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PLD10000/PLD12500 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 in

Figure 10.

MODE

OUT

LIM I

PD RNG

+5V

Analog In

P Monitor

I Monitor

Common

Lim I Mon

Lim I Stat

LD Enable

PD Aux

Aux V+

GND

LD Anode/

+LD Supply

LD Cathode

PD Anode

PD Cathode

N/C

ENBL

OUT

ADJ

LIM I

ADJ

Output Adjust (12-turn)

Current Limit

Adjust (12-turn)

Output Enable LED

(Green = ON)

Current Limit Status

LED (Red = LIMIT)

Operating Mode *

PD Range *

L = 15 – 500 µA

H = 50 – 5000 µA

P = Constant Power

I = Constant Current

* DO NOT change switch positions while the output is

enabled; Doing so may damage the laser diode.

Figure 10. PLD Driver Adjustments and Controls

SET THE CONTROL MODE

Set the MODE switch to P (left) for Constant Power-mode

operation (CP), or to I (right) for Constant Current-mode

(CC). CP-mode operation requires a photodiode feedback

loop from the laser diode.

! DonoTswiTchTheconTroLmoDewhiLeTheouTpuTis

enabLeD anD Driving a Laser DioDe

. The Laser DioDe

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,

Type A and B lasers only

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

! Do noT swiTch The pD range whiLe The ouTpuT is

enabLeD anD Driving a Laser DioDe

. The Laser DioDe

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:

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 Mon pin, or to the LIM I MON test point on the evaluation

board. Connect the negative lead to the COMMON terminal.

Reference

Figure 5 for switch and control locations on

the PLD and PLD10EV board, and configure the PLD and

evaluation board:

• Set the POWER switch to ON

• Set the OUTPUT switch to LASER DISABLE

• Set the MONITOR switch to I MONITOR

• Set the OUTPUT ADJUST trimpot to zero by turning at

least 12 turns counter-clockwise.

• Turn the CURRENT LIMIT ADJUST trimpot clockwise

until the value on the digital multimeter matches the

Lim I Mon 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 13.

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