MAX3996 Ver la hoja de datos (PDF) - Maxim Integrated

Número de pieza

componentes Descripción

Fabricante

MAX3996

3.0V to 5.5V, 2.5Gbps VCSEL and Laser Driver

Maxim Integrated 

3.0V to 5.5V, 2.5Gbps VCSEL

and Laser Driver

3.0V TO 5.5V

ICC

VCC

VCC

MAX3996 ROUT

0.01µF

IN+

VID

RIN

0.01µF

IN-

MODULATION CURRENT

GENERATOR

ROUT

OUT-

OUT+

0.01µF

25Ω

TC

*MURATA

BLM11HA102SG

MODSET

RMOD

iOUT

FERRITE

BEAD*

iMOD

0.01µF

25Ω

Figure 1. Output Load for AC Specification

Detailed Description

The MAX3996 contains a bias generator with automatic

power control and smooth start, a laser modulator, a

power-on reset (POR) circuit, and safety circuitry

(Figure 3).

VOLTS

VIN+

VIN-

VID = VIN+ - VIN-

CURRENT

iMOD

SINGLE-ENDED SIGNAL

DIFFERENTIAL SIGNAL

100mVP-P MIN

1100mVP-P MAX

200mVP-P MIN

2200mVP-P MAX

TIME

Figure 2. Required Input Signal and Modulation-Current Polarity

Bias Generator

Figure 4 shows the bias generator circuitry that con-

tains a power-control amplifier, smooth-start circuitry,

and two bias-fault sensors. The power-control amplifier

combined with an internal NPN transistor provides DC

laser current to bias the laser in a light-emitting state.

The APC circuitry adjusts the laser bias current to main-

tain average power over temperature and changing

laser properties. The smooth-start circuitry prevents

current spikes to the laser during power-up or enable,

ensuring compliance with safety requirements and

extending the life of the laser.

VCC

FAULT SHDNDRV

PORDLY POR CIRCUIT

TX_DISABLE

SAFETY

CIRCUITRY

BIAS ENABLE

BIAS

GENERATOR

WITH SMOOTH

START

MAX3996

VCC

50Ω

50Ω

IN+

INPUT BUFFER

LASER

MODULATION

100Ω

IN-

MODULATION

ENABLE

MODULATION

FAULT

MODULATION CURRENT

GENERATOR

TC

MODSET

BIAS

MD

COMP

MON1

MON2

OUT-

OUT+

Figure 3. Laser Driver Functional Diagram

SMOOTH START

1.1V

BIAS

FAULT 1

MD

POWER-CONTROL

AMPLIFIER

MAX3996

BIAS

DISABLE

BIAS

FAULT 2

COMP

400mV

BIAS

MON2

400mV

RMON (11Ω)

MON1

Figure 4. Bias Circuitry

The MD input is connected to the anode of a monitor

diode, which is used to sense laser power. The BIAS

output is connected to the cathode of the laser through

an inductor or ferrite bead. The power-control amplifier

drives a transistor to control the laser’s bias current. In

a fault condition (Table 1), the base of the bias-driving

transistor is pulled low to ensure that bias current is

turned off.

_______________________________________________________________________________________ 7

Share Link: