIEW
(Not to Scale)
LBWSET 1
ASET 2
ERSET 3
PSET 4
IMPD 5
IMPDMON 6
GND4 7
VCC4 8
36 GND2
35 IDTONE
34 GND2
33 IBMON
32 IMMON
31 GND3
30 VCC3
29 ALS
28 FAIL
27 DEGRADE
26 CLKSEL
25 TP6
PIN 1
INDICATOR
ADN2847
TOP VIEW
02745-005
NOTES
1. THE EXPOSED PAD ON THE BOTTOM OF THE
PACKAGE MUST BE CONNECTED TO VCC OR
THE GND PLANE.
NOTES
1. THE EXPOSED PAD ON THE BOTTOM OF THE
PACKAGE MUST BE CONNECTED TO VCC OR
THE GND PLANE.
Figure 7. 48-Lead LFCSP
Figure 8. 32-Lead LFCSP
Table 5. Pin Function Descriptions
Pin Number
48-Lead
32-Lead
1
N/A
2
1
3
2
4
3
5
4
6
N/A
7
5
8
6
9
N/A
10
N/A
11
7
12
8
13
9
14
10
15
N/A
16
11
17
N/A
18
12
19
13
20
14
21
15
22
16
23
N/A
24
N/A
25
N/A
26
17
27
18
28
19
29
20
Mnemonic
TP1
LBWSET
ASET
ERSET
PSET
TP2
IMPD
IMPDMON
IMPDMON2
IMPD2
GND4
VCC4
ERCAP
PAVCAP
TP3
VCC1
GND1
DATAN
DATAP
GND1
CLKP
CLKN
TP4
TP5
TP6
CLKSEL
DEGRADE
FAIL
ALS
24 IBMON
23 IMMON
22 GND3
21 VCC3
20 ALS
19 FAIL
18 DEGRADE
17 CLKSEL
Description
Test Pin. In normal operation, TP1 = GND.
Select Low Loop Bandwidth.
Alarm Current Threshold Setting Pin.
Extinction Ratio Set Pin.
Average Optical Power Set Pin.
Test Pin. In normal operation, TP2 = GND.
Monitor Photodiode Input.
Mirrored Current from Monitor Photodiode.
Mirrored Current from Monitor Photodiode 2. (For use with two MPDs).
Monitor Photodiode Input 2. (For use with two MPDs).
Supply Ground.
Supply Voltage.
Extinction Ratio Loop Capacitor.
Average Power Loop Capacitor.
Test Pin. In normal operation, TP3 = GND.
Supply Voltage.
Supply Ground.
Data, Negative Differential Terminal.
Data, Positive Differential Terminal.
Supply Ground.
Data Clock Positive Differential Terminal. Used if CLKSEL = VCC.
Data Clock Negative Differential Terminal. Used if CLKSEL = VCC.
Test Pin. In normal operation, TP4 = GND.
Test Pin. In normal operation, TP5 = GND.
Test Pin. In normal operation, TP6 = GND.
Clock Select. Active = VCC. Used if data is clocked into chip.
Degrade Alarm Output.
Fail Alarm Output.
Automatic Laser Shutdown.
Rev. B | Page 7 of 16
02745-006
PIN 1
INDICATOR
ERCAP 9
PAVCAP 10
VCC1 11
DATAN 12
DATAP 13
GND1 14
CLKP 15
CLKN 16
TP1 1
LBWSET 2
ASET 3
ERSET 4
PSET 5
TP2 6
IMPD 7
IMPDMON 8
IMPDMON2 9
IMPD2 10
GND4 11
VCC4 12
ADN2847
Data Sheet
Pin Number
48-Lead
32-Lead
30
21
31
22
32
23
33
24
34
N/A
35
N/A
36
N/A
37
N/A
38
25
39
26
40
N/A
41
27
42
28
43
N/A
44
29
45
30
46
31
47
N/A
48
32
Mnemonic
VCC3
GND3
IMMON
IBMON
GND2
IDTONE
GND2
GND2
VCC2
IMODN
IMODN
GND2
IMODP
IMODP
GND2
GND2
IBIAS
IBIAS
CCBIAS
EP
EPAD
EP
Description
Supply Voltage.
