Rainbow Electronics MAX3646 User Manual

General Description

The MAX3646 is a +3.3V laser driver designed for mul­tirate transceiver modules with data rates from
155Mbps to 622Mbps. Lasers can be DC-coupled to
the MAX3646 for reduced component count and ease
of multirate operation.

Laser extinction ratio control (ERC) combines the features
of automatic power control (APC), modulation compensa­tion, and built-in thermal compensation. The APC loop
maintains constant average optical power. Modulation
compensation increases the modulation current in pro­portion to the bias current. These control loops, com­bined with thermal compensation, maintain a constant
optical extinction ratio over temperature and lifetime.

The MAX3646 accepts differential data input signals.
The wide 5mA to 60mA (up to 85mA AC-coupled) mod­ulation current range and up to 100mA bias current
range, make the MAX3646 ideal for driving FP/DFB
lasers in fiber optic modules. External resistors set the
required laser current levels. The MAX3646 provides
transmit disable control (TX_DISABLE), single-point
fault tolerance, bias-current monitoring, and photocur­rent monitoring. The device also offers a latched failure
output (TX_FAULT) to indicate faults, such as when the
APC loop is no longer able to maintain the average
optical power at the required level. The MAX3646 is
compliant with the SFF-8472 transmitter diagnostic and
SFP MSA timing requirements.

The MAX3646 is offered in a 4mm x 4mm, 24-pin thin
QFN package and operates over the extended -40°C to
+85°C temperature range.

Applications

Multirate OC-3 to OC-12 FEC Transceivers
125Mbps Ethernet SFP, GBIC, and 1 x 9

Transceivers

Features

♦ Single +3.3V Power Supply

♦ 47mA Power-Supply Current

♦ 85mA Modulation Current

♦ 100mA Bias Current

♦ Automatic Power Control (APC)

♦ Modulation Compensation

♦ On-Chip Temperature Compensation

♦ Self-Biased Inputs for AC-Coupling

♦ Ground-Referenced Current Monitors

♦ Laser Shutdown and Alarm Outputs

♦ Enable Control and Laser Safety Feature

MAX3646

155Mbps to 622Mbps SFF/SFP

Laser Driver with Extinction Ratio Control

________________________________________________________________ Maxim Integrated Products 1

Ordering Information

19-3161; Rev 0; 1/04

For pricing, delivery, and ordering information, please contact Maxim/Dallas Direct! at
1-888-629-4642, or visit Maxim’s website at www.maxim-ic.com.

EVALUATION KIT

AVAILABLE

PART

TEMP

RANGE

PIN­PACKAGE

PKG
CODE

MAX3646ETG

T2444-1

BIAS

APCFILT2

V

CC

V

CC

TX_DISABLE

MODTCOMP

TH_TEMP

OUT+

APCFILT1

SHUTDOWN

GND

BC_MON

TX_FAULT

GND

V

CC

V

CC

MD

MODSET

APCSET

1

2

3

4

5

6

7891011 12

24 23 22 21 20 19

13

14

15

16

17

18

TOP VIEW

THE EXPOSED PADDLE MUST BE SOLDERED TO SUPPLY
GROUND ON THE CIRCUIT BOARD.

IN+

IN-

PC_MON

OUT-

MODBCOMP

MAX3646

Pin Configuration

Typical Application Circuit appears at end of data sheet.

-40°C to +85°C 24 Thin QFN

MAX3646

155Mbps to 622Mbps SFF/SFP
Laser Driver with Extinction Ratio Control

2 _______________________________________________________________________________________

ABSOLUTE MAXIMUM RATINGS

ELECTRICAL CHARACTERISTICS

(VCC= +2.97V to +3.63V, TA= -40°C to +85°C. Typical values are at VCC= +3.3V, I

BIAS

= 60mA, I

MOD

= 60mA, TA= +25°C, unless

otherwise noted.) (Notes 1, 2)

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.

Supply Voltage VCC...............................................-0.5V to +6.0V

IN+, IN-, TX_DISABLE, TX_FAULT, SHUTDOWN,

BC_MON, PC_MON, APCFILT1, APCFILT2,
MD, TH_TEMP, MODTCOMP, MODBCOMP,

MODSET, and APCSET Voltage.............-0.5V to (V

CC

+ 0.5V)

OUT+, OUT-, BIAS Current.............................-20mA to +150mA

Continuous Power Dissipation (T

A

= +85°C)

24-Pin QFN (derate 20.8mW/°C above +85°C) .........1805mW

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

Storage Temperature Range .............................-55°C to +150°C

PARAMETER

CONDITIONS

UNITS

POWER SUPPLY

Supply Current I

CC

(Note 3) 47 60 mA

Power-Supply Noise Rejection

f ≤ 1MHz, 100mA

P-P

(Note 4) 33 dB

I/O SPECIFICATIONS

Differential Input Swing V

ID

DC-coupled, Figure 1 0.2 2.4

V

P-P

Common-Mode Input V

CM

1.7

V

CC

­V

LASER BIAS

Bias-Current-Setting Range 1 100 mA
Bias Off Current TX_DISABLE = high 0.1 mA
Bias-Current Monitor Ratio I

