MAX3735ETG_技术文档

19-2529; Rev 1; 4/03

2.7Gbps, Low-Power SFP Laser Drivers

General Description

Features

ꢀ SFP Reference Design Available

The MAX3735/MAX3735A are +3.3V laser drivers for

SFP/SFF applications from 155Mbps up to 2.7Gbps.

The devices accept differential input data and provide

bias and modulation currents for driving a laser. DC-

coupling to the laser allows for multirate applications

and reduces the number of external components. The

MAX3735/MAX3735A are fully compliant with the SFP

MSA timing and the SFF-8472 transmit diagnostic

requirements.

ꢀ Fully Compliant with SFP and SFF-8472 MSAs

ꢀ Programmable Modulation Current from 10mA to

60mA (DC-Coupled)

ꢀ Programmable Modulation Current from 10mA to

85mA (AC-Coupled)

ꢀ Programmable Bias Current from 1mA to 100mA

ꢀ Edge Transition Times <51ps

An automatic power-control (APC) feedback loop is incor-

porated to maintain a constant average optical power

over temperature and lifetime. The wide modulation cur-

rent range of 10mA to 60mA (up to 85mA AC-coupled)

and bias current of 1mA to 100mA make this product

ideal for driving FP/DFB laser diodes in fiber-optic mod-

ules. The resistor range for the laser current settings is

optimized to interface with the DS1858 SFP controller IC.

ꢀ 27mA (typ) Power-Supply Current

ꢀ Multirate 155Mbps to 2.7Gbps Operation

ꢀ Automatic Average Power Control

ꢀ On-Chip Pullup Resistor for TX_DISABLE

ꢀ 24-Pin 4mm × 4mm QFN package

The MAX3735/MAX3735A provide transmit-disable con-

trol, a single-point latched transmit-failure monitor out-

put, photocurrent monitoring, and bias-current

monitoring to indicate when the APC loop is unable to

maintain the average optical power. The MAX3735A

also features improved multirate operation.

Ordering Information

PART

TEMP RANGE

-40°C to +85°C

PIN-PACKAGE

Dice*

MAX3735E/D

MAX3735ETG

MAX3735EGG

MAX3735AETG

The MAX3735/MAX3735A come in package and die

form, and operate over the extended temperature

range of -40°C to +85°C.

24 Thin QFN-EP**

24 QFN-EP**

24 Thin QFN-EP**

Applications

Gigabit Ethernet SFP/SFF Transceiver Modules

*Dice are designed to operate from -40°C to +85°C, but are

tested and guaranteed only at T = +25°C.

A

1G/2G Fibre Channel SFP/SFF Transceiver

Modules

**EP = Exposed pad.

Pin Configuration appears at end of data sheet.

Multirate OC3 to OC48-FEC SFP/SFF Transceiver

Modules

Typical Application Circuit

+3.3V

OPTIONAL SHUTDOWN

CIRCUITRY

+3.3V

0.01µF

15Ω

0.1µF

OUT-

10Ω

OUT+

IN+

SERDES

0.1µF

OUT+

MAX3735

MAX3735A

IN-

BIAS

FERRITE BEAD

MD

C

MD

DS1858/DS1859

CONTROLLER

IC

H0

H1

C

APC

R

BC_MON

PC_MON

MON1

M0N2

M0N3

+3.3V

REPRESENTS A CONTROLLED-IMPEDANCE TRANSMISSION LINE

________________________________________________________________ Maxim Integrated Products

1

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.

2.7Gbps, Low-Power SFP Laser Drivers

ABSOLUTE MAXIMUM RATINGS

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

Continuous Power Dissipation (T = +85°C )

CC

A

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

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

Voltage at IN+, IN-, TX_DISABLE, TX_FAULT,

24-Lead Thin QFN (derate 20.8mW/°C

above +85°C).............................................................1354mW

24-Lead QFN (derate 20.8mW/°C

above +85°C).............................................................1354mW

Operating Ambient Temperature Range (T )......-40°C to +85°C

SHUTDOWN...........................................-0.5V to (V

Voltage at BIAS, PC_MON, BC_MON,

+ 0.5V)

CC

A

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

Voltage at OUT+, OUT-.............................+0.5V to (V

Voltage at APCFILT1, APCFILT2..............................-0.5V to +3V

+ 0.5V)

+ 1.5V)

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

Die Attach Temperature...................................................+400°C

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

CC

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.

ELECTRICAL CHARACTERISTICS

(V

= +2.97V to +3.63V, T = -40°C to +85°C. Typical values at V

= +3.3V, I

= 20mA, I

= 30mA, T = +25°C, unless

MOD A

CC

A

CC

BIAS

otherwise noted.) (Note 1)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

50

UNITS

POWER SUPPLY

Excludes the laser bias and modulation

currents (Note 2)

Power-Supply Current

I

27

mA

CC

I/O SPECIFICATIONS

Differential Input Voltage

Common-Mode Input Voltage

Differential Input Resistance

V

= (V +) - (V -), Figure 1

200

2400

mV

P-P

ID

IN

0.6 ×V

V

CC

85

100

115

10.0

15

Ω

TX_DISABLE Input Pullup

Resistance

R

4.7

7.4

kΩ

PULL

V

= V

HIGH

LOW

CC

TX_DISABLE Input Current

µA

= GND, V

= 3.3V, R

= 7.4kΩ

PULL

-450

CC

TX_DISABLE Input High Voltage

TX_DISABLE Input Low Voltage

TX_FAULT Output High Voltage

TX_FAULT Output Low Voltage

SHUTDOWN Output High Voltage

SHUTDOWN Output Low Voltage

BIAS GENERATOR

V

2

V

IH

V

0.8

0.4

IL

V

I

= 100µA sourcing (Note 3)