Supply Ground.
Modulation Current Mirror Output.
Bias Current Mirror Output.
Supply Ground.
IDTONE. Requires external current sink to ground.
Supply Ground.
Supply Ground.
Supply Voltage.
Modulation Current Negative Output. Connect via a matching resistor to VCC.
Modulation Current Negative Output. Connect via a matching resistor to VCC.
Supply Ground.
Modulation Current Positive Output. Connect to laser diode.
Modulation Current Positive Output. Connect to laser diode.
Supply Ground.
Supply Ground.
Laser Diode Bias Current.
Laser Diode Bias Current.
Extra Laser Diode Bias. (Connected to Vcc when dc-coupled to laser diode. Connected to IBIAS
when ac-coupled to laser diode).
Exposed Pad. The exposed pad on the bottom of the package must be connected to VCC or
the GND plane.
Rev. B | Page 8 of 16
Data Sheet
ADN2847
THEORY OF OPERATION
Laser diodes have current-in to light-out transfer functions, as
shown in Figure 9. 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 slope
efficiency (LI).
ER =
PAV =
P1 + P0
2
∆P
PAV
∆I
LI =
LOOP BANDWIDTH SELECTION
∆P
∆I
P0
ITH
CURRENT
Figure 9. Laser Transfer Function
CONTROL
A monitor photodiode (MPD) is required to control the LD. The
MPD current is fed into the ADN2847 to control the power and
extinction ratio, continuously adjusting the bias current and
modulation current in response to the changing threshold
current and light-to-current slope efficiency of the laser.
The ADN2847 uses automatic power control (APC) to maintain
a constant average power over time and temperature.
The ADN2847 uses closed-loop extinction ratio control to allow
optimum setting of the extinction ratio for every device. Thus,
SONET/SDH interface standards can be met over device variation,
temperature, and laser aging. Closed-loop modulation control
eliminates the need to either overmodulate the LD or include
external components for temperature compensation. This
reduces research and development time and second sourcing
issues caused by characterizing LDs.
Average power and extinction ratio are set using the PSET pin
and the ERSET pin, respectively. Potentiometers are connected
between these pins and ground. The potentiometer RPSET is used
to change the average power. The potentiometer RERSET is used
to adjust the extinction ratio. Both PSET and ERSET are kept
1.2 V above GND.
The RPSET and RERSET potentiometers can be calculated using the
following formulas:
RPSET =
IAV is the average MPD current.
PCW is the dc optical power specified on the laser data sheet.
IMPD_CW is the MPD current at that specified PCW.
PAV is the average power required.
ER is the desired extinction ratio (ER = P1/P0).
Note that IERSET and IPSET changes from device to device; however,
the control loops determines actual values. It is not required to
know exact values for LI or MPD optical coupling.
02745-009
OPTICAL POWER
P1
P1
P0
where:
For continuous operation, the user should hardwire the LBWSET
pin high and use 1 μF capacitors to set the actual loop bandwidth.
These capacitors are placed between the PAVCAP pin and the
ERCAP pin and ground. It is important that these capacitors are
low leakage multilayer ceramics with an insulation resistance
greater than 100 GΩ or a time constant of 1000 seconds,
whichever is less.
Table 6.
Operation
Mode
Continuous
50 Mbps to
3.3 Gbps
Optimized for
2.5 Gbps to
3.3 Gbps
Recommended
PAVCAP
1 μF
Recommended
ERCAP
1 μF
Low
22 nF
22 nF
Setting LBSET low and using 22 nF capacitors results in a
shorter loop time constant (a 10× reduction over using 1 μF
capacitors and keeping LBWSET high.)
