PLD datasheet(12/21 Pages) WAVELENGTH

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PLD SERIES LASER DIODE DRIVER

ONBOARD ADJUSTMENTS AND CONTROLS

Onboard controls are on the top of the PLD and must be set

according to the operation mode. The controls are illustrated

Figure 12.

Electronics

avelength

PLD SERIES

PD RANGE

MODE

Operating Mode *

Output Adjust (12-turn)

Current Limit Adjust (12-turn)

Output Enabled LED (Green = On)

Current Limit Status

(Red = Current Latched Off)

PD Range *

L = 15 – 500 µA

H = 50 – 5000 µA

P = Constant Power

I = Constant Current

LASER DIODE

DRIVER

OUTPUT

ADJUST

LIMIT I

ADJUST

OUTPUT

ENABLED

LIMIT I

* DO NOT change switch positions while the output

is enabled; Doing so may damage the laser diode.

PD Cathode

PD Anode

LD Cathode

LD Anode/+LD Supply

GND

+5V

Analog Input

P Monitor

I Monitor

Common

LIM I Monitor

LIM I Status

LD Enable

PD Aux

Aux V+

Figure 12. PLD Driver Adjustments and Controls

SET THE CONTROL MODE

Set the MODE switch to P (left) for CP-mode operation, or

to I (right) for CC-mode. Constant Power mode operation

requires a photodiode feedback loop from the laser diode.

! Donotswitchthecontrolmodewhiletheoutputis

enabledanddrivingalaserdiode.Thelaserdiode

may be damaged or destroyed.

SET THE PHOTODIODE RANGE

Two photodiode feedback current ranges are available on

the PLD drivers. Reference the datasheet for your laser

diode to find the nominal photodiode current, and set the

PD RANGE switch as follows:

• L (left) = Low Range, PD current 15 – 500 µA

• H (right) = High range; PD current 50 – 5000 µA

! DonotswitchthePDRangewhiletheoutputis

enabledanddrivingalaserdiode.Thelaserdiode

may be damaged or destroyed.

CALCULATE THE MONITOR VOLTAGES

Refer to the datasheet for your laser to determine the

maximum forward current, and calculate the LIM I Monitor

voltage using this equation and the transfer function found

Table 2 on page 5:

LIM I Mon = ILIMIT / Transfer Function

If you are using the PLD in Constant Current mode, calculate

the monitor voltage for the drive current setpoint. Refer

to the datasheet for your laser to determine the nominal

forward current, and calculate the I Monitor voltage using

the transfer function found in

Table 2:

I_MON = ILD / Transfer Function

If you are using the PLD in Constant Power mode, calculate

the P Monitor voltage. Refer to the laser diode datasheet

to determine the nominal photodiode current at the desired

operating point. Calculate the P Monitor voltage using the

transfer function found in

Table 2:

P_MON = IPD / Transfer Function

SET THE CURRENT LIMIT

Connect the positive lead of the digital voltmeter to the

LIM I Monitor terminal or evaluation board test point, and

the negative lead to the COMMON terminal.

Reference

Figure 7 for switch and control locations on the

PLDEVALPCB board. Configure the PLD and PLDEVALPCB

board:

• Set the OUTPUT switch to LASER DISABLE

• Set the POWER switch to ON

• Set the MONITOR switch to I MONITOR

• Set the OUTPUT ADJUST trimpot to zero by turning at

least 12 turns counter-clockwise.

• Set the current limit by turning the LIMIT I ADJUST

trimpot until the voltage displayed on the multimeter

matches the value calculated above.

Switch off power on the evaluation board, then switch off

the power supply.

The PLD controllers trip the current limit circuit below the

expected limit level, by 0.2 V on the monitor. To trip the

current limit at exactly the desired current level, refer to

Set the Current Limit More Accurately on page 14 to

fine-tune the current limit.

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