THORLABS EK2000 User manual
EK2000
OEM Laser Diode Driver
Evaluation Kit
User Guide
OEM Laser Diode Driver Evaluation Kit
Table of Contents
Chapter 1 Warning Symbol Definitions ...........................................1
Chapter 2 Safety.................................................................................2
Chapter 3 Description........................................................................3
3.1. Using the EK2000 ..........................................................4
3.1.1. Minimal Configuration............................................................... 4
3.1.2. CW Operation........................................................................... 6
3.1.3. Analog Modulation.................................................................... 7
3.1.4. External Modulation Operation.................................................. 8
Chapter 4 LD2000R Overview.........................................................10
4.1. Slow Start Circuit ........................................................10
4.2. Limit Current Circuit ....................................................10
4.3. Constant Power Feedback Loop ...................................10
4.4. Theory of Operation....................................................11
4.5. Setup..........................................................................13
4.5.1. Setting the Feedback Resistor.................................................15
Chapter 5 Specifications.................................................................16
Chapter 6 Mechanical Drawings.....................................................17
Chapter 7 Regulatory.......................................................................19
Chapter 8 Thorlabs Worldwide Contacts.......................................20
OEM Laser Diode Driver Evaluation Kit Chapter 1: Warning Symbol Definitions
Page 1 Rev F, May 21, 2018
Chapter 1 Warning Symbol Definitions
Below is a list of warning symbols you may encounter in this manual or on your
device.
Symbol
Description
Direct Current
Alternating Current
Both Direct and Alternating Current
Earth Ground Terminal
Protective Conductor Terminal
Frame or Chassis Terminal
Equipotentiality
On (Supply)
Off (Supply)
In Position of a Bi-Stable Push Control
Out Position of a Bi-Stable Push Control
Caution: Risk of Electric Shock
Caution: Hot Surface
Caution: Risk of Danger
Warning: Laser Radiation
Caution: Spinning Blades May Cause Harm
OEM Laser Diode Driver Evaluation Kit Chapter 2: Safety
2468-D01 Page 2
Chapter 2 Safety
All statements regarding safety of operation and technical data in this instruction
manual will only apply when the unit is operated correctly.
SHOCK WARNING
Warning is given when there is danger of injury to users.
CAUTION
Caution is given when there is a possibility of damage to the product.
WARNING
Given when there is danger of injury to users.
OEM Laser Diode Driver Evaluation Kit Chapter 3: Description
Page 3 Rev F, May 21, 2018
Chapter 3 Description
The EK2000 integrates the LD2000R with an evaluation board pre-wired for use
with a laser diode with an A-style pin configuration and a connection for a power
supply. The EK2000 allows users to quickly set up the LD2000R with a laser and
DC power supply without having to develop a custom PCB or extensive hand
wiring.
All of the LD2000R features are supported with convenient, easy to use
connector interfaces. The LD2000R is a low-noise, stable laser diode current
source that can be operated with laser diodes having a common laser anode and
monitor photo diode cathode (Pin Style A). The driver operates in an automatic
power control (APC) mode using the built-in monitor photo diode integrated in the
laser diode for feedback. On board trim pots are provided for controlling the laser
power and current limit. Both functions can also be controlled via an external
voltage source. The LD2000R supports a wide range of laser diodes with drive
currents up to 100 mA and photo diode currents from 20 µA to 2 mA. The
LD2000R also has an external modulation input to support applications that
require modulating the laser output.
Figure 1 Compatible LD Pin Codes
NOTE
The Laser Diode case must remain floating with respect to both the power
supply ground, and the chassis ground.
NOTE
Read the section on using the EK2000 (page 4) before attempting to operate
the EK2000.
WARNING
The EK2000 uses CMOS circuitry to minimize power drain. Use anti-static
precautions while handling the LD2000R to prevent permanently damaging
the device.
