Maxim MAX3867ECM, MAX3867E-D Datasheet

General Description

The MAX3867 is a complete, single +3.3V laser driver
for SDH/SONET applications up to 2.5Gbps. The
device accepts differential PECL data and clock inputs
and provides bias and modulation currents for driving a
laser. The synchronizing input latch can be bypassed if
a clock signal is not available.

An automatic power control (APC) feedback loop is
incorporated to maintain a constant average optical
power over temperature and lifetime. The wide modula­tion current range of 5mA to 60mA and bias current of
1mA to 100mA are easy to program, making this prod­uct ideal for use in various SDH/SONET applications.

The MAX3867 also provides enable control, a program­mable slow-start circuit to set the laser turn-on delay,
and a failure-monitor output to indicate when the APC
loop is unable to maintain the average optical power.
The MAX3867 is available in a small 48-pin TQFP pack­age as well as dice.

Applications

SONET/SDH Transmission Systems
Add/Drop Multiplexers
Digital Cross-Connects
Section Regenerators

2.5Gbps Optical Transmitters

Features

♦ Single +3.3V or +5V Power Supply
♦ 62mA Supply Current at +3.3V
♦ Programmable Modulation Current from

5mA to 60mA

♦ Programmable Bias Current from 1mA to 100mA
♦ Rise/Fall Time < 90ps
♦ Automatic Average Power Control with Failure

Monitor

♦ Complies with ANSI, ITU, and Bellcore

SDH/SONET Specifications

♦ Enable Control

*

Dice are designed to operate over this range, but are tested and

guaranteed at TA= +25°C only. Contact factory for availability.

Ordering Information

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver

with Automatic Power Control

________________________________________________________________

Maxim Integrated Products

1

EVALUATION KIT

AVAILABLE

124Ω 124Ω

SERIALIZER

WITH

CLOCK GEN.

124Ω

20Ω

LD

25Ω

+3.3V

+3.3V

0.056µF

1000pF

BIASMAX

LATCH

ENABLE

FAIL

MODSET

APCSET

APCFILT

CLK-

CLK+

DATA-

DATA+

*FERRITE
BEAD

OUT+

BIAS

MD

OUT-

CAPC

124Ω

84.5Ω 84.5Ω 84.5Ω84.5Ω

MAX3867

MAX3890

Typical Operating Circuit

19-4769; Rev 0a; 9/98

Pin Configuration appears at end of data sheet.

PART

MAX3867ECM
MAX3867E/D -40°C to +85°C

-40°C to +85°C

TEMP. RANGE PIN-PACKAGE

48 TQFP
Dice*

For free samples & the latest literature: http://www.maxim-ic.com, or phone [phone].
For small orders, phone [phone].

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control

2 _______________________________________________________________________________________

IMD= 1mA
IMD= 18µA

90

ENABLE = low (Note 4)

APC open loop, I

BIAS

= 1mA

(Note 3)

900

(Note 2)

(Note 5)

Sourcing 50µA

(Note 6)

APC open loop, I

BIAS

= 100mA

APC open loop
Figure 1

PECL compatible

Sinking 100µA

CONDITIONS

%

-15 15

Monitor-Diode Bias Absolute
Accuracy

ppm/°C

-480 50 480

Monitor-Diode Bias Setpoint
Stability

µA

18 1000

I

MD

Monitor-Diode DC Current
Range

V

1.5

Monitor-Diode Reverse Bias
Voltage

V

0.1 0.44

TTL Output Low Voltage FAIL

µA

100

I

BIAS-OFF

Bias Off Current

mA

1 100

I

BIAS

mA

62 105

I

CC

Supply Current
Bias Current Range

V

2.4 VCC- 0.3 V

CC

TTL Output High Voltage FAIL

V

0.8

TTL Input Low Voltage
(ENABLE, LATCH)

V

2.0

TTL Input High Voltage
(ENABLE, LATCH)

µA

-1 10

I

IN

Clock and Data Input Current

ppm/°C

230

Bias-Current Stability

%

-15 15

(Note 5)Bias-Current Absolute Accuracy

mVp-p

200 1600

V

ID

Differential Input Voltage

V

VCC- VCC- VCC-

1.49 1.32 V

ID

/4

V

ICM

Common-Mode Input Voltage

UNITSMIN TYP MAXSYMBOLPARAMETER

DC ELECTRICAL CHARACTERISTICS

(VCC= +3.14V to +5.5V, TA= -40°C to +85°C. Typical values are at VCC= +3.3V, I

MOD

= 30mA, I

BIAS

= 60mA, and TA= +25°C,

unless otherwise noted.) (Note 1)

Stresses beyond those listed under “Absolute Maximum Ratings” may cause permanent damage to the device. These are stress ratings only, and functional
operation of the device at these or any other conditions beyond those indicated in the operational sections of the specifications is not implied. Exposure to
absolute maximum rating conditions for extended periods may affect device reliability.

Note 1: Characteristics at -40°C guaranteed by design and characterization. Dice are tested at TA= +25°C only.
Note 2: Tested at R

MODSET

= 2.49kΩ, R

BIASMAX

= 1.69kΩ, excluding I

BIAS

and I

MOD

.

Note 3: Voltage on BIAS pin is (V

CC

- 1.6V).

Note 4: Both the bias and modulation currents will be switched off if any of the current set pins are grounded.
Note 5: Accuracy refers to part-to-part variation.
Note 6: Assuming that the laser to monitor-diode transfer function does not change with temperature.

Supply Voltage, V

CC

............................................. -0.5V to +7.0V

Current into BIAS ...........................................-20mA to +150mA

Current into OUT+, OUT-................................-20mA to +100mA

Current into MD.....................................................-5mA to +5mA

Voltage at DATA+, DATA-, CLK+, CLK-,

ENABLE, LATCH, FAIL, SLWSTRT.........-0.5V to (V

CC

+ 0.5V)

Voltage at APCFILT, CAPC, MODSET,

BIASMAX, APCSET ...........................................-0.5V to +3.0V

Voltage at OUT+, OUT-.............................+1.5V to (V

CC

+ 1.5V)

Voltage at BIAS.........................................+1.0V to (V

CC

+ 0.5V)

Current into FAIL ...............................................-10mA to +30mA

Continuous Power Dissipation (T

A

= +85°C)

TQFP (derate 20.8mW/°C above +85°C)...................1354mW

Storage Temperature Range.............................-65°C to +165°C

Operating Junction Temperature Range...........-55°C to +150°C

Processing Temperature (die).........................................+400°C

Lead Temperature (soldering, 10sec).............................+300°C

ABSOLUTE MAXIMUM RATINGS

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver

with Automatic Power Control

_______________________________________________________________________________________ 3

AC ELECTRICAL CHARACTERISTICS

(V

CC

= +3.14V to +5.5V, load as shown in Figure 2, TA= -40°C to +85°C. Typical values are at VCC= +3.3V, I

MOD

= 30mA, and TA=

+25°C.) (Note 7)

Note 7: AC characteristics are guaranteed by design and characterization.
Note 8: Measured with 622Mbps 0-1 pattern, LATCH = high.
Note 9: PWD = (wider pulse - narrower pulse) / 2.
Note 10: See

Typical Operating Characteristics

for worst-case distribution.

I

MOD

= 5mA

250

79

LATCH = high, Figure 3

LATCH = high, Figure 3

20% to 80% (Note 8)

ps

69

(Note 8)

20% to 80% (Note 8)

ENABLE = low (Note 4)
I

MOD

= 60mA

(Note 6)

Jitter BW = 12kHz to 20MHz, 0-1 pattern

(Notes 8, 9)

CONDITIONS

t

R

Output Rise Time ps

ps

p-p

720

Jitter Generation

ps

950

PWDPulse-Width Distortion

mA

560

I

MOD

Modulation-Current Range

ps

100

t

H

ps

100

t

SU

Input Latch Setup Time
Input Latch Hold Time

bits

80

Maximum Consecutive Identical
Digits

ns

250

Enable/Start-Up Delay

%

±15

Output Aberrations

79

t

F

Output Fall Time

µA

200

I

MOD-OFF

Modulation-Off Current

ppm/°C

-480 -50 480

Modulation-Current Stability

%

-15 15

Modulation-Current Absolute
Accuracy

88 (Note 10)

UNITSMIN TYP MAXSYMBOLPARAMETER

MAX3867ECM
MAX3867C/D
MAX3867ECM
MAX3867C/D

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control

4 _______________________________________________________________________________________

DATA+

DATA-

(DATA+) - (DATA-)

I

OUT

+

100mV MIN
800mV MAX

200mVp-p MIN

1600mVp-p MAX

I

MOD

Figure 1. Required Input Signal and Output Polarity

CLK

DATA

t

CLK

= 402ps

t

SU

t

H

Figure 3. Setup/Hold Time Definition

0.056µF

0.5pF

*

* TO COMPENSATE PACKAGE LEADS, NOT USED FOR DIE.

OUT+

BIAS

OUT-

A

B

A

A, B ARE SMD FERRITE BEADS
B = BLM11A601S MURATA ELECTRONICS
A = BLM21A102S MURATA ELECTRONICS

B

V

CC

50Ω

15Ω

OSCILLOSCOPE

50Ω

25Ω

0.056µF

V

CC

MAX3867

Figure 2. Output Termination for Characterization

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver

with Automatic Power Control

_______________________________________________________________________________________

5

26mV

/div

50ps/div

ELECTRICAL EYE DIAGRAM

MAX3867-04a

PATTERN = 213 - 1 + 80 CID
I

MOD

= 30mA

48-TQFP

0.010

0.012

0.014

0.016

0.018

0.020

0.022

41811 25 32 39 46 53 60

RANDOM JITTER vs. I

MOD

MAX3867 toc05

I

(mA)

RANDOM JITTER (UIp-p)

JITTER BW = 12kHz to 20MHz
1-0 PATTERN

55mV

/div

50ps/div

ELECTRICAL EYE DIAGRAM

MAX3867-05a

PATTERN = 213 - 1 + 80 CID
I

MOD

= 60mA

48-TQFP

120

0

110

100

300

I

BIASMAX

vs. R

BIASMAX

MAX3867-06

R

BIASMAX

(kΩ)

I

BIASMAX

(mA)

40

80

100

20

60

100

0

1 10 100

I

MOD

vs. R

MODSET

20
10

MAX3867-07

R

MODSET

(kΩ)

I

MOD

(mA)

40
30

60

70

50

80

90

1.2

0

0.1 1 10 100

IMD vs. R

APCSET

0.4

MAX3867-08

R

APCSET

(kΩ)

I

MD

(mA)

0.6

0.8

1.0

1.1

0.3

0.2

0.1

0.5

0.7

0.9

Typical Operating Characteristics

(V

CC

= +3.3V, load as shown in Figure 2, TA= +25°C, unless otherwise noted.)

EYE DIAGRAM

(2.488Gbps, 1300nm FP LASER,

1.87GHz FILTER, 48-TQFP)

MAX3867-01

50ps/div

0

20

10

40

30

50

60

80 88

48-TQFP
I

MOD

= 30mA

MEAN = 88ps
σ = 3.0ps

92 9684100

TYPICAL DISTRIBUTION OF FALL TIME

MAX3867-02a

FALL TIME (ps)

PERCENT IN UNITS (%)

0

20
15
10

5

30
25

40
35

106 108 112

48-TQFP
I

MOD

= 30mA
VCC = +3.14V
T

A

= +85°C

MEAN = 111.6ps
σ = 2.9ps

114 116 118

110

120 122

DISTRIBUTION OF FALL TIME

(WORST-CASE CONDITIONS)

MAX3867-03a

FALL TIME (ps)

PERCENT IN UNITS (%)

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control

6 _______________________________________________________________________________________

0

30
20
10

40

50

60

70

80

90

100

-40 10-15 35 60 85

SUPPLY CURRENT vs. TEMPERATURE

(EXCLUDE I

BIAS

, I

MOD

, 25Ω LOAD)

MAX3867-09

TEMPERATURE (°C)

I

CC

(mA)

VCC = +5V

VCC = +3.3V

I

MOD

= 30mA

I

BIAS

= 45mA

0.

