LDDEVALP datasheet(13/28 Pages) WAVELENGTH

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LDD P SERIES LASER DIODE DRIVER

adjusT LaseR diode cuRRenT Via moduLaTion (oPTionaL)

There are two ways to utilize the Modulation Input to adjust

the laser diode current remotely:

•

Connect an external trimpot or potentiometer to pin 3.

See upper half of

Figure 15.

•

Connect a signal generator to pin 3. See lower half of

Figure 15.

External

Trimpot

V+ (pin 8)

Bandgap

Voltage

Reference

CURRENT

FEEDBACK

CURRENT

MONITOR

MODULATION

GND

CURRENT

FEEDBACK

CURRENT

MONITOR

MODULATION

GND

Signal

Generator

Ground

Figure 15. Two separate ways to control the laser diode

current remotely.

Upper: External Trimpot connected to pin 3.

Lower: Signal Generator connected to pin 3.

The modulation input adjusts the laser diode current by

reducing the laser diode current from the setting determined

by the Output Current Adjust trimpot proportional to the

voltage applied to pin 3.

The modulation current (I

MOD) is given by Equation 4.

Equation 4. I

MOD = IOP + VPIN3 (TFMOD )

where TF

MOD is the laser diode transfer function found in

Table 3. Recall that TF

MOD is negative.

CAUTION: The modulation input voltage must always be

maintained within the power supply voltage range between

pin 8 and pin 4. A voltage on the modulation input below

ground may produce excessive laser diode currents.

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