ALARMS
The ADN2847 is designed to allow interface compliance to
ITUT-G958 (11/94) section 10.3.1.1.2 (transmitter fail) and
section 10.3.1.1.3 (transmitter degrade). The ADN2847 has two
active high alarms, DEGRADE and FAIL. A resistor between
ground and the ASET pin is used to set the current at which
these alarms are raised. The current through the ASET resistor
is a ratio of 100:1 to the FAIL alarm threshold. The DEGRADE
alarm is raised at 90% of this level.
Example:
I FAIL = 50 mA so I DEGRADE = 45 mA
1.2 V
(Ω )
I AV
RERSET =
LBWSET
High
1.2 V
(Ω )
I MPD _ CW
ER − 1
× PAV
×
PCW
ER + 1
I ASET =
I FAIL 50 mA
=
= 500 μA
100
100
RASET =
1. 2 V
I ASET
=
1. 2
= 2.4 kΩ
500 μA
where the smallest valid value for RASET is 1.2 kΩ, because this
corresponds to the IBIAS maximum of 100 mA.
Rev. B | Page 9 of 16
ADN2847
Data Sheet
The laser degrade alarm, DEGRADE, is provided to give a
warning of imminent laser failure if the laser diode degrades
further or environmental conditions continue to stress the LD,
such as increasing temperature.
If the ID_TONE function is not used, the IDTONE pin should
be tied to VCC. Note that using IDTONE during transmission
can cause optical eye degradation.
The laser fail alarm, FAIL, is activated when the transmitter can
no longer be guaranteed to be SONET/SDH compliant. This
occurs when one of the following conditions arises:
Data and clock inputs are ac-coupled (10 nF capacitors are
recommended) and terminated via a 100 Ω internal resistor
between DATAP and DATAN, and also between the CLKP pin
and the CLKN pin. There is a high impedance circuit to set the
common-mode voltage that is designed to allow for maximum
input voltage headroom over temperature. It is necessary that ac
coupling is used to eliminate the need for matching between
common-mode voltages.
•
The ASET threshold is reached.
•
The ALS pin is set high. This shuts off the modulation and
bias currents to the LD, resulting in the MPD current
dropping to zero. This gives closed-loop feedback to the
system that ALS has been enabled.
DATA AND CLOCK INPUTS
ADN2847
DEGRADE is raised only when the bias current exceeds 90% of
ASET current.
DATAP
(TO FLIP-FLOPS)
DATAN
MONITOR CURRENTS
50Ω
IBMON, IMMON, IMPDMON, and IMPDMON2 are current
controlled current sources from VCC. They mirror the bias,
modulation, and MPD current for increased monitoring
functionality. An external resistor to GND gives a voltage
proportional to the current monitored.
50Ω
VREG
R
R = 2.5kΩ, DATA
R = 3kΩ, CLK
400µA TYP
02745-010
If the monitoring functions IMPDMON and IMPDMON2 are
not required, the IMPD pin and the IMPD2 pin must be
grounded and the monitor photodiode output must be
connected directly to the PSET pin.
Figure 10. AC Coupling of Data Inputs
For input signals that exceed 500 mV p-p single-ended, it is
necessary to insert an attenuation circuit as shown in Figure 11.
The ADN2847 has circuitry for a second monitor photodiode,
MPD2. The second photodiode current is mirrored to
IMPDMON2 for wavelength control purposes and is summed
internally with the first monitor photodiode current for the
power control loop. For single MPD circuits, the MPD2 pin is
tied to GND.
This enables the system designer to use the two currents to
control the wavelength of the laser diode using various optical
filtering techniques inside the laser module.
R1
R2
DATAP/CLKP
ADN2847
RIN
R3
DATAN/CLKN
NOTES
1. RIN = 100Ω = THE DIFFERENTIAL INPUT
IMPEDANCE OF THE ADN2847.
02745-011
DUAL MPD DWDM FUNCTION
(48-LEAD LFCSP ONLY)
Figure 11. Attenuation Circuit
CCBIAS
If the monitor current functions IMPDMON and IMPDMON2
are not required, then the IMPD pin and IMPD2 pin can be
grounded and the monitor photodiode output can be connected
directly to PSET.