5

15

10

20

25

52010 30 40 50 60

PULSE-WIDTH DISTORTION

vs. I

MOD

MAX3867-10

I

MOD

(mA)

PWD (ps)

V

CC

= +5V

VCC = +3.3V

Pin Description

Typical Operating Characteristics (continued)

(V

CC

= +3.3V, load as shown in Figure 2, TA= +25°C, unless otherwise noted.)

NAME FUNCTION

1, 42, 45 GND2 Ground for internal reference

2, 7, 12, 15, 16, GND1 Ground for digital circuits

PIN

3, 6, 8, 11, 18 VCC1 Power supply for digital circuits

4 DATA+ Positive PECL Data Input

13 LATCH TTL/CMOS Latch Input. High for latched data, low for direct data.

10 CLK- Negative PECL Clock Input. Leave unconnected if latch function is not used.

9 CLK+ Positive PECL Clock Input. Connect to VCCif latch function is not used.

5 DATA- Negative PECL Data Input

22 APCFILT Connect a capacitor (C

APCFILT

= 0.1µF) from this pad to ground to filter the APC noise.

21, 26, 28, 31, 39,

41, 43

N.C. No Connection. Leave unconnected.

19

FAIL

TTL/CMOS output. Indicates APC failure when low.

17 SLWSTRT

A capacitor from this pad to ground delays the turn-on time of laser bias and modulation
currents.

14 ENABLE

TTL/CMOS Enable Input. High for normal operation, low to disable laser bias and modulation
currents.

20, 23, 33 GND4 Ground for output circuitry
24, 27, 32 VCC4 Power Supply for output circuitry

_______________Detailed Description

The MAX3867 laser driver consists of two main parts: a
high-speed modulation driver and a laser-biasing block
with Automatic Power Control (APC). The circuit design
is optimized for both high-speed and low-voltage
(+3.3V) operation. To minimize the pattern-dependent
jitter of the input signal at speeds as high as 2.5Gbps,
the device accepts a differential PECL clock signal for
data retiming. When LATCH is high, the input data is
synchronized by the clock signal. When LATCH is low,
the input data is directly applied to the output stage.

The output stage is composed of a high-speed differential
pair and a programmable modulation current source.
Since the modulation output drives a maximum current
of 60mA into the laser with an edge speed of 100ps,
large transient voltage spikes can be generated due to
the parasitic inductance. These transients and the laser
forward voltage leave insufficient headroom for the
proper operation of the laser driver if the modulation
output is DC-coupled to the laser diode. To solve this
problem, the MAX3867’s modulation output is designed
to be AC-coupled to the cathode of a laser diode. An
external pull-up inductor is necessary to DC-bias the
modulation output at VCC. Such a configuration isolates
laser forward voltage from the output circuitry and

allows the output at OUT+ to swing above and below
the supply voltage VCC. A simplified functional diagram
is shown in Figure 4.

The MAX3867 modulation output is optimized for driv­ing a 25Ω load; the minimum required voltage at OUT+
is 2.0V. Modulation current swings of 80mA are possi­ble, but due to minimum power supply and jitter
requirements at 2.5Gbps, the specified maximum mod­ulation current is limited to 60mA. To interface with the
laser diode, a damping resistor (RD) is required for
impedance matching. An RC shunt network is also nec­essary to compensate for the laser-diode parasitic
inductance, thereby improving the optical output aber­rations and duty-cycle distortion.