OEM Laser Diode Driver Evaluation Kit Chapter 3: Description
2468-D01 Page 4
3.1. Using the EK2000
The diagram below illustrates the typical set up for the EK2000. The user needs
to supply their own power supply. We recommend the LDS2 9 VDC Power
Supply.
Figure 2 Setup Diagram
Important Note on Power Supplies
Although the LD2000R provides over 60 dB of power supply rejection, a clean
DC power supply free of excessive transients and surges is required for ultimate
laser protection.
3.1.1. Minimal Configuration
To set the EK2000 up for the simplest configuration (CW mode, no external
modulation) follow the steps below:
1. Connect a DC power supply to P2.
2. Connect your laser to P1.
3. Install jumpers in P5 and P6 to enable the on-board trim pots (default
position).
4. Install a jumper in P10 to disable the external modulation.
5. Install the appropriate value resistor in RFEXT (see LD2000R
Application Notes).
The EK2000 is now set up to operate the laser in a CW mode using the
LD2000R on-board trim pots to control the laser drive current.
NOTE
For all modes of operation, we recommend using a linear DC power supply or
battery. Although the LD2000R provides over -60 dB of power supply
suppression, switch-mode power supplies should be avoided due to the
inherent transients in their output.
OEM Laser Diode Driver Evaluation Kit Chapter 3: Description
Page 5 Rev F, May 21, 2018
Table 2. EK2000 Component Descriptions
Ref
Des
Description
Pin
EK2000
Pin
LD2000R
Connection
P1
Laser Connections
1
2
3
11
12
13
Laser Diode Anode
Monitor Photodiode Anode
Laser Diode Cathode
P2
Power Supply
Hookup
1
2
9
10
Power Supply Positive +8 to
+12 VDC
Power Supply Return
P3
Power Limit External
Trim pot (50 k)
1
2
3
7
6
10
CW Terminal (Vref 2.5 V)
Wiper Terminal
CCW Terminal (GND)
P4
Current Limit External
Trim pot (50 k)
1
2
3
7
14
10
CW Terminal (Vref 2.5 V)
Wiper Terminal
CCW Terminal (GND)
P5
On-Board Current
Limit Trim pot
Enable.
1
2
14
15
Jumper these 2 pins to
enable on-board trim pot.
P6
On-Board Power
Limit Trim pot
Enable.
1
2
5
6
Jumper these 2 pins to
enable on-board trim pot.
P7
Photodiode Amplifier
Output Monitor
Attach a DVM to
these pins to monitor
the photo diode
transimpedance amp
output.
1
2
8
12
These pins can be used to
monitor the laser photo
diode feedback current. The
voltage sensed here will be
determined by the
transimpedance gain :
(i.e. V= IMON * 20 k*
RFEXT / (20 k+ RFEXT) )
P8
Current Limit Monitor
(40 mA/V)
1
2
18
10
LIMIT OUT
GND
P9
ON/*OFF
Shorting these two
pins will disable the
laser output.
1
2
17
10
ON/*OFF input
GND
P10
Analog Modulation
Input
If external analog
modulation is not
required, these 2 pins
must be jumpered
together.
1
2
3
10
ANALOG MOD
GND
OEM Laser Diode Driver Evaluation Kit Chapter 3: Description
2468-D01 Page 6
Ref
Des
Description
Pin
EK2000
Pin
LD2000R
Connection
C2
Power Supply
Bypass
(0.1 F ceramic
recommended)
1
2
9
10
Unpolarized
CDLY
Adding an external
capacitor will extend
the turn-on delay
cycle.
1
2
17
10
The pad nearest the
LD2000R has a positive
potential. Attach the + lead
of an electrolytic to this pad.
RF
EXT
An external resistor
can be added here to
modify the
transimpedance gain
of the LD2000R
photo diode feedback
circuit. This is
connected in parallel
with the internal
20 kresistor.
A mounting location
is also provided
above the RF EXT to
mount a trim pot (e.g.
Bournes 3266 series,
1 M) to provide
continuous adjustable
transimpedance gain.
1
2
8
12
Unpolarized
(Refer to the LD2000R
Application Notes for a
detailed description of the
photo diode feedback circuit
operation.)
RPU
A 15 kresistor must
be installed here in
order to operate a
laser.
1
2
17
10
Unpolarized
3.1.2. CW Operation
To operate the EK2000 in a CW mode, do the following steps:
1. Connect your laser diode to the pre-wired connector assembly.
2. Attach a suitable DC voltage supply across P2 on the Eval Board. A 1’
long prewired cable assembly will be provided. Connect the + voltage to
the red wire and the ground to the black wire. The power supply will be
bypassed near the LD2000R with a 10 µF tantalum capacitor (C1) and a
0.1 µF ceramic capacitor (C2).
3. Short P6 on the Eval Board to use the on-board PD Current Trim pot
(factory default setting).
4. Short P5 on the Eval Board to use the on-board Current Limit Trim pot
(factory default setting).
OEM Laser Diode Driver Evaluation Kit Chapter 3: Description
Page 7 Rev F, May 21, 2018
5. Short P10 on the Eval Board to set analog modulation to FULL ON
(factory default setting).
6. Short P9 on Eval Board to set ON/*OFF to off position (factory default
setting).
7. Turn both the PD Current Trim pot and the Current Limit Trim pot
counter-clockwise 20 turns each to set these at their minimum operating
points.
8. Turn the DC power supply on and use a voltmeter to monitor the LIMIT
OUT (P8 on Eval Board).
9. Adjust the Current Limit Trim pot clockwise slowly while observing the
LIMIT OUT to set the maximum operating current for your laser (refer to
laser manufacturer's data sheets). Note: this output is 40mA/V.
10. Remove the shorting jumper across P9. Using a calibrated power meter
to monitor the diode laser output, slowly adjust the PD Current Setpoint
trim pot clockwise to obtain the desired operating power level. The laser
will begin to emit upon reaching the drive current threshold.
3.1.3. Analog Modulation
To operate the EK2000 analog modulation feature, follow the setup procedures
for CW Operation to establish the laser operating conditions. Once the EK2000
has been setup for your laser, remove the shorting jumper from P10 and apply a
positive voltage from P10-VMOD to P10-GND to modulate the laser.
1. The analog modulation voltage has a negative transfer function
characteristic. That is, at 0 volts, the laser is fully on, at 2.5 volts the
laser should be fully off.
2. The linear operating range of the analog modulation is determined by
the transimpedance gain of the PD Amplifier, RF. The appropriate
transimpedance gain for your laser can be calculated as follows:
V
Where IMON is the photo diode current specified by the laser
manufacturer for the maximum operating output power. Note: the
LD2000R includes an internal 20Kresistor. RFis the net resistance of
the internal 20Kresistor with any external resistance added in parallel
on pins 8 and 12. To calculate the external resistance (RFext) needed to
operate at a particular monitor current (IMON), use the following equation:
OEM Laser Diode Driver Evaluation Kit Chapter 3: Description
2468-D01 Page 8
3.1.4. External Modulation Operation
The laser output power can be controlled via an external modulation voltage
while operating in the Constant Power Mode. The laser output is inversely
proportional to the modulating voltage with 0 V being the laser fully on and 2.5 V
turning the laser fully off.
To use the external modulation, perform the following steps:
1. Set up the LD2000R for Constant Power.
2. Attach an external modulation source (e.g. function generator, D/A
converter, etc.) to the Analog Modulation Input (P10).
3. Apply power to the EK2000 and adjust the modulation input amplitude
and frequency for the desired output.
4. The laser output will now be controlled by the external modulation
voltage.
