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PLD SERIES LASER DIODE DRIVER

REMOTE LIMIT STATUS LED CIRCUIT

The LIM I Status feature can be used to drive a remote LED

up to 15 mA in your control system. Connect the LED as

shown in

Figure 13.

LIM I Status

+5V 10

Figure 13. Remote LIM I Status LED

SET THE CURRENT LIMIT MORE ACCURATELY

The current limit circuit is designed with a small hysteresis,

which causes the limit circuit to trip at a slightly lower current

than calculated. To fine-tune the current limit, a small offset

voltage must be factored in. Use this equation to calculate

the hysteresis offset, where V

+5V is the supply voltage:

Offset (V) = (V

+5V – VI_MON) / 25.9

Then add the Offset to V

LIMIT calculated on page 12.

CHANGE THE PHOTODIODE RANGE,

TYPE A & B LASERS

The photodiode current range and transfer function can be

adjusted by adding an external resistor. This feature is useful

when the photodiode current of your laser falls in a range

that does not allow maximum measurement sensitivity on

the PLD driver.

Figure 14 shows the internal resistor network of the PLD

and the equations explain the interaction with the external

resistor.

PD Range

Switch

554

5 k

PD Range = L

A / V

PD Range = H

2.5 V * 106

R || 500 Ω

Range =

A / V

R || 500 Ω

Transfer

Function =

2.5 V * 106

R || 5 kΩ

Range =

R || 5 kΩ

Transfer

Function =

R || 5 kΩ

R + 5000

R * 5000

R || 500 Ω

R + 500

R * 500

PD Anode

COMMON

Internal Electronics

External Electronics

Ω

Figure 14. Adjusting the PD Range,

Type A & B Lasers

CHANGE THE PHOTODIODE RANGE,

TYPE C LASERS

The photodiode range and transfer function can be adjusted

when using Type C lasers by connecting a ¼ W resistor

between the PD Cathode (pin 15) and AUX V+ (pin 1).

The PD current range is calculated (units are amps):

Range = 2.5 V / (R || 5 kΩ)

The transfer function is calculated (units are A / V):

Transfer Function = 1 / (R || 5 kΩ)

The value of (R || 5 kΩ) is calculated as follows (units are Ω):

(R || 5 kΩ) = (R * 5000) / (R + 5000)

ADDITIONAL TECHNICAL

INFORMATION

This section includes useful technical information on these

topics:

• Remote Limit Status LED Circuit

• Set the Current Limit More Accurately

• Change the Photodiode Range, Type A & B Lasers

• Change the Photodiode Range, Type C Lasers

• Change the Analog Input Modulation Transfer Function

• External Setpoint Circuit

•

• Ground the Fan on the PLD1250, PLD5000, and

PLD6500

• Fine Tune Deep Modulation

• Cable Lengths and High Current

• Add Laser Diode Protection for Long Cables

• Additional Noise Filtering

• Monitor Calibration Circuit

• Revision F Timing Characteristics

• Product Variations

• Output On/Off and Current Limit Timing

• Safe Operating Area Calculation

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