At the data rate of 2.5Gbps, any capacitive load at the
cathode of a laser diode will degrade the optical output
performance. Since the BIAS output is directly connected
to the laser cathode, minimize the parasitic capacitance
associated with this pin by using an inductor to isolate the
BIAS pin from the laser cathode.

Automatic Power Control

To maintain constant average optical power, the
MAX3867 incorporates an APC loop to compensate for
the changes in laser threshold current over temperature
and lifetime. A back-facet photodiode mounted in the

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver

with Automatic Power Control

_______________________________________________________________________________________ 7

NAME FUNCTIONPIN

25 BIAS Laser Bias Current Output
29 OUT+ Positive Modulation-Current Output. I

MOD

flows through this pad when input data is high.

37 VCC3 Power Supply for APC

34, 36, 40 GND3 Ground for APC

35 MD

Monitor Diode Input. Connect this pad to a monitor photodiode anode. A capacitor to ground
is required to filter high-speed AC monitor photocurrent.

30 OUT- Negative Modulation-Current Output. I

MOD

flows through this pad when input data is low.

48 VCC2 Power Supply for internal reference

47 BIASMAX

A resistor connected from this pad to ground sets the maximum bias current. The APC
function can subtract from this maximum value, but can not add to it.

46 MODSET A resistor connected from this pad to ground sets the desired modulation current.

44 APCSET

A resistor connected from this pad to ground sets the desired average optical power.
Connect 100kΩ from this pad to ground if APC is not used.

38 CAPC

A capacitor connected from this pad to ground controls the dominant pole of the APC feed­back loop. (C

APC

= 0.1µF)

Pin Description (continued)

MAX3867

laser package is used to convert the optical power into
a photocurrent. The APC loop adjusts the laser bias
current so that the monitor current is matched to a ref­erence current set by R

APCSET

. The time constant of
the APC loop is determined by an external capacitor
(C

APC

). To eliminate the pattern-dependent jitter asso­ciated with the APC loop-time constant, and to guaran­tee loop stability, the recommended value for C

APC

is

0.1µF.
When the APC loop is functioning, the maximum allow-

able bias current is set by an external resistor, R

BIASMAX

.
An APC failure flag (FAIL) is set low when the bias current
can no longer be adjusted to achieve the desired aver-

age optical power. To filter out the APC loop noise, use
an external capacitor at APCFILT with a recommended
value of 0.1µF.

APC closed-loop operation requires the user to set three
currents with external resistors connected between
ground and BIASMAX, MODSET, and APCSET. Detailed
guidelines for these resistor settings are described in
the

Design Procedure

section.

Open-Loop Operation

If necessary, the MAX3867 is fully operational without
APC. In this case, the laser current is directly set by two
external resistors connected from ground to BIASMAX

+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control

8 _______________________________________________________________________________________

LATCH

C

D

C

F

R

F

V

CC

1000pF

I

MD

R

APCSET

R

BIASMAX

R

MODSET

APCSET

CAPC

C

APC

BIASMAX

MD

MODSET

FAIL

BIAS

R

D

25Ω

I

MOD

I

BIAS

L

P

L

P

V

CC

MUX

DATA

CLK

0
1

ENABLE

OUT+

OUT-

DQ

172X

FAILURE

DETECTOR

40X

5X

MAX3867

Figure 4. Functional Diagram

and MODSET. See the

Design Procedure

section for

more details on open-loop operation.

Optional Data Input Latch

To minimize input data pattern-dependent jitter, the dif­ferential clock signal should be connected to the data
input latch, which is selected by an external LATCH
control. If LATCH is high, the input data is retimed by
the rising edge of CLK+. If LATCH is low, the input data
is directly connected to the output stage. When this
latch function is not used, connect CLK+ to VCCand
leave CLK- unconnected.

Enable Control

The MAX3867 incorporates a laser driver enable func­tion. When ENABLE is low, both the bias and modulation
currents are off. The typical laser enable time is 250ns
and the typical disable time is 25ns.