BIAS

/ I

BC_MON

68 79 95

mA/mA

LASER MODULATION

Modulation Current-Setting
Range

I

MOD

(Note 5) 5 85 mA

Output Edge Speed

20% to 80%
(Notes 6, 7)

5mA ≤ I

MOD

≤ 85mA

200 ps

Output Overshoot/Undershoot

±6%

Random Jitter (Notes 6, 7) 1.1 2.5

ps

RMS

622Mbps, 5mA ≤ I

MOD

≤ 85mA 24 46

Deterministic Jitter (Notes 6, 8)

155Mbps, 5mA ≤ I

MOD

≤ 85mA 45 100

ps

P-P

5mA ≤ I

MOD

≤ 10mA

Modulation-Current Temperature
Stability

(Note 6)

10mA < I

MOD

≤ 85mA

ppm/°C

5mA ≤ I

MOD

≤ 10mA ±20

15Ω load,
T

A

= +25°C

10mA < I

MOD

≤ 85mA ±15

%

Modulation Off Current TX_DISABLE = high 0.1 mA

AUTOMATIC POWER AND EXTINCTION RATIO CONTROLS

Monitor-Diode Input Current
Range

I

MD

Average current into the MD pin 18

µA

MD Pin Voltage 1.4 V
MD Current Monitor Ratio IMD / I

PC_MON

mA/mA

SYMBOL

PSNR

MIN TYP MAX

Modulation-Current-Setting Error

(Note 7) (with 2pF between OUT+ and OUT-)

0.85 0.93 1.15

100

±175 ±600
±125 ±480

VID / 4

1500

MAX3646

155Mbps to 622Mbps SFF/SFP

Laser Driver with Extinction Ratio Control

_______________________________________________________________________________________ 3

Note 1: AC characterization is performed using the circuit in Figure 2 using a PRBS 223- 1 or equivalent pattern.
Note 2: Specifications at -40°C are guaranteed by design and characterization.
Note 3: Excluding I

BIAS

and I

MOD

. Input data is AC-coupled. TX_FAULT open, SHUTDOWN open.

Note 4: Power-supply noise rejection (PSNR) = 20log

10(Vnoise (on VCC

) / ∆V

OUT

). V

OUT

is the voltage across the 15Ω load when IN+

is high.

Note 5: The minimum required voltage at the OUT+ and OUT- pins is +0.75V.
Note 6: Guaranteed by design and characterization.
Note 7: Tested with 00001111 pattern at 622Mbps.
Note 8: DJ includes pulse-width distortion (PWD).

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

APC Loop Time Constant C

APC_FILT

= 0.01µF, ∆IMD / ∆I

BIAS

= 1/70 3.3 µs

APC Setting Stability (Note 6)

ppm/°C

APC Setting Accuracy TA = +25°C ±15 %
I

MOD

Compensation-Setting

Range by Bias

KK = ∆I

MOD

/ ∆I

BIAS

0 1.5

mA/mA

I

MOD

Compensation-Setting

Range by Temperature

TC TC = ∆I

MOD

/ ∆T (Note 6) 0 1.0

mA/°C

Threshold-Setting Range for
Temperature Compensation

T

TH

(Note 6)

°C

LASER SAFETY AND CONTROL

Bias and Modulation Turn-Off
Delay

C

APC_FILT

= 0.01µF, ∆I

MD

/ ∆I

BIAS

= 1/80

(Note 6)

5µs

Bias and Modulation Turn-On
Delay

C

APC_FILT

= 0.01µF, ∆IMD / ∆I

BIAS

= 1/80

(Note 6)

600 µs

Threshold Voltage at Monitor Pins

V

REF

Figure 5

1.3

V

INTERFACE SIGNALS

TX_DISABLE Input High V

HI

2.0 V

TX_DISABLE Input Low V

LO

R

PULL

= 45kΩ (typical) 0.8 V

VHI = V

CC

15

TX_DISABLE Input Current

V

LO

= GND -70

µA

TX_FAULT Output Low Sinking 1mA, open collector 0.4 V
Shutdown Output High Sourcing 100µA

V

Shutdown Output Low Sinking 100µA 0.4 V

ELECTRICAL CHARACTERISTICS (continued)

(VCC= +2.97V to +3.63V, TA= -40°C to +85°C. Typical values are at VCC= +3.3V, I

BIAS

= 60mA, I

MOD

= 60mA, TA= +25°C, unless

otherwise noted.) (Notes 1, 2)

±100 ±480

+10 +60

1.14

1.39

VCC - 0.4

-140

MAX3646

155Mbps to 622Mbps SFF/SFP
Laser Driver with Extinction Ratio Control

4 _______________________________________________________________________________________

Typical Operating Characteristics

(VCC= +3.3V, C

APC

= 0.01µF, I

BIAS

= 20mA, I

MOD

= 30mA, TA= +25°C, unless otherwise noted.)

