3.0V to 5.5V, 1.25Gbps/2.5Gbps

LAN Laser Drivers

8

_______________________________________________________________________________________

MODULATION

CONTROL

MODSET

TC

L = 3.9nH

L = 3.9nH

BIASDRV

LASER

EQUIVALENT

LOAD

(OPEN)

OUT-

OUT+

FERRITE BEAD*

*MURATA

BLM11HA102

0.01µF

0.01µF

IN+

IN-

50Ω

50Ω

25Ω

CURRENT

VOLTS

TIME

DIFFERENTIAL INPUT

RESULTING SIGNAL

MAX3286

MAX3296

Figure 1a. Output Load for AC Specification

POR

FAULT

FAULT ON MD

RESET BY EN SHUTDOWN

BY EN

SHDNDRV

OPTICAL

OUT

EN

NOTE: TIMING IS NOT TO SCALE.

Figure 1b. Fault Timing

_______________Detailed Description

The MAX3286/MAX3296 series of laser drivers contain a

bias generator with APC, laser modulator, power-on reset

(POR) circuit, and safety circuitry (Figures 2a and 2b).

Bias Generator

Figure 3 shows the bias generator circuitry containing a

power-control amplifier, controlled reference voltage,

smooth-start circuit, and window comparator. The bias

generator combined with an external PNP or NPN transis-

tor provides DC laser current to bias the laser in a light-

emitting state. When there is a monitor diode (MD) in the

laser package, the APC circuitry adjusts the laser-bias

current to maintain average power over temperature and

changing laser properties. The MD input is connected to