Wavelength Electronics LDTC0520 Datasheet And Operating Manual Download Page 24

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LDTC0520 / LDTC1020 LASER DIODE AND TEMPERATURE CONTROLLER

TROUBLESHOOTING
LASER DRIVER

PROBLEM

POTENTIAL CAUSES

SOLUTIONS

Driver will not switch on

Improperly configured power supply

Carefully check the wiring diagram on

page 2

. Make sure the power supply

polarity is not reversed.

Power supply voltage too low

The LDTC includes brown-out protection circuitry that disables the laser driver

if the power supply voltage falls below 2.7 V. Make sure the power supply

voltage is correct.

Output will not enable

Improperly configured enable switch

on the LDTC

If the LDTC is configured to use the LD SHD remote enable input, the onboard

Enable/Disable switch must be set to EN (enable). Make sure this switch is

properly set.

Remote Enable signal is not correct

To enable the laser output, the LD SHD pin must be grounded. Float the pin, or

input a 3 to 5 V signal, to disable the output.

Laser output power too low in

Constant Current mode

Laser current setpoint too low

Increase the setpoint either by adjusting the I SET trimpot clockwise, or by

increasing the signal voltage on the EXT LD SET input (pin J2‑5).

Laser current limit too low

Refer to

page 13

for instructions on setting the laser driver current limit.

Laser driver is compliance limited

Check the laser diode specifications to determine the forward voltage (V

Make sure that the LDTCxx20 is not compliance limited. Refer to the Electrical

Specifications table on

page 6.

If the driver is compliance limited, V

DD_FL

may need to be increased.

Verify that the LDTCxx20 will be operating

within the Safe Operating Area if V

DD_FL

is increased.

Laser does not reach desired

output in Constant Power mode

Laser current limit too low

Check the laser diode datasheet to determine the approximate laser drive

current at the desired optical power output level. Then verify that the current

limit is set slightly higher than that. Refer to

page 13

for instructions on

setting the laser driver current limit.

Photodiode feedback current is out

of range for the LDTC

Refer to the laser diode datasheet to determine the approximate photodiode

(PD) current at the desired output power level. If the PD current exceeds

the LDTC PD current range, the LDTC will require modification. Contact the

Wavelength Electronics Sales department for assistance.

Summary of Contents for LDTC0520

Page 1: ...ntrol module is known for precision and reliability Independent cooling and heating current limits allow the LDTC to be used with thermoelectric coolers or resistive heaters and either negative or positive temperature coefficient sensors FEATURES AND BENEFITS Small package size Single or dual supply operation LD current range 500 mA or 1 A Compatible with Type A and B lasers Slow start laser diode...

Page 2: ...ect diagram with a laser diode separate power supplies and a thermoelectric cooler The LDTCxx20 is compatible with Type A and Type B lasers but will not drive Type C lasers see Figure 3 VDD_FL VDD_WTC VS GND SP1 SP2 LD SHD Enable LD current COM EXT LD SETpoint COM LD P Monitor LD I Monitor ACT T Monitor SET T Monitor EXT T SETpoint COM LDC PDA Spare LDA COM TEC TEC SEN SEN COM J1 J2 J3 VDD_WTC VDD...

Page 3: ...resistor value to change the output current 1 Ω 2 W Figure 5 Constant Power Mode Test Load NOTE To determine the actual drive current measure the voltage drop across the 1 Ω resistor Do not insert an ammeter in series with the output circuit doing so may cause instability in the control loop To stay within the Safe Operating Area while using the test load VS must not exceed 5 V Temperature Control...

Page 4: ...s pin is proportional to the photodiode current Voltage range 0 to 2 V Transfer function shown in Table 2 8 LD I M Blue Laser current monitor output The signal on this pin is proportional to the actual laser output current Transfer function shown in Table 2 9 ACT T M Red Blk Actual temperature sensor voltage monitor output Output voltage equals the voltage drop across the temperature sensor Voltag...

Page 5: ...LIM test point on the circuit board ACT T M 1 V V The ACT T M voltage matches the voltage drop across the temperature sensor SET T M 1 V V The SET T M voltage matches the setpoint voltage set by the onboard trimpot or the EXT T SET input pin J2 11 EXT T SET 1 V V The external temperature setpoint input Table 3 Wiring Diagram Reference and LIM Trimpot Functions SENSOR TYPE LOAD TYPE VDD_WTC AND VS ...