= 1mA sinking (Note 3)

= 100µA sourcing

2.4

OH

OL

OH

OL

V

OL

V

- 0.4

OH

CC

1

V

= 100µA sinking

OL

Bias On-Current Range

I

Current into BIAS pin

100

mA

µA

BIAS

Current into BIAS pin during TX_FAULT or

TX_DISABLE

Bias Off-Current

Bias Overshoot

I

BIASOFF

During SFP module hot plugging

(Notes 4, 5, 11)

10

%

mA/A

%

External resistor to GND defines the voltage

gain, I

10.0

12

13

13.5

= 1mA, R

= 69.28kΩ

Bias-Current Monitor Gain

I

BIAS

BC_MON

I

= 100mA, R

= 693.25Ω

11.5

-8

13.5

+8

BIAS

BC_MON

MAX3735

Bias-Current Monitor Gain

Stability

1mA ≤ I

(Notes 4, 6)

≤ 100mA

BIAS

MAX3735A

-6

+6

2

_______________________________________________________________________________________

2.7Gbps, Low-Power SFP Laser Drivers

ELECTRICAL CHARACTERISTICS (continued)

(V

= +2.97V to +3.63V, T = -40°C to +85°C. Typical values at V

= +3.3V, I

= 20mA, I

= 30mA, T = +25°C, unless

MOD A

CC

A

CC

BIAS

otherwise noted.) (Note 1)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

MAX

UNITS

AUTOMATIC POWER-CONTROL LOOP

MD Reverse Bias Voltage

18µA ≤ I

≤ 1500µA

1.6

18

V

MD

MD Average Current Range

I

Average current into MD pin

1500

+880

µA

MD

I

= 1mA

BIAS

-880

(MAX3735)

APC closed loop

(Notes 4, 7)

Average Power-Setting Stability

ppm/°C

%

I

= 1mA

BIAS

-110

-650

-16

+110

+650

+16

(MAX3735A)

I

= 100mA

BIAS

APC Closed Loop

Average Power Setting Accuracy

MD-Current Monitor Gain

1mA ≤ I

≤ 100mA (Note 8)

BIAS

External resistor to GND

defines the voltage gain;

MAX3735

0.8

0.9

1

1.23

1.1

I

= 18µA, R

=

MD

PC_MON

I

A/A

%

PC_MON

MAX3735A

50kΩ

I

= 1.5mA, R = 600Ω

PC_MON

0.95

-10

-4

1.05

+10

+4

MD

MAX3735

18µA ≤ I

≤ 1500µA

MD

MD-Current Monitor Gain Stability

(Notes 4, 6)

MAX3735A

LASER MODULATOR

Current into OUT+ pin; R ≤ 15Ω, V

,

L

OUT+

10

60

85

V

≥ 0.6V (DC-coupled)

OUT-

Modulation On-Current Range

I

mA

MOD

Current into OUT+ pin; R ≤ 15Ω_, V

,

L

OUT+

V

≥ 2.0V (AC-coupled)

OUT-

Current into OUT+ pin during TX_FAULT or

TX_DISABLE

Modulation Off-Current

I

100

µA

ppm/°C

%

MODOFF

I

= 10mA

= 60mA

-480

-255

+480

+255

MOD

Modulation-Current Stability

(Note 4)

MOD

Modulation-Current Absolute

Accuracy

10mA ≤ I

≤ 60mA (Note 8)

-15

+15

MOD

Modulation-Current Rise Time

Modulation-Current Fall Time

t

20% to 80%, 10mA ≤ I

≤ 60mA (Note 4)

42

50

65

80

ps

R

MOD

t

F

MOD

10mA ≤ I

(Notes 4, 9, 10)

≤ 60mA at 2.67Gbps

MOD

18

38

Deterministic Jitter

Random Jitter

At 1.25Gbps (K28.5 pattern)

At 622Mbps (Note 9)

At 155Mbps (Note 9)

11.5

18

ps

40

RJ

10mA ≤ I

≤ 60mA (Note 4)

0.7

1.0

ps

RMS

MOD

_______________________________________________________________________________________

3

2.7Gbps, Low-Power SFP Laser Drivers

ELECTRICAL CHARACTERISTICS (continued)

(V

= +2.97V to +3.63V, T = -40°C to +85°C. Typical values at V

= +3.3V, I

= 20mA, I

= 30mA, T = +25°C, unless

MOD A

CC

A

CC

BIAS

otherwise noted.) (Note 1)

PARAMETER

SYMBOL

CONDITIONS

MIN

TYP

1.30

MAX

1.39

UNITS

SAFETY FEATURES

TX_FAULT always occurs for V

1.38V, TX_FAULT never occurs for

≤ 1.22V

≥

BC_MON

Excessive Bias-Current

Comparator Threshold Range

1.22

V

BC_MON

TX_FAULT always occurs for V

1.38V, TX_FAULT never occurs for

≤ 1.22V

PC_MON

Excessive MD-Current

Comparator Threshold Range

1.22

V

PC_MON

SFP TIMING REQUIREMENTS

Time from rising edge of TX_DISABLE to

TX_DISABLE Assert Time

t_off

t_on

I

= I

and I

= I

MODOFF

0.14

5

µs

BIAS

BIASOFF

MOD

(Note 4)