The graph above describes the characteristic of the modulation voltage. If the
LD2000R is set up to match a particular laser, the solid curve would represent
the output power of the laser as a function of the modulation voltage. A couple of
notes of interest:
1. If the PWR Limit control is set below the maximum output power, the
laser output will plateau (clip) at the PWR Limit level for modulations
below the PWR limit.
2. If the total feedback gain, RF, is not optimized for the operating laser,
the laser turn off point of the output will be different than 2.5V (usually
The turn-off
voltage is
dependent on
matching Rfext to
the laser. If the
feedback gain is
too high, the laser
will turn off at a
lower voltage
(Voff = RF(IMon),
where RF=RF EXT
in parallel with
20 kΩ).
Clipping due to
Current Limit
being set too
low.
OEM Laser Diode Driver Evaluation Kit Chapter 3: Description
Page 9 Rev F, May 21, 2018
somewhere below 2.5V since the default feedback gain is usually too
high for most lasers).
3. If the feedback gain is too low for a laser (i.e. the maximum laser power
can be reached at a point somewhere below the maximum setting of
PWR Limit, than use care to set the PWR Limit control to the maximum
desired operating power before applying the modulating voltage.
The table on page 14 lists the descriptions of all the pin outs of the LD2000R.
The following sections discuss the operation of the LD2000R.
OEM Laser Diode Driver Evaluation Kit Chapter 4: LD2000R Overview
2468-D01 Page 10
Chapter 4 LD2000R Overview
The LD2000R is composed of three independent circuits: slow start circuit, limit
current circuit, and output control circuit. Each is described below.
4.1. Slow Start Circuit
The slow start circuit is used to monitor the supply voltage and keep the laser
output off until the power supply stabilizes. The slow start circuit uses a voltage
reference and a comparator to monitor the supply voltage. An internal 2.5 V
reference is compared to the voltage at the ON/OFF pin (pin 17). When this
voltage exceeds 2.5 V, the laser is enabled. The comparator input (pin 17,
ON/OFF) has an input impedance of 20 kΩ. This resistance is used with an
external resistor to form a voltage divider that sets the LD2000R dropout voltage.
For most applications a 15 kΩ resistor tied from the 12 V power supply to the
ON/OFF pin which disables the laser when the power supply drops below 4.5 V
is adequate.
Note, the ON/OFF pin can also be used to disable the laser by pulling this pin low
to 0 V.
The slow start circuit uses an internal time constant formed by a 1 MΩ and a
1 µF capacitor to yield a 50 ms turn on delay. This can be extended by adding an
external capacitor to the SLOW_START pin.
4.2. Limit Current Circuit
The limit current circuit is a constant current source which can be set by the on-
board trim pot or an external control voltage. This determines the maximum drive
current that can be supplied to the laser. The transfer function for this control is
40 mA/V. The current limit also determines the laser current when operating in
the constant current mode.
4.3. Constant Power Feedback Loop
The constant power feedback loop circuit uses the laser monitor photodiode
current (which is proportional to the laser output power) to regulate the laser
output power. An internal transimpedance amplifier converts the photodiode
current to a voltage used by the feedback circuit. The feedback loop varies the
drive current to the laser such that the voltage derived from the photodiode
monitor current matches an adjustable setpoint voltage (described below). The
laser output can be adjusted by varying the setpoint voltage.
When the current limit is set higher than the laser current needed by the
feedback loop the laser is operating in a constant power mode. If the current
needed by the feedback loop is higher than the current limit, the laser drive
current will be clipped to the current limit and the laser will then be operating in
the constant current mode.
OEM Laser Diode Driver Evaluation Kit Chapter 4: LD2000R Overview
Page 11 Rev F, May 21, 2018
The photodiode transimpedance amplifier has an internal gain of 20 kΩ which
yields a 50 µA/V output. Since the maximum voltage of the feedback loop is 2.5
V, this limits the maximum photodiode current to 125 µA. This upper limit can be
easily increased by adding an external resistor (see page 15).