Page 6: ... Term Stability 24 hours 0 011 TAMBIENT 25ºC OUTPUT Peak Current IMAX 495 to 505 990 to 1010 mA Compliance Voltage VDD_FL 0 5 VEXT LD SET V IMAX 500 mA Rise Time 300 nsec ILD 500 mA Fall Time 300 nsec ILD 500 mA Bandwidth Constant Current 2 500 kHz Sinewave input signal Delayed Start 100 msec Slow Start Ramp 15 mA msec Depth of Modulation 99 100 kHz sinewave LD POWER SUPPLY Power Supply Voltage VD...

Page 7: ...TORS Internal T SET Voltage Range 3 0 to 4 V Product Revision C EXT T SET Input Impedance 1 MΩ EXT T SET Input Voltage Range 0 to 3 3 V EXT T SET Input Damage Threshold 0 to 3 6 V Setpoint vs Actual Temperature Accuracy 0 1 2 4 mV TSET 25ºC 10 kΩ thermistor FEEDBACK LOOP P Proportional Gain 18 20 22 A V I Integrator Time Constant 2 3 4 5 sec 1 When using resistive heaters stability can only be con...

Page 8: ...urrent in order to change the temperature of the sensor that is connected to the thermal load The goal is to make the voltage across the sensor match the setpoint voltage and then keep them equal in spite of changes to ambient conditions and variations in thermal load SAFETY INFORMATION THERMAL DESIGN CONSIDERATIONS SAFE OPERATING AREA DO NOT EXCEED INTERNAL POWER DISSIPATION LIMITS Before attempt...

Page 9: ...ture with minimal overshoot and ringing OPERATING INSTRUCTIONS TEMPERATURE CONTROLLER These instructions are written for the most common application of the LDTCxx20 Controllers driving a laser diode and controlling a Peltier type thermoelectric cooler with a 10 kΩ thermistor sensor We recommend you read and completely understand these instructions before proceeding with wiring the controller Infor...

Page 10: ...erature controller power supplies may need to be isolated from each other or a bipolar supply may be required Refer to page 21 Wavelength recommends using the best quality power supplies available based on your application Noise on the power supply inputs will affect the overall system noise performance particularly on the laser driver VDD_FL 3 12 V Current draw for electronics 10 mA laser VDD_WTC...

Page 11: ... temperature sensor if you are using a resistive heater and or a PTC temperature sensor refer to page 16 for instructions Refer to the TEC datasheet to determine the maximum allowable drive current ILIM As seen in Figure 10 an ammeter directly measures the current through the TEC or RLOAD Prior to applying power ensure that all trimpots are turned completely OFF by turning them a full twelve turns...

Page 12: ... TREF switch to INT down To reference the EXT T SET input set the TREF switch to EXT up J1 J2 J3 Figure 12 Configuration DIP Switches ADJUST THE TEMPERATURE SETPOINT If the LDTC is configured for onboard temperature control the setpoint is adjusted using the T SET trimpot accessible through the hole in the cover The temperature setpoint corresponds directly to the desired voltage drop across the t...

Page 13: ...ent ILIM Measure the exact resistance of the test load RLOAD then calculate the VLIM voltage drop across the test load resistor VLIM ILIM RLOAD 1 Set the I SET trimpot to zero by turning fully counter clockwise at least 12 turns set the I LIM trimpot to full scale by turning it clockwise at least 12 turns Set the CC CP switch to CC Switch on the VDD_FL power supply the FL POWER LED will illuminate...

Page 14: ...nabled and driving a laser diode The laser diode may be damaged or destroyed ADJUST THE LASER OUTPUT SETPOINT If the LDTC is configured for onboard laser control the septoint is adjusted using the ISET trimpot accessible through the hole in the front cover If the LDTC is configured for external setpoint control connect the signal source to Pin J2 5 Example setpoint circuits are shown on page 19 an...

Page 15: ...he load resistor at the limit current VLIM ILIM RLOAD Adjust the thermistor test load to 10 kΩ resistance Place the multimeter leads across the test load resistor Switch on the power supplies Adjust T SET fully counter clockwise to simulate a high temperature setpoint If you are using an NTC sensor If VDD_WTC and VS are tied the LIM A trimpot must be set to zero fully counterclockwise at least 12 ...

Page 16: ...e Heater VDD_WTC and VS Separated WIRE THE LDTC TEMPERATURE CONTROLLER ALTERNATE APPLICATIONS The LDTC can be wired in a number of different configurations using different temperature sensors and load transducers Table 4 identifies which wiring diagram to use for each case If the sensor is not a 10 kΩ thermistor then you must make internal modifications to the LDTC Refer to page 17 for instruction...

Page 17: ...Thermistor 200 kΩ 10 µA Open 1 500 kΩ Thermistor 1 MΩ 2 µA Open 1 100 Ω Pt RTD 2 kΩ 1 mA 100 Ω 10 1 kΩ Pt RTD 2 kΩ 1 mA Open 1 LM335 2 kΩ 1 mA Open 1 AD590 Open Open 1 RBias Sensor Gain Resistor Rs 100 Ω Figure 20 Location of RBIAS and RS Rev C only RBias Sensor Gain Resistor Rs 100 Ω Figure 21 Location of RBIAS and RS Rev A B only Adjust Sensor Gain If the desired temperature setpoint results in ...

Page 18: ... PGAIN in A V from RP use Eq 5 100 5 PGAIN 100000 1 RP To locate RI and RP on Rev C only refer to Figure 22 Figure 22 RP and RI Component Locator Topside of Board Product Rev C only Table 7 lists the suggested resistor values for RI versus sensor type and the ability of the thermal load to change temperature rapidly Table 7 Integrator Time Constant vs Sensor Type and Thermal Load Speed SENSOR TYPE...

Page 19: ...lculate RPD value using Eq 8 IPDMAX is in A and RPD is in Ω IPDMAX 1 8 RPD 3 Change R31 appropriately 4 Replace thermal compound on the FL500 s and reinstall PCB on the supports EXTERNAL SETPOINT CIRCUITS With the TREF and LDREF switches set to EXT up the LDTC will reference the analog inputs for the temperature and laser current setpoints respectively In both cases a benchtop voltage source or DA...

Page 20: ...imit setting The transfer function is found in Table 2 and varies according to the controller model number VLD I LIM ILIM 9 Transfer Function Remove the two screws securing the cover of the LDTCxx20 lift off the cover and locate the test point above the I LIM trimpot refer to Figure 28 for Rev C only and Figure 29 for Rev A B only Connect the positive lead of the DVM to the test point and the nega...

Page 21: ...n the power supply is effectively shorted to ground via the laser diode case The power supply will overheat blow a fuse or otherwise fail To remedy the situation connect the GND pin on connector J1 to the negative terminal of the power supply but not to Earth ground Refer to Figure 31 Internal Laser Driver Electronics LDTCxx20 J1 1 J3 1 J3 2 J3 4 J1 4 CORRECT _ VDD_FL Power Supply Figure 31 Case S...

Page 22: ...e X axis mark the supply voltage VDD_FL Extend a diagonal line from VDD_FL to the intersection of the VDROP and IMAX lines this is the Load Line If the Load Line crosses the Safe Operating Area line at any point the configuration is not safe If the SOAcalculator indicates the LDTC will be outside of the Safe Operating Area the system must be changed so that less power is dissipated within the driv...

Page 23: ...e and bias current should be selected to maximize sensitivity at the target temperature Thermistors provide the best performance particularly for applications where a single setpoint temperature must be accurately maintained For example at 25 C a 10 kΩ thermistor has a sensitivity of 43 mV C whereas an RTD sensor has a sensitivity of 4 mV C Proportional control term is set too high Reduce the valu...

Page 24: ...lockwise or by increasing the signal voltage on the EXT LD SET input pin J2 5 Laser current limit too low Refer to page 13 for instructions on setting the laser driver current limit Laser driver is compliance limited Check the laser diode specifications to determine the forward voltage VF Make sure that the LDTCxx20 is not compliance limited Refer to the Electrical Specifications table on page 6 I...

Page 25: ...ng 22 AWG I O CABLE WCB302 INCLUDED WITH LDTCxx20 Molex KK 7880 Series Connector Housing Molex 10 11 2123 Pin Molex 46999 0101 36 Long 22 AWG PIN WIRE COLOR 1 VDD_FL GREEN 2 VDD_WTC RED 3 VS WHITE 4 GND BLACK PIN WIRE COLOR PIN WIRE COLOR 1 LDC BLACK 6 TEC RED W BLK 2 PDA WHITE 7 TEC ORANGE 3 SP3 BLUE 8 SEN WHT W BLK 4 LDA RED 9 SEN ORG W BLK 5 COM GREEN 10 COM GRN W BLK PIN WIRE COLOR PIN WIRE CO...

Page 26: ...E AND TEMPERATURE CONTROLLER MECHANICAL SPECIFICATIONS DIMENSIONS LDTC0520 LDTC1020 0 125 3 18 1 08 27 4 2 90 73 7 0 15 3 8 2 60 66 0 2 10 53 3 2 35 59 7 0 125 3 18 THROUGH 2 PLS 0 13 3 3 Figure 36 LDTC0520 LDTC1020 Dimensions All Tolerances 5 units in inches mm ...

Page 27: ...ment is subject to change without notice Wavelength will not be liable for errors contained herein or for incidental or consequential damages in connection with the furnishing performance or use of this material No part of this document may be translated to another language without the prior written consent of Wavelength SAFETY There are no user serviceable parts inside this product Return the pro...

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