When the laser is used in ac-coupled mode, the CCBIAS pin
and the IBIAS pin should be tied together (Figure 15). In dccoupled mode, CCBIAS should be tied to VCC.
IDTONE (48-LEAD LFCSP ONLY)
To achieve optimum eye quality, one pull-up resistor (RZ) is
necessary, as shown in both circuits in Figure 14 and Figure 15.
The recommended resistor RZ value is approximately
200 Ω ~ 500 Ω.
The IDTONE pin is supplied for fiber identification/supervisory
channels or control purposes in WDM. This pin modulates the
optical one level over a possible range of 2% of minimum IMOD
to 10% of maximum IMOD. The level of modulation is set by connecting an external current sink between the IDTONE pin and
ground. There is a gain of two from this pin to the IMOD current.
Figure 12 shows how the AD9850/AD9851 or the AD9834 can
be used with the ADN2847 to allow fiber identification.
IBIAS
AUTOMATIC LASER SHUTDOWN
The ADN2847 ALS allows compliance to ITU-T-G958 (11/94),
section 9.7. When ALS is logic high, both bias and modulation
currents are turned off. Correct operation of ALS can be confirmed
if the FAIL alarm is raised when ALS is asserted. Note that this
is the only time DEGRADE is low while FAIL is high.
Rev. B | Page 10 of 16
Data Sheet
ADN2847
REF CLOCK
20MHz TO 180MHz
CLKIN
10kHz TO 1MHz
1/2
9
1.25mA TO 20mA
AD9850/AD9851
AD9834
DDS
RSET
21
20
12
IOUT
50Ω
AD8602
35 IDTONE
0.125mA TO 2mA
LP FILTER
(DC-COUPLED)
BC550
ADN2847
IOUT
500Ω
50Ω
1/2
37.5µA TO 600µA
50µA TO 800µA
AD8602
CONTROLLER
32
BC550
IMMON
02745-012
1kΩ
1.3kΩ
Figure 12. Application Circuit to Allow Fiber Identification Using the AD9850/AD9851
ALARM INTERFACES
The FAIL and DEGRADE outputs have an internal pull-up
resistor of 30 kΩ, used to pull the digital high value to VCC.
However, the alarm can be overdriven with an external resistor
allowing alarm interfacing to non-VCC levels. Non-VCC alarm
output levels must be below the VCC used for the ADN2847.
POWER CONSUMPTION
The ADN2847 die temperature must be kept below 125°C. Both
LFCSP packages have an exposed paddle that should be connected
in such a manner that is at the same potential as the ADN2847
ground pins. The θJA for both packages is specified in the
Absolute Maximum Ratings section. Power consumption can be
calculated using
AC coupling the driver to the laser diode removes this
headroom constraint.
Caution must be taken when choosing component values for
ac coupling (see Figure 15) to ensure that the time constants
(L/R and RC) are sufficiently long for the data rate and expected
number of consecutive identical digits (CIDs). Failure to do this
can lead to pattern dependent jitter and vertical eye closure.
For designs with low series resistance, or where external
components become impractical, the ADN2847 supports direct
connection to the laser diode (see Figure 14). In this case, care
must be taken to ensure that the voltage drop across the laser
diode does not violate the minimum compliance voltage on the
IMODP pin.
OPTICAL SUPERVISOR
ICC = ICCMIN + 0.3 IMOD
P = VCC × ICC + (IBIAS × VBIAS_PIN) + IMOD (VMODP_PIN + VMODN_PIN)/2
TDIE = TAMBIENT +θJA × P
Thus, the maximum combination of IBIAS + IMOD must be
calculated, where:
The PSET and ERSET potentiometers can be replaced with a
dual-digital potentiometer, the ADN2850 (see Figure 13). The
ADN2850 provides an accurate digital control for the average
optical power and extinction ratio and ensures excellent
stability over temperature.
