LDDEVALP datasheet(12/28 Pages) WAVELENGTH

12 / 28 page

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LDD P SERIES LASER DIODE DRIVER

adjusT LaseR diode cuRRenT

Before beginning, rotate the Output Current Adjust trimpot

fully counter-clockwise, at least 12 turns to zero the setpoint.

Using the desired operating current, I

OP, calculate the

corresponding monitor voltage (V

OP) using Equation 2.

Equation 2. V

PIN 2 = VOP = IOP / (TFCM )

Where, again, the current must be given in mA, and TF

can be found in

Table 3 on page 4.

Then, SLOWLY adjust the Output Current Adjust trimpot

clockwise until the voltmeter attached to the current monitor

(pin 2) reads V

OP.

CURRENT

FEEDBACK

CURRENT

MONITOR

MOD

GND

- +

OUTPUT

CURRENT ADJUST

SLOWLY

VOLTMETER

Figure 12. Set the Output Current Adjust trimpot to the

operating voltage.

disaBLe LaseR diode cuRRenT

To disable current, let pin 3 float or connect it to V+.

Figure 13 shows an example of how to wire a switch to the

LDD P to enable/disable current.

A residual current is present in the laser

diode when disabled. DO NOT DISCONNECT

THE LASER DIODE UNLESS POWER IS

REMOVED FROM V+ AND GROUND.

CURRENT

FEEDBACK

CURRENT

MONITOR

MOD IN

GND

V+

FEED

BACK

LD ANODE

CATHODE

0.1 µF

This capacitor

debounces mechanical

switches connected

to the MOD input.

Switch

OPEN

CLOSED

Output

Off

Figure 13. Disable current by opening the switch (as shown)

or floating pin 3.

VeRify PhoTodiode cuRRenT LeVeL (oPTionaL)

If you wired an external photodiode (see

Figure 6 &

Figure 7), attach the leads of a voltmeter across the external

resistor as shown in

Figure 14.

- +

LDD 1P models

- +

LDD 2P models

LASER

DIODE

EXT

IPD

EXT

IPD

LASER

DIODE

EXT

IPD

EXT

IPD

V+

RPD

VOLT

METER

VOLT

METER

Figure 14. Connect the voltmeter across the external

resistor.

To find the actual photodiode current, use

Equation 3

below. This value may vary depending on the temperature

of the laser diode. A laser diode with a temperature above

25°C will produce less photodiode current than one at or

below 25°C.

Equation 3. I

PD = VEXT / 1kΩ

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