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13

PLD SERIES LASER DIODE DRIVER

ADJUST THE OUTPUT CURRENT SETPOINT—

ONBOARD CONTROL

To increase the output current, turn the onboard trimpot

clockwise; turn counter-clockwise to decrease output

current.

While adjusting the output current, measure the voltage on

pin 7, I Monitor. Use the transfer function listed in

Table 2 to

determine the output current from the monitor voltage.

ADJUST THE OUTPUT CURRENT SETPOINT—

ANALOG INPUT

To use the Analog Input on pin 9 to adjust the output current,

refer to Pin Descriptions on

page 5 for specifications.

The analog input signal sums with the onboard trimpot

value.

Refer to the External Setpoint Circuit on

page 15 for an

example analog input circuit. Other circuits, a DAC signal,

or function generator may be used.

COMBINING THE ONBOARD SETPOINT AND

ANALOG INPUT

The Analog Input voltage signal on pin 9 sums with the

onboard trimpot setpoint. This configuration allows the

driver to be configured so that the laser current or power

modulates around a DC setpoint.

If the sum of the two signals causes the PLD to attempt to

drive the output current past the limit, the output will switch

off and indicate a current limit error.

To avoid driving the current to the limit, first set the onboard

trimpot to produce the Constant Current level. Then connect

the modulation source to the Analog Input pin and slowly

increase the modulation amplitude. Monitor the output

current using the I Monitor pin, or by measuring the voltage

across the test load. Do not monitor the voltage across a

laser diode—measurement transients may damage the

laser diode.

CURRENT LIMIT CIRCUIT TRIGGER AND RESET

If the PLD detects current limit, the output will switch off and

the LIMIT I LED on the top of the unit will illuminate red. Set

the Enable switch to OFF, correct the cause of the error,

and then re-enable the output. Toggling the Output Current

switch on the PLDEVALPCB board will clear the current limit

latch.