Time from falling edge

of TX_DISABLE to

C

= 2.7nF,

APC

1

ms

µs

MAX3735 (Note 4)

I

and I

at 95%

BIAS

MOD

TX_DISABLE Negate Time

of steady state when

TX_FAULT = 0 before

reset

MAX3735A

(Note 11)

600

Time from falling edge of TX_DISABLE to

and I at 95% of steady state when

TX_FAULT = 1 before reset (Note 4)

TX_DISABLE Negate Time

During FAULT Recovery

I

t_onFAULT

60

200

ms

BIAS

MOD

TX_FAULT Reset Time or Power-

On Time

From power-on or negation of TX_FAULT

using TX_DISABLE (Note 4)

t_init

60

200

50

5

ms

µs

Time from fault to TX_FAULT on, C

≤

FAULT

TX_FAULT Assert Time

TX_DISABLE to Reset

t_fault

3.3

20pF, R

= 4.7kΩ (Note 4)

FAULT

Time TX_DISABLE must be held high to

reset TX_FAULT (Note 4)

Note 1: Specifications at -40°C are guaranteed by design and characterization. Dice are tested at T = +25°C only.

A

Note 2: Maximum value is specified at I

= 60mA, I

= 100mA.

MOD

BIAS

Note 3: TX_FAULT is an open-collector output and must be pulled up with a 4.7kΩ to 10kΩ resistor.

Note 4: Guaranteed by design and characterization.

Note 5:

V

CC

turn-on time must be ≤ 0.8s, DC-coupled interface.

Note 6: Gain stability is defined by the digital diagnostic document (SFF-8472, rev. 9.0) over temperature and supply variation.

Note 7: Assuming that the laser diode to photodiode transfer function does not change with temperature.

Note 8: Accuracy refers to part-to-part variation.

23

Note 9: Deterministic jitter is measured using a 2 - 1 PRBS or equivalent pattern.

Note 10: Broadband noise is filtered through the network as shown in Figure 3. One capacitor,

C < 0.47µF, and one 0603 ferrite bead or inductor can be added (optional). This supply voltage filtering reduces the hot-

plugging inrush current. The supply noise must be < 100mV

up to 2MHz.

P-P

Note 11: C

values chosen as shown in Table 4 (MAX3735A).

APC

4

_______________________________________________________________________________________

2.7Gbps, Low-Power SFP Laser Drivers

V

CC

VOLTAGE

V

+

OUT

30Ω

(100mV min,

1200mV max)

V

-

OUT

MAX3735

MAX3735A

OUT-

(V +) - (V -)

IN

(200mV min,

P-P

30Ω

75Ω

2400mV max)

P-P

0.5pF

OUT+

I

+

CURRENT

OUT

OSCILLOSCOPE

I +

OUT

I

MOD

50Ω

TIME

Figure 1. Required Input Signal and Output Polarity

Figure 2. Output Termination for Characterization

HOST BOARD

MODULE

FILTER DEFINED BY SFP MSA

TO LASER

L1

1µH

SOURCE

NOISE

DRIVER V

CC

OPTIONAL

VOLTAGE

SUPPLY

C1

0.1µF

C2

10µF

C3

0.1µF

Figure 3. Supply Filter

_______________________________________________________________________________________

5

2.7Gbps, Low-Power SFP Laser Drivers

Typical Operating Characteristics

(V

= +3.3V, C

= 0.01µF, I

= 20mA, and I

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

CC

APC

BIAS

MOD A

OPTICAL EYE

MAX3735 toc01

MAX3735 toc02

E

= 8.2dB, 2.7Gbps, 2.3GHz FILTER

E

= 8.2dB, 1.25Gbps, 900MHz FILTER

R

7

2 - 1 PRBS, 1310nm FP LASER

K28.5 PATTERN, 1310nm FP LASER

54ps/div

115ps/div

OPTICAL EYE

ELECTRICAL EYE

MAX3735 toc03

MAX3735 toc04

7

2.7Gbps, 2 - 1 PRBS,

E

= 12dB, 155Mbps, 117MHz FILTER

R

7

30mA MODULATION

2 - 1 PRBS, 1310nm FP LASER

85mV/div

919ps/div

58ps/div

BIAS-CURRENT MONITOR GAIN

vs. TEMPERATURE

SUPPLY CURRENT vs. TEMPERATURE

20

18

16

14

12

10

EXCLUDES I

BIAS

AND I

MOD

70

55

40

25

10

-40

-15

10

35

60

85

-40

-15

10

35

60

85

TEMPERATURE (°C)

6

_______________________________________________________________________________________

2.7Gbps, Low-Power SFP Laser Drivers

Typical Operating Characteristics (continued)

(V

= +3.3V, C

= 0.01µF, I

= 20mA, and I

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

CC

APC

BIAS

MOD A

PHOTOCURRENT MONITOR GAIN

vs. TEMPERATURE

MODULATION CURRENT vs. R

MONITOR DIODE CURRENT vs. R

MODSET

APCSET

3.0

100

90

80

70

60

50

40

30

20

10

0

1.8

1.6

1.4

1.2

1.0

0.8

0.6

0.4

0.2

0

2.5

2.0

1.5

1.0

0.5

0

-40

-15

10

35

60

85

1

10

100

0

1

10

100

TEMPERATURE (°C)