Slow-Start

For laser safety reasons, the MAX3867 incorporates a
slow-start circuit which provides a programmable delay
time for enabling a laser diode. An external capacitor
(C

SLWSTRT

) connected from this pad to ground pro-

grams the delay by the equation:

t

ENABLE

≅ 100kΩ · (C

SLWSTRT

+ 2.5pF)

APC Failure Monitor

The MAX3867 provides an APC failure monitor
(TTL/CMOS) to indicate an APC loop tracking failure.
FAIL is set low when the APC loop can no longer adjust
the bias current to maintain the desired monitor current.

Short-Circuit Protection

The MAX3867 provides short-circuit protection for the
modulation, bias and monitor current sources. If either
BIASMAX, MODSET, or APCSET is shorted to ground,
the bias and modulation output will be turned off.

Design Procedure

When designing a laser transmitter, the optical output is
usually expressed in terms of average power and extinc­tion ratio. Table 1 gives the relationships that are helpful
in converting between the optical average power and the
modulation current. These relationships are valid if the
average duty cycle of optical waveform is 50%

Programming the Modulation Current

For a given laser power P

AVE

, slope efficiency η, and
extinction ration re, the modulation current can be calcu­lated by Table 1. Refer to the I

MOD

vs. R

MODSET

graph

in the

Typical Operating Characteristics

and select the

value of R

MODSET

that corresponds to the required cur-

rent at +25°C.

Programming the Bias Current

When using the MAX3867 in open-loop operation, the
bias current is determined by the R

BIASMAX

resistor. To
select this resistor, determine the required bias current
at +25°C. Refer to the I

BIASMAX

vs. R

BIASMAX

graph in

the

Typical Operating Characteristics

and select the

value of R

BIASMAX

that corresponds to the required

current at +25°C.
When using the MAX3867 in closed-loop operation, the

R

BIASMAX

resistor sets the maximum bias current avail­able to the laser diode over temperature and life. The
APC loop can subtract from this maximum value but
cannot add to it. Refer to the I

BIASMAX

vs. R

BIASMAX

graph in the

Typical Operating Characteristics

and

select the value of R

BIASMAX

that corresponds to the

end-of-life bias current at +85°C.

Programming the APC Loop

When the MAX3867’s APC feature is used, program the
average optical power by adjusting the APCSET resistor.
To select this resistor, determine the desired monitor cur­rent to be maintained over temperature and life. Refer to
the IMDvs. R

APCSET

graph in the

Typical Operating

Characteristics

and select the value of R

APCSET

that cor-

responds to the required current.

Interfacing with the Laser Diode

To minimize optical output aberrations due to the laser
parasitic inductance, an RC shunt network is required
(Figure 4). If RLrepresents the laser diode resistance,
the recommended total resistance for RD+ RLis 25Ω.
Starting values for coaxial lasers are RF= 75Ω and
CF= 3.3pF. RFand CFshould be experimentally
adjusted until the optical output waveform is optimized.
A bypass capacitor should also be placed as close to
the laser anode as possible, for the best performance.

Pattern-Dependent Jitter (PDJ)

When transmitting NRZ data with long strings of con­secutive identical digits (CID), LF droop can occur and
contribute to pattern-dependent jitter. To minimize this

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver

with Automatic Power Control

_______________________________________________________________________________________ 9

PARAMETER SYMBOL RELATION

Average Power P

AVE

P

AVE

= (P0+ P1) / 2

Extinction Ratio r

e

re= P1/ P

0

Optical Power High P

1

P1= 2P

AVE

· re/ (re+ 1)

Optical Power Low P

0

P0= 2P

AVE

/ (re+ 1)

Optical Amplitude Pp-p Pp-p = 2P

AVE(re

- 1) / (re+ 1)

Laser Slope
Efficiency

η

η = Pp-p / I

MOD

Modulation Current I

MOD

I

MOD

= Pp-p /η

Table 1. Optical Power Definition

MAX3867

pattern-dependent jitter, three external components
must be properly chosen: capacitor C

APC

, which domi­nates the APC loop time constant; pull-up inductor LP;
and AC-coupling capacitor CD.