OPTICAL EYE DIAGRAM

(622.08Mbps, 2

7

- 1 PRBS, 467MHz FILTER)

MAX3646 toc01

270ps/div

1310nm FP LASER

r

e

= 8.2dB

OPTICAL EYE DIAGRAM

(155Mbps, 2

7

- 1 PRBS, 117MHz FILTER)

MAX3646 toc02

1ns/div

1310nm FP LASER

r

e

= 8.2dB

ELECTRICAL EYE DIAGRAM

(I

MOD

= 30mA, 622.08MHz, 27 - 1 PRBS)

MAX3646 toc03

320ps/div

75mV/div

2pF BETWEEN OUT+

AND OUT-

SUPPLY CURRENT (ICC) vs. TEMPERATURE

(EXCLUDES BIAS AND MODULATION CURRENTS)

MAX3646 toc04

TEMPERATURE (°C)

SUPPLY CURRENT (mA)

80706050403020100-10-20-30

35

40

45

50

55

60

30

-40 90

3.63V

2.97V

3.3V

BIAS-CURRENT MONITOR RATIO

vs. TEMPERATURE

MAX3646 toc05

TEMPERATURE (°C)

I

BIAS

/I

BC_MON

(mA/mA)

807050 60-10 0 10 20 30 40-30 -20

72

74

76

78

80

82

84

86

88

90

70

-40 90

PHOTOCURRENT MONITOR RATIO

vs. TEMPERATURE

MAX3646 toc06

TEMPERATURE (°C)

I

MD

/I

PC_MON

(mA/mA)

807050 60-10 0 10 20 30 40-30 -20

0.85

0.90

0.95

1.00

1.05

1.10

1.15

1.20

0.80

-40 90

MODULATION CURRENT vs. R

MODSET

MAX3646 toc07

R

MODSET

(kΩ)

I

MOD

(mA)

10

10

20

30

40

50

60

70

80

90

0

1 100

PHOTODIODE CURRENT vs. R

APCSET

MAX3646 toc08

R

APCSET

(kΩ)

I

MD

(mA)

101

0.2

0.4

0.6

0.8

1.0

1.2

1.4

0

0.1 100

DETERMINISTIC JITTER vs.

MODULATION CURRENT

MAX3646 toc09

I

MOD

(mA)

DJ (ps

P-P

)

807050 6020 30 4010

30

40

50

60

70

80

90

100

20

090

155mbps

MAX3646

155Mbps to 622Mbps SFF/SFP

Laser Driver with Extinction Ratio Control

_______________________________________________________________________________________ 5

RANDOM JITTER vs.

MODULATION CURRENT

MAX3646 toc10

I

MOD

(mA)

RJ (ps

RMS

)

807050 6020 30 4010

0.2

0.4

0.6

0.8

1.0

1.2

1.4

1.6

1.8

2.0

0

090

COMPENSATION (K) vs. R

MODBCOMP

MAX3646 toc11

R

MODBCOMP

(kΩ)

K (mA/mA)

1010.10.01

0.1

1

10

0.01

0.001 100

TEMPERATURE COMPENSATION vs.

R

TH_TEMP

(R

MODTCOMP

= 500Ω)

MAX3646 toc12

TEMPERATURE (°C)

I

MOD

(mA)

80706050403020100

40

50

60

70

80

90

100

30

-10 90

R

TH_TEMP

= 12k

Ω

R

TH_TEMP

= 7k

Ω

R

TH_TEMP

= 4k

Ω

R

TH_TEMP

= 2k

Ω

TEMPERATURE COMPENSATION vs.

R

TH_TEMP

(R

MODTCOMP

= 10kΩ)

MAX3646 toc13

TEMPERATURE (°C)

I

MOD

(mA)

80706050403020100

32

34

36

38

40

42

44

30

-10 10090

R

TH_TEMP

= 12k

Ω

R

TH_TEMP

= 7k

Ω

R

TH_TEMP

= 4k

Ω

R

TH_TEMP

= 2k

Ω

HOT PLUG WITH TX_DISABLE LOW

MAX3646 toc14

20ms/div

V

CC

FAULT

TX_DISABLE

LASER

OUTPUT

0V

3.3V

t_init = 59.6ms

LOW

LOW

TRANSMITTER ENABLE

MAX3646 toc15

10µs/div

V

CC

FAULT

TX_DISABLE

LASER

OUTPUT

3.3V

t_on = 23.8µs

LOW

HIGH

LOW

TRANSMITTER DISABLE

MAX37646 toc16

20ns/div

V

CC

FAULT

TX_DISABLE

LASER

OUTPUT

3.3V

91.2ns

LOW

HIGH

LOW

RESPONSE TO FAULT

MAX3646 toc17

400ns/div

V

PC_MON

FAULT

TX_DISABLE

LASER

OUTPUT

t_fault = 160ns

EXTERNALLY

FORCED FAULT

FAULT RECOVERY TIME

MAX3646 toc18

40ms/div

V

PC_MON

FAULT

TX_DISABLE

LASER

OUTPUT

t_init = 58ms

EXTERNALLY
FORCED FAULT

LOW

LOWLOW

HIGH

HIGH

Typical Operating Characteristics (continued)

(VCC= +3.3V, C

APC

= 0.01µF, I

BIAS

= 20mA, I

MOD

= 30mA, TA= +25°C, unless otherwise noted.)