LDTC 2SLASH2O datasheet(19/25 Pages) WAVELENGTH

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LDTC2/2 LASER DIODE DRIVER 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 4).

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 technical note

TN-TC01: Optimizing Thermoelectric Temperature Control Systems at

www.teamwavelength.com/download/applicationtechnotes/tn-tc01.pdf

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

“Configuring heating and cooling current limits” on page 9 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/

LDTC does not respond to

external temperature setpoint

input.

The EXT T SET signal is below the

minimum signal value of 0.3 V.

If the R TC 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 R TC 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 cooler, which can alternately heat and cool the load to maintain

a more precise setpoint temperature.

Setpoint is 1 V even when the

Tset trimpot is fully OFF.

Failsafe circuit has been activated

due to low setpoint.

Increase the temperature setpoint to a value above 0.3 V. Once the Tset

value becomes greater than 0.3 V, the failsafe circuit will be disabled and the

setpoint will be at the set value.

LDTC 2/2O Datasheet(PDF) 19 Page - Wavelength Electronics, Inc.

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