R

(kΩ)

R

(kΩ)

MODSET

APCSET

DETERMINISTIC JITTER

vs. MODULATION CURRENT

RANDOM JITTER

vs. MODULATION CURRENT

EDGE TRANSITION TIME

vs. MODULATION CURRENT

60

50

40

30

20

3.0

2.5

2.0

1.5

1.0

0.5

0

80

70

60

50

40

30

20

FALL TIME

RISE TIME

DJ (INCLUDING PWD)

PWD

10

0

10

20

30

40

(mA)

50

60

10

20

30

40

(mA)

50

60

10

20

30

40

(mA)

50

60

I

MOD

I

MOD

HOT PLUG WITH TX_DISABLE LOW

STARTUP WITH SLOW RAMPING SUPPLY

TRANSMITTER ENABLE

MAX3735 toc15

MAX3735 toc13

MAX3735 toc14

3.3V

LOW

3.3V

V

CC

0V

V

0V

CC

V

CC

FAULT

LOW

FAULT

TX_DISABLE HIGH

t_on = 44µs

12µs/div

LOW

TX_DISABLE

t_init = 60ms

20ms/div

LASER

OUTPUT

LASER

OUTPUT

LASER

OUTPUT

20ms/div

_______________________________________________________________________________________

7

2.7Gbps, Low-Power SFP Laser Drivers

Typical Operating Characteristics (continued)

(V

= +3.3V, C

= 0.01µF, I

= 20mA, and I

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

CC

APC

BIAS

MOD A

RESPONSE TO FAULT

TRANSMITTER DISABLE

MAX3735 toc17

MAX3735 toc16

EXTERNALLY

FORCED FAULT

3.3V

V

CC

V

PC_MON

t_fault = 0.9µs

HIGH

LOW

FAULT

LOW

FAULT

TX_DISABLE

LOW

TX_DISABLE

HIGH

t_off = 134ns

LASER

OUTPUT

LASER

OUTPUT

1µs/div

40ns/div

FAULT RECOVERY TIME

FREQUENT ASSERTION OF TX_DISABLE

MAX3735 toc18

MAX3735 toc19

V

PC_MON

EXTERNAL

FAULT REMOVED

EXTERNALLY

FORCED FAULT

HIGH

FAULT

LOW

TX_DISABLE

HIGH

TX_DISABLE

LOW

t_init = 60ms

LASER

OUTPUT

LASER

OUTPUT

100ms/div

4µs/div

8

_______________________________________________________________________________________

2.7Gbps, Low-Power SFP Laser Drivers

Pin Description

NAME

FUNCTION

1, 4, 8, 14, 18

V

+3.3V Supply Voltage

Noninverted Data Input

Inverted Data Input

CC

2

3

IN+

IN-

Photodiode Current Monitor Output. Current out of this pin develops a ground-referenced voltage

across an external resistor that is proportional to the monitor diode current.

5

PC_MON

Bias Current Monitor Output. Current out of this pin develops a ground-referenced voltage across an

external resistor that is proportional to the bias current.

6

7, 12, 22

9

BC_MON

GND

Ground

Shutdown Driver Output. Voltage output to control an external transistor for optional shutdown

circuitry.

SHUTDOWN

10

11

13

TX_FAULT Open-Collector Transmit Fault Indicator (Table 1).

MODSET

BIAS

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

Laser Bias Current Output

Noninverted Modulation Current Output. Connect pins 15 and 16 externally to minimize parasitic

15, 16

17

OUT+

OUT-

MD

inductance of the package. I

flows into this pin when input data is high.

MOD

Inverted Modulation Current Output. I

flows into this pin when input data is low.

MOD

Monitor Diode Input. Connect this pin to the anode of a monitor photodiode. A capacitor to ground is

required to filter the high-speed AC monitor photocurrent.

19

Connect a capacitor (C

pole of the APC feedback loop.

) between pin 20 (APCFILT1) and pin 21 (APCFILT2) to set the dominant

APC

20

APCFILT1

21

23

APCFILT2

APCSET

See APCFILT1

A resistor connected from this pin to ground sets the desired average optical power.

Transmitter Disable, TTL. Laser output is disabled when TX_DISABLE is asserted high or left

unconnected. The laser output is enabled when this pin is asserted low.

24

EP

TX_DISABLE

Exposed

Pad

Ground. Must be soldered to the circuit board ground for proper thermal and electrical performance

(see the Exposed Pad Package section).

To interface with the laser diode, a damping resistor

Detailed Description

(R ) is required for impedance matching. The com-

D

The MAX3735/MAX3735A laser drivers consist of three

parts: a high-speed modulation driver, a laser-biasing

block with automatic power control (APC), and safety

circuitry (Figure 4). The circuit design is optimized for

high-speed and low-voltage (+3.3V) operation.

bined resistance of the series damping resistor and the

equivalent series resistance of the laser diode should

equal 15Ω. To reduce optical output aberrations and

duty-cycle distortion caused by laser diode parasitic

inductance, an RC shunt network might be necessary.

Refer to Maxim Application Note HFAN 02.0: Interfacing

Maxim’s Laser Drivers to Laser Diodes for more informa-

tion.