The setpoint voltage used by the feedback loop is the difference between the PD
CURRENT SETPOINT voltage and the Analog Modulation Voltage as follows:
The control loop integrator has a time constant of approximately 16.5 µs set by a
0.033 µF integrating capacitor. The loop time constant can be extended by
adding an external capacitor across CX1 and CX2.
Note all control signals are based on the photodiode current. The user must refer
to the manufactures spec sheets of the particular diode that will be used to
correlate this to the laser output power.
4.4. Theory of Operation
The LD2000R uses the internal monitor photodiode provided on most low power
diode lasers for feedback when operating in the Constant Power Mode. The
following figure is a block diagram of the LD2000R laser driver.
Figure 3 LD2000R Simplified Block Diagram
OEM Laser Diode Driver Evaluation Kit Chapter 4: LD2000R Overview
2468-D01 Page 12
The laser power is regulated through an integrating feedback loop. The setpoint
of the feedback is determined by the PWR LIMIT control trimpot and the
OUTPUT ADJUST knob (in external modulation mode, the external voltage is
used in place of the OUTPUT ADJUST). An internal transimpedance amplifier
converts the laser feedback current to a voltage that is used as the error signal
for the feedback loop.
Since all analog signal levels are based on a 2.5 V internal reference, we will use
this to derive the feedback gain setting resistor value:
The LD2000R has an internal transimpedance gain of 20 k. Without a user
installed feedback resistor, the transimpedance gain is:
and VError is equal to:
where IMon is the feedback monitor photocurrent. The total transimpedance gain
should be set so that the photocurrent at the maximum laser power equals 2.5 V.
Since VError has a maximum value of 2.5 V, we can derive the value of an
external feedback resistor needed to set the transimpedance for any laser:
where RFis the transimpedance gain needed, and IMon is the monitor
photocurrent for your laser.
solving for RF EXT,
OEM Laser Diode Driver Evaluation Kit Chapter 4: LD2000R Overview
Page 13 Rev F, May 21, 2018
4.5. Setup
The LD2000R is packaged as a component which, with minimal external
components, can be integrated into a system to make a complete laser diode
driver system. We recommend using printed circuit board construction to achieve
optimum results. The pinouts for the LD2000R are provided in Figure 1 and
described below. The LD2000R can be used with A, D, or F style diodes. The D
and F style diodes will need to be configured like an A style diode (see page 17
for diagrams). Please note that the EK2000 is not compatible with the F Pin
Style.
Figure 4 LD2000R Pin Out
OEM Laser Diode Driver Evaluation Kit Chapter 4: LD2000R Overview
2468-D01 Page 14
Pin
Name
Description
1
CX1
These pins are provided for connecting an external capacitor to
the control loop integrator to extend the integrator time constant.
This may be necessary to get maximum bandwidth when using
TTL modulation. Connect the positive terminal of the cap to CX2.
2
CX2
3
Analog
Modulation
This pin is used with an external voltage signal source to provide
analog modulation. The transfer function (referenced to the
photodiode current) is -50 µA/V with 0 V being the laser
completely on. The laser output decreases as this voltage
increases with the laser being completely off at 2.5 V. Connect
this pin to ground when not using the analog modulation.
4
Slow Start
This output pin is high during the startup period and goes low
when the laser is enabled. It can be used as a LASER
EMISSION indicator. An external capacitor can be connected
from this pin to ground to extend the slow start delay time.
Note: this output will not drive an LED directly and must be
buffered. Contact Tech Support for more details.
5
PD Current
Trimpot
This pin is connected to the wiper of the on-board PD Current
Trimpot. Connect this pin to the PD Current Setpoint to control
the PD current with the on-board trimpot.
6
PD Current
Setpoint
This pin controls the PD Current according to a transfer function
of 50 µA/V with 0 V being the laser is completely off (0 PD
current). The laser output increases as this voltage increases.