To filter out noise effects and guarantee loop stability,
the recommended value for C

APC

is 0.1µF. This results
in an APC loop bandwidth of 10kHz or a time constant
of 16µs. As a result, the pattern-dependent jitter associ­ated with an APC loop time constant can be ignored.

The time constant associated with the output pull-up
inductor (LP), and the AC-coupling capacitor (CD), will
also impact the pattern-dependent jitter. For such a
second-order network, the PDJ due to the low frequen­cy cutoff will be dominated by LP. For a data rate of

2.5Gbps, the recommended value for CDis 0.056µF.
During the maximum CID period t,it is recommended
to limit the peak voltage droop to less than 12% of the
average (6% of the amplitude). The time constant can
be estimated by:

12% = 1 - e

-t

/

τ

L

P

τ

LP

= 7.8t

If τLP= LP/25Ω, and t = 100UI = 40ns, then LP= 7.8µH.
To reduce the physical size of this element (LP), use of
SMD ferrite beads is recommended (Figure 2).

Input Termination Requirement

The MAX3867 data and clock inputs are PECL-compat­ible. However, it is not necessary to drive the MAX3867
with a standard PECL signal. As long as the specified
common-mode voltage and the differential voltage
swings are met, the MAX3867 will operate properly.

Calculate Power Consumption

The junction temperature of the MAX3867 dice must be
kept below +150°C at all times. The total power dissipa­tion of the MAX3867 can be estimated by the following:

P = V

CC

· V

CC

+ (VCC- Vf) · I

BIAS

+ I

MOD(VCC

- 25Ω · I

MOD

/ 2)

where I

BIAS

is the maximum bias current set by R

BIAS-

MAX

, I

MOD

is the modulation current, and Vfis the typi-

cal laser forward voltage.

Junction temperature = P(W) · 48 (°C/W)

Applications Information

The following is an example of how to set up the
MAX3867.

Select Laser

A communication-grade laser should be selected for

2.488Gbps applications. Assume the laser output aver­age power is P

AVE

= 0dBm, minimum extinction ratio is
re= 6.6 (8.2dB), the operating temperature is -40°C to
+85°C, and the laser diode has the following character­istics:

Wavelength: λ = 1.3µm
Threshold Current: ΙTH= 22mA at +25°C
Threshold Temperature

Coefficient: βTH= 1.3%/°C
Laser to Monitor Transfer: ρ

MON

= 0.2A/W

Laser Slope Efficiency: η = 0.05mW/mA

at +25°C

Determine R

APCSET

The desired monitor diode current is estimated by
IMD= P

AVE

·

ρ

MON

= 200µA. The IMDvs. R

APCSET

graph in the

Typical Operating Characteristics

shows

that R

APCSET

should be 6.0kΩ.

Determine R

MODSET

To achieve a minimum extinction ratio (re) of 6.6dB over
temperature and lifetime, calculate the required extinc­tion ratio at 25°C. Assuming re= 20, the peak-to-peak
optical power P

p-p

= 1.81mW according to Table 1. The
required modulation current is 1.81(mW) / 0.05(mW/mA)
= 36.2mA. The I

MOD

vs. R

MODSET

graph in the

Typical

Operating Characteristics

shows that R

MODSET

should

be 4.8kΩ.

Determine R

BIASMAX

Calculate the maximum threshold current (I

TH(MAX)

) at

TA= +85°C and end of life. Assuming I

TH(MAX)

=

50mA, the maximum bias current should be:

I

BIASMAX

= I

TH(MAX)

+ I

MOD

/2

In this example, I

BIASMAX

= 68.1mA. The I

BIASMAX

vs.

R

BIASMAX

graph in the

Typical Operating Characteristics

shows that R

BIASMAX

should be 3.2kΩ.