High-Speed Modulation Driver

The output stage are composed of a high-speed differ-

ential pair and a programmable modulation current

source. The MAX3735/MAX3735A are optimized for dri-

ving a 15Ω load; the minimum instantaneous voltage

required at OUT+ is 0.6V. Modulation current swings up

to 60mA are possible when the laser diode is DC-cou-

pled to the driver and up to 85mA when the laser diode

is AC-coupled to the driver.

At data rates of 2.7Gbps, any capacitive load at the

cathode of a laser diode degrades optical output perfor-

mance. Because the BIAS output is directly connected

to the laser cathode, minimize the parasitic capacitance

associated with the pin by using an inductor to isolate

the BIAS pin parasitics from the laser cathode.

_______________________________________________________________________________________

9

2.7Gbps, Low-Power SFP Laser Drivers

V

CC

SHUTDOWN

V

CC

MAX3735

MAX3735A

INPUT BUFFER

15Ω

OUT-

IN+

IN-

DATA

PATH

100Ω

R

D

OUT+

BIAS

I

MOD

V

CC

V

CC

I

MD

1

I

BIAS

V

CC

PC_MON

I

BIAS

MOD

ENABLE

V

BG

APCSET

MD

ENABLE

x38

I

R

APCSET

R

PC_MON

V

CC

X270

SAFETY LOGIC

AND

I

BIAS

76

I

MD

C

MD

POWER

DETECTOR

V

BG

V

CC

BC_MON

x1

(4.7kΩ

TO 10kΩ)

R

BC_MON

MODSET

APCFILT1

APCFILT2

R

MODSET

TX_FAULT

TX_DISABLE

SHUTDOWN

C

APC

Figure 4. Functional Diagram

response to various single-point failures. The transmit

fault condition is latched until reset by a toggle of

Laser-Biasing and APC

To maintain constant average optical power, the

MAX3735/MAX3735A incorporate an APC loop to com-

pensate for the changes in laser threshold current over

temperature and lifetime. A back-facet photodiode

mounted in the laser package is used to convert the

optical power into a photocurrent. The APC loop

adjusts the laser bias current so that the monitor cur-

TX_DISABLE or V . The laser driver offers redundant

CC

laser diode shutdown through the optional shutdown

circuitry (see the Typical Applications Circuit). The

TX_FAULT pin should be pulled high with a 4.7kΩ to

10kΩ resistor to V

as required by the SFP MSA.

CC

Safety Circuitry Current Monitors

The MAX3735/MAX3735A feature monitors (BC_MON,

rent is matched to a reference current set by R

.

APCSET

The time constant of the APC loop is determined by an

external capacitor (C ). For possible C values,

PC_MON) for bias current (I

MD

) and photo current

BIAS

APC

(I ). The monitors are realized by mirroring a fraction

see the Applications Information section.

of the currents and developing voltages across external

resistors connected to ground. Voltages greater than

1.38V at PC_MON or BC_MON result in a fault state.

For example, connecting a 100Ω resistor to ground on

each monitor output gives the following relationships:

Safety Circuitry

The safety circuitry contains an input disable

(TX_DISABLE), a latched fault output (TX_FAULT), and

fault detectors (Figure 5). This circuitry monitors the

operation of the laser driver and forces a shutdown if a

fault is detected (Table 1). A single-point fault can be a

V

= (I

/ 76) x 100Ω

x 100Ω

BC_MON

PC_MON

BIAS

= I

MD

short to V

or GND. See Table 2 to view the circuit

CC

10 ______________________________________________________________________________________

2.7Gbps, Low-Power SFP Laser Drivers

V

CC

POR AND COUNTER

FOR t_init

MAX3735

MAX3735A

I

MOD

ENABLE

TX_DISABLE

I

BIAS

ENABLE

100ns DELAY

COUNTER FOR

t_onfault

V

CC

R

S

Q

I

MD

1

V

BG

PC_MON

RS

LATCH

COMP

R

PC_MON

SHUTDOWN

TX_FAULT

BG

CMOS

I

BIAS

76

BC_MON

MODSET

SHORT-

CIRCUIT

TTL

BC_MON

OPEN COLLECTOR

DETECTOR

Figure 5. Safety Circuitry

section, and select the value of R

that corre-

MODSET

Table 1. Typical Fault Conditions

sponds to the required current at +25°C.

If any of the I/O pins is shorted to GND or V (single-

CC

point failure, see Table 2), and the bias current or the

photocurrent exceed the programmed threshold.

Programming the APC Loop

1.

Program the average optical power by adjusting -R

SET

APC-

. To select the resistance, determine the desired moni-

tor current to be maintained over temperature and

lifetime. See the Monitor Diode Current vs. R

End-of-life (EOL) condition of the laser diode. The bias

current and/or the photocurrent exceed the

programmed threshold.

APCSET

2.

3.

4.

graph in the Typical Operating Characteristics section,

and select the value of R

required current.

that corresponds to the

APCSET

Laser cathode is grounded and the photocurrent

exceeds the programmed thresholds.

