MAX3967 Ver la hoja de datos (PDF) - Maxim Integrated

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MAX3967

270Mbps SFP LED Driver

Maxim Integrated 

270Mbps SFP LED Driver

INPUT

BUFFER

IN+

IN-

TX_DISABLE

0

1

0

MAX3967

VCCOUT

OUT-

5Ω

COMPLEMENTARY

OUTPUT

24X

REFERENCE-VOLTAGE GENERATOR

MODULATION-

CURRENT

GENERATOR

GAIN 4X

VCC

1.2V

V

TEMP

50Ω

MAIN

OUTPUT

24X

RPREBIAS

78Ω

OUT+

35Ω

12pF

PREBIAS-CURRENT

GENERATOR

TCMIN TCNOM

TC

MODSET

RMODSET

MON

PB1

PB2

PB3

Figure 2. Functional Diagram

Modulation-Current Generator

The modulation-current generator circuit provides con-

trol of the modulation-current amplitude. This amplitude

is determined by the voltage at the MODSET pin and

external resistor RMODSET.

Do not connect bypass capacitors at the MODSET pin.

Capacitance at this pin increases high-frequency out-

put noise. The MON pin provides an optional modula-

tion-current monitor. The current sourced from the MON

pin is 1/96 of the modulation current. If used, the pin

should be connected to VEE through a resistor. The

resistance must be chosen so the voltage on MON

does not exceed 1.1V. If not used, leave MON open.

Prebias Current Generator

A prebias voltage (VPREBIAS) can be applied to the

LED to improve switching speed. The prebias current

generator creates a current that flows through the 78Ω

prebias resistor in the output stage, creating a prebias

voltage. The prebias voltage can be adjusted by selec-

tively connecting pins PB1, PB2, and PB3 to VEE. Table 1

describes the functions of PB1, PB2, and PB3.

Output Current Drivers

The modulation-current reference is switched and

amplified by the output stages.

LED package lead inductance causes ringing and

overshoot, which can be compensated with an RC filter

network. The MAX3967 includes 35Ω and 12pF of inter-

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