VCC
VCC
VCC
IMPD
VCC
ADN2847
ADN2850
SDO
CLK
LASER DIODE INTERFACING
CS
Many laser diodes designed for 2.5 Gbps operation are packaged
with an internal resistor to bring the effective impedance up to
25 Ω to minimize transmission line effects. In high current
applications, the voltage drop across this resistor combined
with the laser diode forward voltage makes direct connection
between the laser and the driver impractical in a 3 V system.
Rev. B | Page 11 of 16
RZ
IBIAS
DAC1
PSET
DAC2
ERSET
CLK
IDTONE
Rx
IMODP
DATAN
SDI
DATAP
Tx
CS
DATAP
DATAN
IDTONE
Figure 13. Application Using the ADN2850 a Dual 10-Bit Digital
Potentiometer with an Extremely Low Temperature Coefficient
as an Optical Supervisor
02745-013
ICCMIN = 50 mA (typical value of ICC provided in the
Specifications section)
IBIAS = IMOD = 0
TDIE = die temperature
TAMBIENT = ambient temperature
VBIAS_PIN = voltage at IBIAS pin
VMODP_PIN = average voltage at IMODP pin
VMODN_PIN = average voltage at IMODN pin
ADN2847
Data Sheet
FAIL
DEGRADE
ALS
1kΩ
VCC
1.5kΩ
1.5kΩ
25
GND
CLKSEL
FAIL
DEGRADE
ALS
VCC3
GND3
IMMON
GND2
IBMON
GND2
GND
VCC2
IMODN
CLKP
GND2
GND1
GND2
VCC1
GND
IBIAS
PAVCAP
1
VCC4
ERCAP
GND4
CCBIAS
IMPD2
IBIAS
IMPDMON2
VCC
48
GND1
ERSET
10µH
GND2
ASET
RZ
DATAN
LBWSET
VCC
12
**
**
10nF
10nF
10nF
DATAP
ADN2847
IMODP
GND
*
GND
1.5kΩ
10nF
CLKN
CLKP
DATAP
DATAN
22nF
22nF
13
VCCs SHOULD HAVE BYPASS CAPACITORS AS
CLOSE AS POSSIBLE TO THE ACTUAL SUPPLY PINS
ON THE ADN2847 AND THE LASER DIODE USED.
CONSERVATIVE DECOUPLING WOULD INCLUDE
100pF CAPACITORS IN PARALLEL WITH 10nF
CAPACITORS.
VCC
LD = LASER DIODE
MPD = MONITOR PHOTODIODE
100nF
100nF
100nF
GND
NOTES
* DESIGNATES COMPONENTS THAT NEED TO BE OPTIMIZED FOR THE TYPE OF LASER USED.
** FOR DIGITAL PROGRAMMING, THE ADN2850 OR THE ADN2860 OPTICAL SUPERVISOR CAN BE USED.
Figure 14. DC-Coupled 3.3 Gbps Test Circuit, Data Not Clocked
Rev. B | Page 12 of 16
100nF
10µF
02745-014
IMODP
*
IMPDMON
*
CLKN
IMPD
LD
IMODN
GND
*
VCC
24
GND
PSET
VCC
MPD
GND2
37
IDTONE
36
Data Sheet
ADN2847
FAIL
DEGRADE
ALS
1kΩ
VCC
VCC
*
1.5kΩ
*
GND
CLKSEL
DEGRADE
ALS
FAIL
VCC3
GND3
IBMON
IMMON
GND2
GND
VCC2
IMODN
CLKP
GND2
GND1
IMODP
GND2
VCC1
GND
IBIAS
PAVCAP
GND
1
ERCAP
VCC4
CCBIAS
48
IMPD2
IBIAS
GND4
1µH
GND1
IMPDMON2
RZ
GND2
IMPDMON
VCC
DATAN
ERSET
*
IMODP
ASET
*
GND
12
**
1.5kΩ
**
10nF
10nF
10nF
DATAP
ADN2847
LBWSET
*
CLKN
IMPD
*
IMODN
GND
LD
24
GND
PSET
VCC
MPD
25
GND2
37
*
1.5kΩ
36
*
GND2
*
IDTONE
*
10nF
CLKN
CLKP
DATAP
DATAN
1µF
1µF
13
VCCs SHOULD HAVE BYPASS CAPACITORS AS
CLOSE AS POSSIBLE TO THE ACTUAL SUPPLY PINS
ON THE ADN2847 AND THE LASER DIODE USED.
CONSERVATIVE DECOUPLING WOULD INCLUDE
100pF CAPACITORS IN PARALLEL WITH 10nF
CAPACITORS.
VCC
LD = LASER DIODE
MPD = MONITOR PHOTODIODE
100nF
100nF
100nF
100nF
10µF
02745-015
GND
NOTES
* DESIGNATES COMPONENTS THAT NEED TO BE OPTIMIZED FOR THE TYPE OF LASER USED.
** FOR DIGITAL PROGRAMMING, THE ADN2850 OR THE ADN2860 OPTICAL SUPERVISOR CAN BE USED.
02745-016
02745-017
Figure 15. AC-Coupled 50 Mbps to 3.3 Gbps Test Circuit, Data Not Clocked
Figure 16. 2.5 Gbps Optical Eye at 25°C. Average Power = 0 dBm,
Extinction Ratio = 10 dB, PRBS 31 Pattern. Eye Obtained Using a DFB Laser.
Figure 17. 2.5 Gbps Optical Eye at 85°C. Average Power = 0 dBm,
Extinction Ratio = 10 dB, PRBS 31 Pattern. Eye Obtained Using a DFB Laser.
Rev. B | Page 13 of 16
ADN2847
Data Sheet
OUTLINE DIMENSIONS
0.30
0.25
0.18
32
25
0.50
BSC
17
TOP VIEW
0.80
0.75
0.70
8
16
9
BOTTOM VIEW
0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.20 REF
SEATING
PLANE
3.25
3.10 SQ
2.95
EXPOSED
PAD
0.50
0.40
0.30
PIN 1
INDICATOR
1
24
0.25 MIN
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
112408-A
PIN 1
INDICATOR
5.10
5.00 SQ
4.90
COMPLIANT TO JEDEC STANDARDS MO-220-WHHD.
Figure 18. 32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
5 mm × 5 mm Body, Very Very Thin Quad
(CP-32-7)
Dimensions shown in millimeters
0.30
0.23
0.18
PIN 1
INDICATOR
48
37
36
1
0.50
BSC
TOP VIEW
0.80
0.75
0.70
SEATING
PLANE
0.45
0.40
0.35
5.20
5.10 SQ
5.00
EXPOSED
PAD
12
25
24
13
BOTTOM VIEW
0.05 MAX
0.02 NOM
COPLANARITY
0.08
0.20 REF
0.25 MIN
FOR PROPER CONNECTION OF
THE EXPOSED PAD, REFER TO
THE PIN CONFIGURATION AND
FUNCTION DESCRIPTIONS
SECTION OF THIS DATA SHEET.
COMPLIANT TO JEDEC STANDARDS MO-220-WKKD.
Figure 19. 48-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
7 mm × 7 mm Body, Very Very Thin Quad
(CP-48-4)
Dimensions shown in millimeters
Rev. B | Page 14 of 16
PIN 1
INDICATOR
112408-B
7.00
BSC SQ
Data Sheet
ADN2847
ORDERING GUIDE
Model 1
ADN2847ACPZ-32
ADN2847ACPZ-32-RL
ADN2847ACPZ-32-RL7
ADN2847ACPZ-48
1
Temperature Range
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
−40°C to +85°C
Package Description
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
32-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
48-Lead Lead Frame Chip Scale Package [LFCSP_WQ]
Z = RoHS Compliant Part.
Rev. B | Page 15 of 16
Package Option
CP-32-7
CP-32-7
CP-32-7
CP-48-4
ADN2847
Data Sheet
NOTES
©2003–2012 Analog Devices, Inc. All rights reserved. Trademarks and
registered trademarks are the property of their respective owners.
D02745-0-3/12(B)
Rev. B | Page 16 of 16
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