Interfacing with Laser Diodes

To minimize optical output aberrations caused by sig-

nal reflections at the electrical interface to the laser

No feedback for the APC loop (broken interconnection,

defective monitor photodiode), and the bias current

exceeds the programmed threshold.

diode, a series-damping resistor (R ) is required

D

(Figure 4). Additionally, the MAX3735/MAX3735A out-

Design Procedure

puts are optimized for a 15Ω load. Therefore, the series

combination of R and R , where R represents the

D

L

When designing a laser transmitter, the optical output

usually is expressed in terms of average power and

extinction ratio. Table 3 shows relationships helpful in

converting between the optical average power and the

modulation current. These relationships are valid if the

mark density and duty cycle of the optical waveform

are 50%.

laser-diode resistance, should equal 15Ω. Typical val-

ues for R are 8Ω to 13Ω. For best performance, place

D

a bypass capacitor (0.01µF typ) as close as possible to

the anode of the laser diode. An RC shunt network

between the laser cathode and ground minimizes opti-

cal output aberrations. Starting values for most coaxial

lasers are R

= 50Ω in series with C

= 8pF.

COMP

Programming the Modulation Current

Adjust these values experimentally until the optical out-

put waveform is optimized. Refer to Maxim Application

Note: HFAN 02.0: Interfacing Maxim’s Laser Drivers to

Laser Diodes for more information.

For a given laser power (P

), slope efficiency (η), and

AVG

extinction ratio (r ), the modulation current can be calcu-

e

lated using Table 3. See the Modulation Current vs.

R

graph in the Typical Operating Characteristics

MODSET

______________________________________________________________________________________ 11

2.7Gbps, Low-Power SFP Laser Drivers

Table 2. Circuit Responses to Various Single-Point Faults

CIRCUIT RESPONSE TO OVERVOLTAGE

OR SHORT TO V

CIRCUIT RESPONSE TO UNDERVOLTAGE

OR SHORT TO GROUND

PIN NAME

CC

TX_FAULT

Does not affect laser power.

Normal condition for circuit operation.

The optical average power increases and a fault occurs The optical average power decreases and the APC

if V exceeds the threshold. The APC loop loop responds by increasing the bias current. A fault

state occurs if V exceeds the threshold voltage.

TX_DISABLE

Modulation and bias currents are disabled.

IN+

IN-

PC_MON

responds by decreasing the bias current.

BC_MON

The optical average power decreases and the APC

loop responds by increasing the bias current. A fault

The optical average power increases and a fault occurs

if V exceeds the threshold. The APC loop

PC_MON

state occurs if V

exceeds the threshold voltage. responds by decreasing the bias current.

BC_MON

The APC circuit responds by increasing bias current

MD

SHUTDOWN

BIAS

Disables bias current. A fault state occurs.

until a fault is detected, then a fault state* occurs.

Does not affect laser power.

Does not affect laser power. If the shutdown circuitry is

used, laser current is disabled and a fault state* occurs.

In this condition, laser forward voltage is 0V and no light Fault state* occurs. If the shutdown circuitry is used, the

is emitted. laser current is disabled.

The APC circuit responds by increasing the bias current Fault state* occurs. If the shutdown circuitry is used,

OUT+

until a fault is detected, then a fault state* occurs.

laser current is disabled.

OUT-

Does not affect laser power.

Fault state* occurs.

Does not affect laser power.

PC_MON

BC_MON

Fault state* occurs.

IBIAS increases until V

voltage.

exceeds the threshold

IBIAS increases until V

voltage.

exceeds the threshold

BC_MON

APCFILT1

APCFILT2

IBIAS increases until V

voltage.

IBIAS increases until V

voltage.

BC_MON

MODSET

APCSET

Does not affect laser power.

Fault state* occurs.

*A fault state asserts the TX_FAULT pin, disables the modulation and bias currents, and asserts the SHUTDOWN pin.

Pattern-Dependent Jitter

Table 3. Optical Power Definitions

To minimize the pattern-dependent jitter associated

with the APC loop time constant, and to guarantee loop

stability, connect a capacitor between APCFILT1 and

APCFILT2 (see the Applications Information section for

PARAMETER

Average Power

SYMBOL

RELATION

= (P + P ) / 2

P

AVG

0

1

more information about choosing C

values). A

Extinction Ratio

r

r = P / P

APC

e

1

0

AVG

capacitor attached to the photodiode anode (C ) is

MD

Optical Power High

Optical Power Low

Optical Amplitude

P

P = 2P

1

x r / (r + 1)

e e

1

0

also recommended to filter transient currents that origi-

nate from the photodiode. To maintain stability and

proper phase margin associated with the two poles

P = 2P

0

/ (r + 1)

e

P

= P - P

P-P 1 0

P-P

created by C

and C

, C

should be 20x

APC

MD

Laser Slope

Efficiency

η

η = P

/ I

P-P MOD

greater than C

for the MAX3735. C

should be 4x

MD

APC

to 20x greater than C

for the MAX3735A.

MD

Modulation Current

I

= P

/ η

P-P

MOD

12 ______________________________________________________________________________________

2.7Gbps, Low-Power SFP Laser Drivers

Input Termination Requirements

The MAX3735/MAX3735A data inputs are SFP MSA

compliant. On-chip 100Ω differential input impedance is

provided for optimal termination (Figure 6). Because of

the on-chip biasing network, the MAX3735/MAX3735A

inputs self-bias to the proper operating point to accom-

modate AC-coupling.

Determine R

APCSET

The desired monitor diode current is estimated by I

MD

= P

SET

x ρ

= 200µA. The Monitor Diode vs. R

AVG

MON APC-

graph in the Typical Operating Characteristics sec-

should be 3kΩ. The value can

tion shows that R

APCSET

also be estimated using the equation below:

I

= 1.23 / (2 × R )

APCSET

MD

Optional Shutdown Output Circuitry

The SHUTDOWN control output features extended eye

safety when the laser cathode is grounded. An external

transistor is required to implement this circuit (Figure 4).

