USBKIT datasheet(13/20 Pages) WAVELENGTH

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PLD10000/PLD12500 LASER DIODE DRIVER

REMOTE LIMIT STATUS LED CIRCUIT

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

in your control system. Connect the LED as shown in

Figure

11.

LIM I Status

+5V

13,14,15

Figure 11. 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

Lim I Mon calculated on page 11.

CHANGE THE PHOTODIODE RANGE,

TYPE A & B LASERS

The photodiode current range and transfer function can be

adjusted using 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 12 shows the internal resistor network of the PLD

photodiode feedback range control; the equations explain

the interaction with the external resistor.

PD Range

Switch

554

5 k

PD Range = L

[µA]

[µA / V]

PD Range = H

2.5 V * 106

R || 500 Ω

Range =

[µA]

[µA / 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 12. 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 2) and AUX V+ (pin 24).

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)

(R || 5 kΩ) is calculated (units are Ω):

(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

• Important Information on Grounding

• Fine Tune Deep Modulation

• Cable Lengths and High Current

• Add Laser Diode Protection for Long Cables

• Additional Noise Filtering

• Revision A & B Timing Characteristics

• Monitor Calibration Circuit

• Product Variations

• Output On/Off and Current Limit Timing

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