+3.3V, 2.5Gbps SDH/SONET Laser Driver
with Automatic Power Control

10 ______________________________________________________________________________________

Modulation Current More than 60mA

At +5V power supply, the headroom voltage for the
MAX3867 is significantly improved. In this case, it is
possible to achieve a modulation current of more than
60mA with AC-coupling, if the junction temperature is
kept below 150°C. The MAX3867 can also be DC-cou­pled to a laser diode when operating at +5V supply; the
voltage at OUT+ should be ≥2.0V for proper operation.

Wire Bonding Die

For high current density and reliable operation, the
MAX3867 uses gold metalization. Make connections to
the die with gold wire only, using ball-bonding tech­niques. Wedge bonding is not recommended. Die-pad
size is 4 mils (100µm) square, and die thickness is 12
mils (300µm) mils.

Layout Considerations

To minimize inductance, keep the connections between
the MAX3867 output pins and LD as close as possible.
Optimize the laser diode performance by placing a
bypass capacitor as close as possible to the laser
anode. Use good high-frequency layout techniques
and multilayer boards with uninterrupted ground planes
to minimize EMI and crosstalk.

Laser Safety and IEC 825

Using the MAX3867 laser driver alone does not ensure
that a transmitter design is compliant with IEC 825. The
entire transmitter circuit and component selections must
be considered. Each customer must determine the level
of fault tolerance required by their application, recogniz­ing that Maxim products are not designed or authorized
for use as components in systems intended for surgical
implant into the body, for applications intended to sup­port or sustain life, or for any other application where the
failure of a Maxim product could create a situation
where personal injury or death may occur.

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver

with Automatic Power Control

______________________________________________________________________________________ 11

Pin Configuration Chip Topography

4243444546 383940

41

47

16

19

21

20

22

23

17 1814

15

2
3
4
5
6
7
8

9
10
11

26

27

28

29

30

31

32

33

34

35

VCC1

GND1

BIASMAX

MAX3867

TQFP

TOP VIEW

MODSET

GND2

APCSET

N.C.

GND2

N.C.

GND3

N.C.

CAPC37VCC3

ENABLE

SLWSTRT

GND1

FAIL

VCC1

N.C.

GND4

GND4

APCFILT

24

VCC4

MD
GND3
GND4
VCC4
N.C.
OUT­OUT+
N.C.
VCC4
N.C.

25

BIAS

12

GND1

CLK-

CLK+

VCC1

GND1

VCC1

DATA-

DATA+

VCC1

GND1

1

36

GND3

GND2

48

13

VCC2

LATCH

LATCH

GND1

VCC1 CLK+ GND1 DATA- VCC1

CLK- VCC1 VCC1 DATA+ GND1

ENABLE

GND1
GND1

SLWSTRT

VCC1

FAIL

GND4

N.C.

APCFILT

GND4

VCC4

MDGND4N.C.OUT+VCC4

OUT-N.C. N.C. GND3VCCA

BIAS

VCC2

GND2

BIASMAX
MODSET

GND2
APCSET
N.C.

GND2
N.C.

GND3
N.C.

CAPC
VCC3
GND3

0.083"

(2.108mm)

0.070"

(1.778mm)

MAX3867

+3.3V, 2.5Gbps SDH/SONET Laser Driver

with Automatic Power Control

Maxim makes no warranty, representation or guarantee regarding the suitability of its products for any particular purpose, nor does Maxim assume any lia­bility arising out of the application or use of any product or circuit and specifically disclaims any and all liability, including without limitation consequential or
incidental damages. “Typical” parameters can and do vary in different applications. All operating parameters, including “typicals” must be validated for
each customer application by customer’s technical experts. Maxim products are not designed, intended or authorized for use as components in systems
intended for surgical implant into the body, or other applications intended to support or sustain life, or for any other application in which the failure of the
Maxim product could create a situation where personal injury or death may occur.

12

____________________Maxim Integrated Products, 120 San Gabriel Drive, Sunnyvale, CA 94086 408-737-7600

© 1998 Maxim Integrated Products Printed USA is a registered trademark of Maxim Integrated Products.

Package Information

TQFPPO.EPS