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

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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

OPTIONAL

VCC

SHUTDOWN

CIRCUITRY

SHDNDRV

VCC

MONITOR

DIODE

SMOOTH

START

1.1V

MAX3996

MD

RSET

ID

POWER-CONTROL

AMPLIFIER

SHUTDOWN

CIRCUIT

BIAS

DISABLE

IBIAS

11Ω

LASER

L1*

BIAS

MON2

MON1

*FERRITE BEAD

Figure 11. APC Loop

monitor photodiode current is set by ID = VMD/RSET.

Determine the desired monitor current (ID), and then

select RSET = 1.1V/ID.

A bias stabilizing capacitor (CCOMP) must be connect-

ed between the COMP pin and ground to obtain the

desired APC loop time constant. This improves power-

supply and ground noise rejection. A capacitance of

0.1µF usually is sufficient to obtain time constants of up

to 35µs.

The degeneration resistance between MON2 and

ground determines the bias current that causes a fault

and affects the APC time constant. Select RMON (the

total resistance between MON2 and ground) =

400mV/(maximum bias current). A degeneration resis-

tance of 10Ω can be obtained by grounding MON1.

Increasing RMON increases the APC time constant.

The discrete components for use with the common

anode with photodiode configuration are:

CCOMP

0.1µF

COMP

RSET = 1.1V/ID

CCOMP = 0.1µF (typ)

L1 = ferrite bead, see the Bias Filter section

RMON = 400mV/(maximum bias current)

Programming POR Delay

A capacitor can be added to PORDLY to increase the

delay when powering up the part. The delay will be

approximately:

t = CPORDLY seconds

1.4 × 10−6

See the Typical Operating Characteristics section.

Designing the Laser-Compensation

Filter Network

Laser package inductance causes the laser impedance

to increase at high frequencies, leading to ringing,

overshoot, and degradation of the laser output. A laser-

compensation filter network can be used to reduce the

laser impedance at high frequencies, thereby reducing

output ringing and overshoot.

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