In the event of a fault, SHUTDOWN asserts high, plac-

ing the optional shutdown transistor in cutoff mode and

thereby shutting off the laser current.

Determine R

MODSET

To achieve a minimum extinction ratio (r ) of 6.6 over

e

temperature and lifetime, calculate the required extinc-

tion ratio at +25°C. Assuming the results of the calcula-

tion are r = 20 at +25°C, the peak-to-peak optical

e

P-P

power P

= 1.81mW, according to Table 3. The

required modulation current is 1.81mW / (0.05mW/mA)

= 36.2mA. The Modulation Current vs. R graph

MODSET

Applications Information

An example of how to set up the MAX3735/MAX3735A

follows:

in the Typical Operating Characteristics section shows

that R should be 9.5kΩ. The value can also be

estimated using the equation below:

MODSET

Select a communications-grade laser for 2.488Gbps.

I

= 1.23 / (0.0037 × R

)

MODSET

MOD

Assume that the laser output average power is P

=

AVG

Determine C

APC

0dBm, the operating temperature is -40°C to +85°C,

minimum extinction ratio is 6.6 (8.2dB), and the laser

diode has the following characteristics:

In order to meet SFP timing requirements and minimize

pattern-dependent jitter, the CAPC capacitor value is

determined by the laser-to-monitor transfer and other

variables. The following equations and table can be

used to choose the CAPC values for the MAX3735 and

MAX3735A, respectively. The equations and table

assume a DC-coupled laser. Refer to Maxim

Application Note HFDN 23.0: Choosing the APC Loop

Wavelength: λ = 1.3µm

Threshold current: I = 22mA at +25°C

TH

Threshold temperature coefficient: β = 1.3% / °C

TH

Laser-to-monitor transfer: ρ

= 0.2A/W

MON

Laser slope efficiency: η = 0.05mW/mA at +25°C

V

CC

V

CC

MAX3735

MAX3735A

16kΩ

PACKAGE

0.81nH

0.11pF

MAX3735

MAX3735A

V

CC

OUT-

OUT+

PACKAGE

0.97nH

IN+

0.11pF

50Ω

0.99nH

0.11pF

V

CC

0.97nH

IN-

OUT+

0.99nH

0.11pF

24kΩ

K = 0.3

Figure 6. Simplified Input Structure

Figure 7. Simplified Output Structure

______________________________________________________________________________________ 13

2.7Gbps, Low-Power SFP Laser Drivers

Capacitors Used with MAX3735/MAX3735A SFP Module

isolates laser forward voltage from the output circuitry

Designs for more information on choosing C

for DC-

and allows the output at OUT+ to swing above and

APC

and AC-coupled laser interfaces.

below the supply voltage (V ). When AC-coupled, the

CC

MAX3735/MAX3735A modulation current can be pro-

grammed from 10mA to 85mA. Refer to Maxim

Application Note HFAN 02.0: Interfacing Maxim’s Laser

Drivers to Laser Diodes for more information on AC-

coupling laser drivers to laser diodes.

MAX3735

Use the following equation to find the C

using the MAX3735:

value when

APC

C

APC

= 4.04 × 10^-9× t

× η × ρ

(29.3 + 20.6 I

-

_on

MON

- 7.78 I

TH

0.22 I ²) × (1947 + 833 I

²+ 0.103

MOD

TH

MOD

Interface Models

Figures 6 and 7 show simplified input and output cir-

cuits for the MAX3735/MAX3735A laser driver. If dice

are used, replace package parasitic elements with

bondwire parasitic elements.

3

I

)

MOD

where units are:

C

APC

in µF, I , and I

in mA and t

in µs. C

MD

can

APC

TH

MOD

ON

then be chosen as approximately 20x smaller than C

for the MAX3735.

Wire Bonding Die

The MAX3735 uses gold metalization with a thickness of

5µm (typ). Maxim characterized this circuit with gold wire

ball bonding (1-mil diameter wire). Die-pad size is 94 mil

(2388µm) square, and die thickness is 15 mil (381µm).

Refer to Maxim Application Note HFAN-08.0.1:

Understanding Bonding Coordinates and Physical Die

Size for additional information.

MAX3735A

when using the MAX3735A.

Use Table 4 to choose C

APC

C

should be chosen according to the highest gain of

the lasers (generally at cold temperature). C

selec-

APC

tion assumes a 34% reduction in the gain of the lasers at

+85°C from the cold (-40°C) values.

Table 4. MAX3735A CAPC Selection

Layout Considerations

To minimize inductance, keep the connections between

the MAX3735 output pins and laser diode 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 tech-

niques and multiple-layer boards with uninterrupted

ground planes to minimize EMI and crosstalk.

LASER GAIN (A/A)

C

(µF)

APC

0.005

0.007

0.010

0.020

0.030

0.040

0.039

0.047

0.068

0.100

0.120

Exposed-Pad Package

The exposed pad on the 24-pin QFN provides a very

low thermal resistance path for heat removal from the IC.

The pad is also electrical ground on the MAX3735/

MAX3735A and must be soldered to the circuit board

ground for proper thermal and electrical performance.

Refer to Maxim Application Note HFAN-08.1: Thermal

Considerations for QFN and Other Exposed-Pad

Packages for additional information.

where Gain = I /(I

- I + 0.5 x I

) for DC-cou-

MD BIAS TH

MOD

pled lasers. C

can then be chosen as approximately

MD

4x to 20x smaller than C

for the MAX3735A

APC

Using the MAX3735/MAX3735A

with Digital Potentiometers

For more information on using the MAX3735/MAX3735A

with the Dallas DS1858/DS1859 SFP controller, refer to

Maxim Application Note HFAN 2.3.3: Optimizing the

Resolution of Laser Driver Setting Using Linear Digital

Potentiometers for more information.

Laser Safety and IEC 825

Using the MAX3735/MAX3735A laser driver alone does

not ensure that a transmitter design is compliant with IEC

825. The entire transmitter circuit and component selec-

tions must be considered. Each user must determine the

level of fault tolerance required by the application, recog-

nizing that Maxim products are neither designed nor

authorized for use as components in systems intended

for surgical implant into the body, for applications intend-

ed to support or sustain life, or for any other application

in which the failure of a Maxim product could create a

situation where personal injury or death may occur.

Modulation Currents Exceeding 60mA

For applications requiring a modulation current greater

than 60mA, headroom is insufficient for proper opera-

tion of the laser driver if the laser is DC-coupled. To

avoid this problem, the MAX3735/MAX3735A’s modula-

tion output can be AC-coupled to the cathode of a laser

diode. An external pullup inductor is necessary to DC-

bias the modulation output at V . Such a configuration

CC

14 ______________________________________________________________________________________

2.7Gbps, Low-Power SFP Laser Drivers

MAX3735 Chip Topography

0.079"

(2.007mm)

GND

7

TX_DISABLE APCSET

GND

10

APCFILT2 APCFILT1

MD

13

GND

14

8

9

11

12

V

6

5

4

3

CC

15

16

17

V

CC

OUT-

0.060"

(1.524mm)

OUT+

IN+

IN-

18

19

20

V

CC

OUT+

V

CC

PC_MON

BC_MON

2

1

21

BIAS

29

28

27

26

25

24

23

22

INDEX

PAD

GND

V

CC

SHUTDOWN TX_FAULT MODSET

GND

______________________________________________________________________________________ 15

2.7Gbps, Low-Power SFP Laser Drivers

Bonding Coordinates

Pin Configuration

Table 5. MAX3735 Bondpad Locations

TOP VIEW

COORDINATES

PAD

NAME

X

Y

1*

2

BC_MON

PC_MON

47

24

23

22

21

20

19

47

229

514

696

878

1063

1149

1032

888

742

579

433

289

93

V

1

2

3

4

5

6

18

17

16

15

14

13

V

CC

3

V

47

CC

IN+

IN-

OUT-

OUT+

4

IN-

47

5

IN+

47

MAX3735

MAX3735A

6

V

47

CC

V

CC

7

GND

TX_DISABLE

APCSET

GND

242

452

636

819

1008

1193

1383

1567

1758

1578

1401

1205

1016

818

623

435

245

PC_MON

BC_MON

V

CC

8

9

BIAS

10

11

12

13

14

15

16**

17**

18**

19**

20

21

22

23

24

25

26

27

28

29

7

8

9

10

11

12

APCFILT2

APCFILT1

MD

GND

Thin QFN*

(4mm x 4mm)

V

CC

OUT-

OUT+

*THE EXPOSED PAD MUST BE CONNECTED TO CIRCUIT BOARD GROUND FOR PROPER

THERMAL AND ELECTRICAL PERFORMANCE.

Chip Information

TRANSISTOR COUNT: 327

V

CC

BIAS

GND

SUBSTRATE CONNECTED TO GND

DIE SIZE: 60 mils x 79 mils

-64

GND

-64

PROCESS: SiGe Bipolar

MODSET

TX_FAULT

SHUTDOWN

-64

V

-64

CC

GND

-64

*Index pad. Orient the die with this pad in the lower-left corner.

**Bond out both pairs of OUT- and OUT+ to minimize series

inductance.

16 ______________________________________________________________________________________

2.7Gbps, Low-Power SFP Laser Drivers

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

PACKAGE OUTLINE

12,16,20,24L QFN, 4x4x0.90 MM

1

21-0106

E

2

PACKAGE OUTLINE

12,16,20,24L QFN, 4x4x0.90 MM

2

21-0106

E

2

______________________________________________________________________________________ 17

2.7Gbps, Low-Power SFP Laser Drivers

Package Information

(The package drawing(s) in this data sheet may not reflect the most current specifications. For the latest package outline information,

go to www.maxim-ic.com/packages.)

PACKAGE OUTLINE

12,16,20,24L QFN THIN, 4x4x0.8 mm

21-0139

A

PACKAGE OUTLINE

12,16,20,24L QFN THIN, 4x4x0.8 mm

21-0139

A

Maxim cannot assume responsibility for use of any circuitry other than circuitry entirely embodied in a Maxim product. No circuit patent licenses are

implied. Maxim reserves the right to change the circuitry and specifications without notice at any time.

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

Printed USA

is a registered trademark of Maxim Integrated Products.


型号：	MAX3735ETG
厂家：	MAXIM INTEGRATED PRODUCTS
描述：	2.7Gbps, Low-Power SFP Laser Drivers 2.7Gbps，低功耗SFP激光驱动器驱动器
文件：	总18页 (文件大小：1732K)
中文：	中文翻译
下载：	下载PDF数据表文档文件

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