MAX3263 데이터 시트보기 (PDF) - Maxim Integrated

부품명

상세내역

제조사

MAX3263

Single +5V, Fully Integrated, 155Mbps Laser Diode Driver

Maxim Integrated 

Single +5V, Fully Integrated,

155Mbps Laser Diode Driver

18Ω

+5V

OUT+

MAX3263

IPIN

IBIASOUT

OUT-

≥0.1µF

10µH

FERRITE

BEAD

0.01µF

AS CLOSE TO THE

LASER

LASER ANODE AS

POSSIBLE

PHOTO-

DIODE

25Ω

C

SHUNT RC

AS CLOSE TO THE

18Ω

LASER CATHODE AS

POSSIBLE

Figure 5. Typical Laser Interface with Bias Compensation

heat. Fortunately, a substantial portion of this power is

dissipated across the laser diode. A typical laser diode

drops approximately 1.6V when forward biased. This

leaves 3.4V at the MAX3263’s OUT- terminal. It is safe to

reduce the output terminal voltage even further with a

series damping resistor. Terminal voltage levels down to

2.2V can be used without degrading the laser driver’s

high-frequency performance. Power dissipation can be

further reduced by adding a series resistor on the laser

driver’s OUT+ side. Select the series resistor so the

OUT+ terminal voltage does not drop below 2.2V with the

maximum modulation current.

_____________Applications Information

Programming the MAX3263 Laser Driver

Programming the MAX3263 is best explained by an

example. Assume the following laser diode characteris-

tics:

Wavelength

λ

1300nm

Threshold Current ITH 20mA at +25°C(+0.35mA/

°C temperature variation)

Monitor Responsivity ρmon 0.1A/W (monitor current /

average optical power

into the fiber)

Modulation Efficiency η

0.1mW/mA (worst case)

Now assume the communications system has the fol-

lowing requirements:

Average Power

PAVE

0dBm (1mW)

Extinction Ratio

Er

6dB (Er = 4)

Temperature Range Tr

0°C to +70°C

1) Determine the value of IPINSET:

The desired monitor-diode current is (PAVE)(ρmon) =

(1mW)(0.1A/W) = 100µA. The RPINSET vs. Monitor

Current graph in the Typical Operating Characteristics

show that RPINSET should be 18kΩ.

2) Determine RMODSET:

The average power is defined as (P1 + P0) / 2, where

P1 is the average amplitude of a transmitted “one” and

P0 is the average amplitude of a transmitted “zero.”

The extinction ratio is P1/P0. Combining these equa-

tions results in P1 = (2 x PAVE x Er) / (Er + 1) and P0 =

(2 x PAVE) / (Er + 1). In this example, P1 = 1.6mW and

P0 = 0.4mW. The optical modulation is 1.2mW. The

modulation current required to produce this output is

1.2mW / η = (1.2mW) / (0.1mA/mW) = 12mA. The

Typical Operating Characteristics show that RMODSET

= 3.9kΩ yields the desired modulation current.

3) Determine the value of ROSADJ:

Using the Allowable ROSADJ Range vs. Modulation

Current graph in the Typical Operating Characteristics,

a 5.6kΩ resistor is chosen for 12mA of modulation cur-

rent. The maximum ROSADJ values given in the graph

minimize aberrations in the waveform and ensure that

the driver stage operates fully limited.

4) Determine the value of RBIASSET:

The automatic power control circuit can adjust the bias

current 40mA from the initial setpoint. This feature

makes the laser driver circuit reasonably insensitive to

variations of laser threshold from lot to lot. The bias set-

ting can be determined using one of two methods:

A) Set the bias at the laser threshold.

B) Set the bias at the midpoint of the highest and low-

est expected threshold values.

Method A is straightforward. In the second method, it is

assumed that the laser threshold will increase with age.

The lowest threshold current occurs at 0°C when the

laser is new. The highest threshold current occurs at

+70°C at the end of the product’s life. Assume the laser

is near the end of life when its threshold reaches two-

times its original value.

Lowest Bias Current:

ITH + ∆ITH = 20mA + (0.35mA/°C)(-25°C) = 11.25mA

Highest Bias Current:

2 x ITH + ∆ITH = 40mA + (0.35mA/°C)(+45°C) = 55.8mA

_______________________________________________________________________________________ 9

Share Link: