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23

LDTC0520 / LDTC1020 LASER DIODE AND TEMPERATURE CONTROLLER

TROUBLESHOOTING
TEMPERATURE CONTROLLER

PROBLEM

POTENTIAL CAUSES

SOLUTIONS

Temperature is decreasing 

when it should be increasing

–OR–

Temperature is increasing 

when it should be decreasing

The TEC may be connected 

backwards to the LDTC

The convention is that the 

red

 wire on the TEC module connects to TEC+ (pin 6) 

and the 

black

 wire to TEC‑ (pin 5). If your TEC is connected in this manner and 

the problem persists, the TEC module itself may be wired in reverse. Switch off 

power to the system, reverse the connections to the LDTC, and then try again 

to operate the system.

TEC wiring polarity is dependent on temperature sensor type (NTC vs. PTC). 

Verify that the polarity is correct for the sensor type you are using (

Table 3

).

Temperature increases beyond 

the setpoint and will not come 

down

The heatsink may be inadequately 

sized to dissipate the heat from the 

load and TEC module, and now 

the system is in a condition called 

thermal runaway

Increase the size of the heatsink, add a fan to blow air over the heatsink, and/

or reduce the ambient air temperature around the heatsink.

Apply a thin layer of thermal paste or use thermal washers between the load, 

the TEC surfaces, and the heatsink.

The TEC is not adequately sized for 

the thermal load

The heat being generated by the load may be too great for the TEC to 

pump to the heatsink; a larger TEC may be needed.  Consult our Notes 

TN-TC01: Optimizing Thermoelectric Temperature Control Systems

 and 

 

AN‑TC09: Specifying Thermoelectric Coolers

 for more information.

The temperature of my heater-

based system increases 

without stopping

The current limits might not be 

correctly configured

When using a heater the current limit trimpots LIM A and LIM B must be set 

according to the temperature sensor type you are using. If the load temperature 

increases  past  the  setpoint  and  continues  to  increase,  one  of  the  current 

limit trimpots may have been improperly set. Refer to 

Table 3

 and 

Set the 

Temperature Controller Current Limits (page 11) 

for more information.

Temperature does not stabilize 

very well at the setpoint

Poor thermal contact between 

components of the thermal load

Use thermal paste or washers between the load/TEC and TEC/heatsink 

interfaces. Make sure the temperature sensor is in good thermal contact with 

the load.

Operating outside of the ideal 

region of the temperature sensor

The sensor type 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 value of the proportional term. For more information, contact the 

factory.

Temperature does not reach 

the setpoint

Insufficient current driven to the 

TEC or Heater

Increase the current limit ‑ but DO NOT exceed the specifications of the TEC 

or heater.

The controller does not have 

sufficient compliance voltage to 

drive the TEC or heater

Increase the power supply voltage; be certain to verify that the controller is 

within the Safe Operating Area; the SOA calculator is found at: 

www.teamwavelength.com/support/design-tools/soa-tc-calculator/

The temperature setpoint voltage 

is below the minimum signal value 

of 0.3 V

If  the  setpoint  voltage  falls  below  0.3  V,  the  LDTC  defaults  to  a  “safe 

temperature” setpoint voltage of 1 V (for a 10 kΩ thermistor at 100 µA bias 

current,  the  default  temperature  setpoint  is  25°C).  The  safe  temperature 

setpoint voltage can be changed at the factory if your application requires it. To 

reset the safety circuit, the voltage must be greater than 0.4 V.

LDTC does not respond to 

external temperature setpoint 

input

The TREF switch is improperly 

configured

To configure the LDTC to reference the setpoint signal on pin J2‑11, set the 

 

TREF switch to EXT (up). 

The EXT T SET signal is below the 

minimum signal value of 0.3 V

If  the  EXT  T  SET  signal  falls  below  0.3  V,  the  LDTC  defaults  to  a  “safe 

temperature” setpoint voltage of 1 V (for a 10 kΩ thermistor at 100 µA bias 

current,  the  default  temperature  setpoint  is  25°C).  The  safe  temperature 

setpoint voltage can be changed at the factory if your application requires it. 

To reset the safety circuit, the EXT T SET signal must be greater than 0.4 V.

Temperature is slow to 

stabilize and is not within the 

specifications

Setpoint temperature is set close to 

the ambient temperature

Set the temperature at least 10°C above ambient when using a resistive heater.  

A resistive heater is unable to precisely maintain temperature near ambient 

because once the temperature overshoots the setpoint, the controller turns off 

and relies on ambient temperature to cool the load.  If setting the temperature 

10°C  or  more  above  ambient  is  not  possible,  then  choose  a  thermoelectric 

controller,  which  can  alternately  heat  and  cool  the  load  to  maintain  a  more 

precise setpoint temperature.

Содержание LDTC0520

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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 ...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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 ...

Страница 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...

Страница 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 ...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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...

Страница 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 ...

Страница 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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