7
REF Out
This is a buffered 2.5V voltage reference.
8
PD AMP Out
This is an analog voltage proportional to the photodiode current
and referenced to one half the supply voltage as follows:
,
where RF= PD Amp Transimpedance gain (internal 20 kin
parallel with RF EXT)
9
V+
Positive supply voltage (8 to 12 VDC).
10
GND
Power supply common.
11
LD A/PD K
Common laser diode anode, photodiode cathode.
12
PD A
Photodiode anode.
13
LD K
Laser diode cathode.
14
Limit
Setpoint
This voltage determines the maximum laser drive current
according to the transfer function 40 mA/V.
15
Limit Trimpot
This is connected to the wiper of the Limit Current trimpot.
Connect this to the Limit Setpoint pin to use the on-board trimpot
to set the current limit.
16
Not used
This must be tied to ground to operate the laser.
17
ON/OFF
This pin is used to externally turn the laser on and off through
the slow start circuit and to set the low voltage dropout point. It
has an internal 20 kΩresistor to ground. Connect a 15 kΩ
resistor to the power supply voltage to set the dropout voltage to
4.5 V.
18
Limit Out
This is an output voltage proportional to the limit current with a
transfer function of 40 mA/V. Use this pin to assist in setting the
laser current limit.
OEM Laser Diode Driver Evaluation Kit Chapter 4: LD2000R Overview
Page 15 Rev F, May 21, 2018
4.5.1. Setting the Feedback Resistor
The LD2000R is configured at the factory for a maximum feedback gain. This
gain setting is appropriate for lasers that have low monitor currents in the range
of 20 to 120 A.
For most lasers, the photodiode current is greater than 120 A and the feedback
gain will have to be reduced to drive the laser at full drive current. This can be
done by following the procedure below.
1. Determine the appropriate feedback gain using the following calculation:
where RF EXT is the external gain setting resistor to be added in ohms
and IMON is the monitor current for a particular laser in Amps.
2. Pick the nearest standard value resistor (0.25 W, 5% or better).
3. Connect RF EXT across pins 8 and 12 of the LD2000R.
SHOCK WARNING
The LD2000R uses CMOS circuitry to minimize power drain. Use anti-static
precautions while handling the LD2000R to prevent permanently damaging
the device.
0.1 1 10
0.1
1
10
100
1 103RFext vs. PD Monitor Current
PD Monitor Current (mA)
RFext (kohms)
OEM Laser Diode Driver Evaluation Kit Chapter 5: Specifications
2468-D01 Page 16
Chapter 5 Specifications
Specification
Value
Current Output
Limit Current Control
Trimpot or External Analog Voltage
Limit Current Range
0 to 100 mA
Limit Accuracy
±1%
Compliance Voltage
Power Output
Photodiode Current Control
Trimpot or External Analog Voltage
Photodiode Current Range
20 to 125 A (Factory Configured1)
Long Term Drift (24 hrs)
<0.1%
Temperature Coefficient
<100 ppm/°C
Analog Bandwidth
3 db Bandwidth (Nominal)
10 kHz2
Power Supply
Supply Voltage (V+)
8 to 12 VDC
Supply Current
30 mA Plus Laser Current
General
Dimensions
2" x 1.3" x 0.5"
Operating Temperature
-20 to 60 °C
Storage Temperature
-65 to 150 °C
Packaging
PCB DIP, Plastic Encapsulated
1
Higher photodiode currents are easily supported by adding a single external resistor.
2
The actual bandwidth is laser dependent.
OEM Laser Diode Driver Evaluation Kit Chapter 6: Mechanical Drawings
Page 17 Rev F, May 21, 2018
Chapter 6 Mechanical Drawings
Figure 5 EK2000 Mechanical Drawing
OEM Laser Diode Driver Evaluation Kit Chapter 6: Mechanical Drawings
2468-D01 Page 18
Figure 6 LD2000R Mechanical Drawing
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