TC7100, TC7100S

PRECISION TEMPERATURE CONTROLLER

Description

The TC7100 is a low noise ultra stable temperature controller incorporating many features only found in our sophisticated Bench Top Controllers (see our LC8x71 series).

It is intended for the OEM or end user as a Low Cost Building Block for complete temperature control of thermoelectric or resistance elements. The TC7100 supports multiple sensor types as well as providing adjustable output and overcurrent protection. This makes the device an ideal choice for almost any cooling or heating application.

Features:                                                   Applications:

 Supports most sensor types                                Photodiode Temperature Control

 Linear PI Loop                                                        Laser Diode Burn-in Systems

 Adjustable PI Constants                                       Biological Temperature Control

 5 Amp Bipolar Output                                            Precision Temperature Sources

 Low Noise/ Ultra-stable Output                          High Power Laser Diode Cooling

 Output Protection                                                  Etalon Stabilization

 Thermoelectric or Resistive Load

Sensors supported:                                              Package variations:

 2 wire thermistors                                                  TC7100- High dissipation              packages

 RTD's                                                                   TC7100S- Half size package

 AD590 IC sensors

 LM-135/335 IC sensors

Supply Voltage - ( V+, VD+)

 +18V

                   ( V-, VD-)

 -18V

Current output

+/- 5 A

Case temp.-operating

 0 to +50 deg C

Case temp.- storage

 -40 to +70 deg C

                                                             ! Warning !

These devices can generate large amounts of heat. Device failure will occur without proper cooling.

When cooling lasers and laser diodes, always follow the laser manufacturer's warnings to prevent injury and damage.

 Specifications:

Measured at V+ = +15V, V- = -15V, VD+ = +5 V, VD- = -5V, T= 25 deg C 

Parameter

Units

Minimum

Typical

Maximum

Output current range- (bipolar)

A

0- (+/- 5)

Output current ripple and noise

uA

50

200 (see note 1)

Output power

W

See text

Short term stability, 10 min.(note 2)

deg C

0.002

0.005

Long term stability, 24 hrs.(note 2)

deg C

0.005

0.01

Temperature coefficient

ppm/C

20

Output current limit range

A

0-(+/- 5)

Output current limit accuracy

A

 .050

5 V reference output- (pin 29)

mA

1

Thermistor or RTD sensing current

                                        Low

uA

10

                                        Medium

uA

100

                                        High

uA

1000

 Supply voltage- V+ (pin 15)             

 V

+12

+18

                        V- (pin 20)

 V

-12

-18

                        VD+ (pin 16)

 V

 see text

+5

+18

                        VD- (pin 19)

 V

see text

-5

-18

Supply current- V+ (pin 15)

mA

100

150

                         V- (pin 20)

mA

100

150

                          VD+ (pin 16)

mA

0

see text

                         VD- (pin 19)

mA

0

see text

Module dissipation- TC7100

W

20

Pin Functions-

 (Physical pin locations are shown in Pin Layout Diagram.)

1. AD590+                   AD 590 bias terminal connection

2. LM335+                   LM135/335 bias terminal connection

3. Ground-                   Sensor ground

4. 10uA                       10uA current source

5. 100uA                     100uA current source

6. 1mA                        1 mA current source

7. Sensor in                 Temperature sensor input

8. Invert                      Programs the amplifier for negative temperature coefficient sensors                                                    when floating. (Connect to ground for AD590, LM135/335 and RTD. Leave                                            floating for thermistors.)

 9. Select               Programs the amplifier for current input when grounded. (Connect to ground                                         when using AD590 sensors. Leave floating for thermistor, RTD and LM135/335.)

10. Setpoint          Sets the operating temperature point.

11. Current limit      Limits the maximum output current.

12. Power driver input  Input to the power driver stage. Connect to control output for normal                                                operation.

13. Control output  Output of the temperature control loop. Connect to the power driver input or to                                    an external transconductance amplifier.

14. Ground-           Power supply

15. V+                   Power supply  (+12 to +18 V)

16. VD+                 Positive power supply for the power output stage.

17. Output+         Positive drive connection. Connect to + terminal on TE's (thermoelectric devices)                                  and to resistive heaters.

18. Output-            Negative drive connection. Connect to - terminal on TE's and to grounded side                                     of resistive heaters. This pin is internally tied to ground.

19. VD-                    Negative power supply for the power output stage.

20. V-                     Power supply (-12 to -18 V)

21. Ground-           Power supply

22. P1                   Proportional term output. Connect to pin 23 (P2) for normal operation. See text                                   for changing proportional term

23. P2                   Proportional term adjusting input

24. P3                   Proportional term adjusting input

25. I1                    Integral term output. Connect to pin 26 (I2) for normal operation. See text for                                     changing integral term.

26. I2                     Integral term adjusting input.

27. I3                   Integral term adjusting input.

28. Temp. out        Buffered sensor output. The voltage on this pin will be 10mV/uA for the AD590                                      and the same as the voltage on pin 7 (sensor in) for all other sensors.

29. 5V ref.            5 Volt /1 mA precision reference output. Used to generate setpoint and current                                      limit.

Theory of Operation

The TC7100 consists of five functional blocks: precision current and voltage sources, sensor amplifier, proportional and integral loops, current limiting and power output stage.

The precision current and voltage sources are used to generate the setpoint and input signals and to power the sensors. The setpoint and limit inputs can be generated using a potentiometer from the 5 V reference or by external analog signals. This permits remote and computer controlled applications. The precision current sources are used as the current through the thermistors and RTD's. Three sources are provided: 10u A, 100uA, 1mA. This range of sources is provided so that the user has the option of selecting either high bias currents for high developed voltages across the thermistor/RTD to reduce noise effects or low bias currents for minimum self heating.

The sensor amplifier amplifies the incoming signal from the sensor. It has 2 modes of operation: voltage and current input. The thermistors, RTD's and LM135/335 all provide a voltage signal while the AD590 provides a current signal. The sensor amplifier operates in voltage mode when the select (pin 9) is floating and current mode when the select (pin 9) is tied to ground. This amplified signal is then buffered to generate the temp out (pin 28) signal and also provided to the PI loop stage. The temp out signal is the voltage on the sensor in (pin 7) for all devices except the AD590 in which case it provides a signal of 10mV/uA. Measurements can be taken at this signal line without effecting the operation of the module. Measurements should not be taken at the sensor in or current source (pins 1,2,4,5,6,7,8,9) as significant degradation of performance will occur.

The proportional and integral (PI) control loops generate an error signal by comparing the setpoint and temp out signals and then applying analog PI processing. An initial PI constant is provided internally which works well in most applications. The PI constant can be changed by adding an external capacitor and resistor.

The current limiter compares the error signal to the current limit input and prevents the error signal from generating too high of a current in the power stage. When using an external amplifier, care must be taken to assure current limiting is functioning as expected.

The power output stage is the high power section of the device and uses the lower voltage VD+ and VD- (pins 16,19) to permit operation with minimum dissipation. The drive signal is provided by the PI loop via the control output and power driver input (pins 13,12).

Operation

 V+, V-, VD+, and VD- (pins 15,16,19,20) must be connected to the appropriate power supplies. A good quality supply with regulation is recommended. Switching type power supplies generate high frequency noise which may degrade the noise performance of the complete system but should not effect the temperature control ability. The module case is electrically isolated from the module ground (pins 3,14,18,21). The output- (pin 11A,12) is tied internally to ground. It may be necessary to use floating power supplies if a different potential in the system is used as earth ground. The VD+ and VD- voltages must be chosen with power dissipation in the module kept in mind. Typically, 2 volts over the compliance voltage required (output voltage) will yield good performance and low dissipation. Since the controller is an analog circuit, the voltage difference between the VD+ or VD- (pin 16,19) and the cooler or heater voltage is dissipated in the module. The dissipation is:

Power = Voltage difference x Current

The power dissipation must be kept below 3 watts for a module without a heat sink and 20W/12W for the TC7100/TC7100S respectively. The case temperature must be kept below 50C.

 Voltages must be provided to the setpoint and current limit(pins 10,11). A very stable 5 volt reference (pin 29) capable of supplying 1 ma is provided for generating these signals when using potentiometers or resistive dividers. (see Fig. 1) Best performance is obtained using 20 Kohm high quality 10 turn potentiometers or a 20 Kohm resistive divider. Alternatively, analog voltages from D/A converters or other sources can be used for the setpoint. The current limit should always be generated with a potentiometer or resistors as shown in Fig. 1. This provides the best protection in the event of a failure in other user supplied circuits. The output current limit is related to the voltage at current limit (pin 11) by:

Maximum output current (Amperes) = Voltage at current limit (Volts)

The PI loop compares the signal being returned from the sensor to the setpoint and adjusts the drive to the output stage accordingly. The module will increase the current to the cooler/heater until the desired setpoint or current limit is reached.

The module starts controlling the temperature as soon as power is applied. The output to the cooler/heater can be disabled by opening a switch between control output and power driver input (pins 13,12).

Specific sensor configurations are addressed later in this document.

Adjusting Proportional and Integral Loop Terms

Initial P and I constants are provided internally which work well with most small to medium thermal loads encountered in laser diode and detector cooling applications. However, these settings may have to be adjusted to optimize the performance with a particular thermal load. Initial operation should be attempted with the internal constants to determine if acceptable performance is obtained. Improper settings of P or I may result in oscillations or improper settling temperatures.

The proportional term (P) is the gain of the control loop. The internally preset gain of 30 is selected by connecting P1 and P2 (pins 22,23) together. To program a different gain, remove the connection between P1 and P2 (pins 22,23) and place a resistor between P1 and P3 (pins 22,24). The resistor value is found by the equation:

Resistor (ohms) = Gain x 1000

 The integral term (I) is the time constant of the control loop. The internally preset time constant of 0.47 seconds is selected by connecting I1 and I2 (pins 25,26) together. To program a different gain, remove the connection between I1 and I2 (pins 25,26) and place a capacitor between I1 and I3 (pins 25,27). The capacitor should be a low-leakage type, such as a polystyrene, as leakage will effect the stability performance. The capacitor value is found by the equation:

Capacitor (uF) = Time constant (seconds)

Thermistors and RTD's

The module will support thermistors and RTD's in three resistance ranges: 0 -5K, 1K -50K and 10K -500K. These ranges are based on bias currents of 10uA (0.010 mA), 100uA (0.10 mA) and 1 mA (pins 4,5,6). To choose the correct setpoint voltage for a desired temperature, the resistance of the thermistor or RTD at the desired temperature and current must be known. The resistance can be found by looking in the specification sheet for the individual thermistor or RTD. This is data supplied by the manufacturer of the device. VERE does not have a formula to calculate response curves for Thermistors and RTD junctions.  Once the resistance is known, the setpoint (pin 10) voltage for the desired temperature can be found by:

setpoint (volts) = thermistor resistance (Kohm) x bias current (mA)

When the module is running and this voltage is applied to setpoint, the module will control to the desired temperature. The voltage at setpoint should be in the range of 1 - 4 volts for lowest noise operation. High bias currents will cause self heating and effect the measured temperature. The circuit for <50K thermistors is shown in fig. 1 and the circuit for <500K thermistors is shown in fig. 2. Note that the invert (pin 8) is floating for thermistors. The circuit for RTD's is shown in fig. 3. Note that the invert (pin 8) is grounded for RTD's.

LM135 / 335

 The module will support LM135/335 IC temperature sensors. These sensors produce a voltage output and are available in several levels of accuracy. The accuracy and linearity of the output with respect to temperature can be found by looking in the specification sheet particular to the device in use. The setpoint voltage to use can be found by the following equation:

setpoint (volts) = 0.010 x desired temperature (deg C) + 2.7315

When this voltage is applied to setpoint, the module will control to the desired temperature. The circuit for the LM135/335 is shown in fig. 4. Note that the invert (pin 8) is grounded

AD590

 The module will support AD590 IC temperature sensors. These sensors produce a current output and are available in several levels of accuracy. The accuracy and linearity of the output with respect to temperature can be found by looking in the specification sheet particular to the device in use. The setpoint voltage to use can be found by the following equation:

setpoint (volts) = 0.010 x desired temp in( deg C) + 2.7315

When this voltage is applied to setpoint, the module will control to the desired temperature. The circuit for the AD590 is shown in fig.5. Note that the invert (pin 8) is grounded. 

Resistance Heating, Thermo-Electric Unipolar and Bipolar Operation

The TC7100 normally operates with a bipolar output to permit heating or cooling with a TE cooler. The industry standard configuration for a TE cooler is: Cooling occurs on the load side of the TE cooler when a positive voltage is applied to the positive TE cooler terminal and the negative TE cooler terminal is grounded; Heating occurs on the load side when a negative voltage is applied to the positive TE cooler terminal and the negative terminal is grounded. When using a TE cooler to provide full load control both VD+ and VD- are used as discussed in Operation.

When using the TC7100 for heating only (resistance element or TE cooler), no VD+ is used and the VD+ (pin 16) is tied to ground. (This must be done for resistance elements because the TC7100 will attempt to cool the load if the temperature is too high by supplying current from the VD+, further heating the load and causing thermal runaway.)

When using the TC7100 for cooling only (with a TE cooler), no VD- is used and the VD- (pin 19) is tied to ground

Same as Model TC7100s (small package unit) except uses +/- 5 vdc supply voltages @ 5 amperes, instead of the standard +/- 12 vdc with 18vdc maximum. Call our Technical Support for more details.