______________________________________________________________________________________

15

3.0V to 5.5V, 1.25Gbps/2.5Gbps

LAN Laser Drivers

MAX3286/96

ONLY

SHDNDRV

BIASDRV

MON

LASER

Q1

POL

MD

POWER-CONTROL

AMPLIFIER

FERRITE

BEAD

B1

MONITOR

DIODE

1.7V

SMOOTH-

START

POL

MAX3286

MAX3289

MAX3296

MAX3299

Figure 12. Common Anode with Photodiode

is shown in Figure 11. The remaining discrete compo-

nents used with the common cathode without photodi-

ode configuration are as follows:

B1 = ferrite bead (see the Bias Filter section)

M1 = general-purpose PMOS device (optional)

Common Anode with Photodiode

In the common-anode configuration with photodiode, a

servo control loop is formed by an external NPN transis-

the power-control amplifier. The voltage at MD is stabi-

lized to 1.7V. The monitor photodiode current is set by

connected to the bias transistor (in this case NPN) to

obtain the desired APC loop time constant. This

improves power-supply (and ground) noise rejection. A

capacitance of 0.1µF is sufficient to obtain time con-

stants of up to 5µs in most cases. The voltage across

current.

The discrete components used with the common anode

with photodiode configuration are summarized as follows:

B1 = ferrite bead (see the Bias Filter section)

M1 = general-purpose PMOS (optional)

Programming POR Delay

A capacitor can be added to PORDLY to increase the

is within the operational range) when powering up the

part.

The delay is approximately:

See the Typical Operating Characteristics.

t

C

s

PORDLY

=

()

[]

−

14 10

6

.

100

0.1

10

1k

10k

1

10

100

Figure 11. Common Cathode without Photodiode Laser