400 Hot Springs Road, Carson City NV 89706 • (775) 883-0820 • Fax (775) 883-0827 • www.hytek.com • 1

HY5620TEC Controller

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Subminiature Controller forThermoelectric Coolers(Grounded Thermistor)

The HY5620 is a subminiature proportional temperaturecontroller for thermoelectric coolers (TEC). This device is in-tended for “heat or cool” fixed temperature applications wherefront panel controls and digital readouts are not required. TheHY5620 uses a thermistor bridge to precisely measure andregulate the temperature of a device affixed to a TEC. Withproper heat sinking, the power stage of this device will deliverup to +/- 2 Amperes of current to a TEC. This controller was de-signed for a grounded thermistor configuration. In addition, thedevice can be operated with dual supplies where Vs can be aslow as +3V and VDD as low as +5V.

Features: Proportional/Integral (PI) control Small size Drive current to +/–2 amps Operation to 12 volts Control above/below ambient Temperature stability of 0.01°C Single supply operation Thru-hole or surface-mount packaging option Digital Enable/Disable Control

Maximum ratings:

Rating Symbol Value Unit

Supply Voltage 1 (Voltage on Pin 8) VDD +20 Volts DC

Supply Voltage 2 (Voltage on Pin 10) V S +12 Volts DC

Current Sink (Heat and Cool Cycle) Is 2.5 Amperes

Maximum Power Dissipation PMAX 6 Watts

Operating Temperature (Case) TMAX/MIN 100/–20 °C

Storage Temperature TSTG –65 to +150 °C

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HY5620TEC Controller

• Temperature Set Resistor Rs (Pin 6 to Pin 7)The temperature set resistor for the HY5620 controls thetemperature at which the TEC will operate. When the cir-cuit has stabilized, the resistance of the thermistor willbe equal to that of the set resistor Rs. For example, if aDale 10KΩ thermistor is used as the temperature sens-ing device, a set resistor of approximately 56KΩ will setan operating temperature of –10°C. A graph of Rs vs. settemperature is shown in figure 4 when using a Dale1M1002 thermistor.

• Thermistor, RT (Pin 1 to Pin 7)The thermistor should be located in close proximity tothe device being temperature controlled by the TEC. Itshould be in good thermal contact to avoid stability prob-lems. The thermistor ground must be connected to Pin 1.

The HY5620 has been designed for a negative tem-perature coefficient (NTC) thermistor. A thermistor with apositive temperature coefficient can be used by reversingthe leads of the TEC in which case Rcc and RCH mustbe interchanged.

• Gain Set Resistor, RG (Pin 5 to Pin 6)The ratio of the gain set resistor RG to RL controls theresponse time of the servo loop. A ratio that is too largecan cause slow response and a ratio that is too smallcan cause loop instability. In most applications RG maynot be needed since a 10MΩ resistor is internal to theHY5620 and generally provides enough gain for good op-eration.

• Loop Stability Network, RL and CL

(Pin 3 to Pin 5)The RC time constant of these two components is a firstapproximation of the thermal time constant of the servoloop. The thermal time constant of the combination of thedevice being cooled, the thermistor, and the TEC can beapproximated by applying constant power to the TECand measuring the length of time it takes to reach 66%of its final temperature.

For example, if the thermal time constant was ob-served to be 5 seconds, then a 1µF capacitor and a4.7MΩ could be chosen as the loop stabilizing compo-nents. Typical values for loop compensation componentsare shown in Table 1.

Note: The values of RG, RL, and CL are generally selectedby experiment. CL should be a low leakagenonpolarized capacitor.

• Current Limit Resistors, RCH & RCC

(Pin 1 to Pin 3, and Pin 1 to Pin 2)These resistors limit the maximum current that theHY5620 can supply to the TEC when in the coolingcycle and in the heating cycle. Rcc limits the maximumcurrent for the cooling cycle and RCH limits the maxi-mum current in the heating cycle. This feature preventsdamage to the TEC during turn on. It is often desirableto limit the maximum value of heating current as muchas 30% less than the maximum cooling current. This isbecause TECs are much more efficient heating thancooling. Figure 5 shows the approximate values for Rccand RCH required to program a desired turn on current.For example, an Rcc value of 17KΩ will limit the maxi-mum cooling current to 1.5 Amperes and an RCH valueof 13.5KΩ will limit the maximum heating current to 0.5Amperes.

• VDD (Pin 8 to Pins 11 & 12) +5 < VDD < +20 VoltsThis input supplies the voltage to the internal circuitry ofthe HY5620. The maximum current drain at this terminalis 5mA.

• Vs (Pin 10 to Pins 11 & 12) +3 < Vs < +12 VoltsThis input supplies the voltage to the HY5620 power drivecircuitry. The maximum current drain at this terminalshould not exceed 2 Amperes. Note that VDD and VS canbe driven with the same power supply in the range of +5V< VDD = VS <+12V.

Ideally VS is no more than 1.5V higher than the VMAX

of the selected TEC. Setting VS higher than this cancause excessive heating of the controller.

• Thermoelectric Cooler, TEC (Pin 9 to Pin 13)The cooling lead of the TEC should be connected to Pin13 and the heating lead should be connected to Pin 9 ofthe HY5620. If the temperature of the thermistor isgreater than the set temperature at turn on, maximumcooling current will flow into Pin 13 and out of Pin 9.Conversely, maximum heating current will flow into Pin13 and out of Pin 9 if the temperature of the thermistor isless than the set temperature at turn on. The maximumturn on current is limited by Rcc and RCH. Once the TECreaches its set temperature, the current through the TECwill decrease to exactly the value required to maintainthe correct set temperature.

Description of the HY5620 Pin Outs

• Disable (Pin 4)The TEC current can be disabled by applying a TTLhigh (+5V) to Pin 4 of the HY5620. The HY5620 is en-abled when Pin 4 is connected to ground or left open (noconnection).

400 Hot Springs Road, Carson City NV 89706 • (775) 883-0820 • Fax (775) 883-0827 • www.hytek.com • 3

HY5620TEC Controller

Figure 2 illustrates the characteristics ofthe HY5620 power drive section. It alsoillustrates the unsafe operating areawhere the power dissipated in the deviceexceeds the maximum 6 Watt rating.This curve applies for both heating andcooling operation.

Note that the resistance of the powerdrive section is approximately one ohmwhen the HY5620 is fully turned on.

Figure 3 illustrates the locus of operatingcurrent and voltage for two different TECs.

Example 1:A supply voltage of 5 Volts was chosen foruse with the ITI Ferro Tek Model6300/018/018A TEC. This device is rated fora maximum current of 1.8 Amperes at amaximum allowable voltage of 2.7 Volts.This is a load resistance of approximately1.5 ohms. The intersection of the 1.5 ohmload line and the HY5620 current sourcecharacteristics defines the locus of operationvoltage and current for both the HY5620and the TEC. In this application the currentwas limited to 1.8 Amperes when cooling andto 0.6 Amperes when heating by properselection of RCC and RCH.

Example 2:A supply voltage of 12 Volts was chosen forthe Melcor FC 0.45-66-05 TEC. This devicehas a maximum rated voltage of 7.98 Voltsat a current of 0.8 Amperes. A load line forthis device is also shown on the plot. Onceagain maximum turn on current is set byproper selection of RCC and RCH.

Note that the power dissipated in the HY5620never exceeds the 6 Watt maximumpower dissipation in both of these examples.

4 • 400 Hot Springs Road, Carson City NV 89706 • (775) 883-0820 • Fax (775) 883-0827 • www.hytek.com

HY5620TEC Controller

Figure 4

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Figure 5

NOTES:

1. Make certain the heat sink to whichthe HY5620 is mounted is flat andclean, otherwise the ceramicsubstrate may break.

2. Use a thermal compound such asDow Corning 340 between theHY5620 and the heat sink for goodthermal conduction.

3. Note that the Pin 1 identifier is shownin a bottom view. From a top view, Pinnumbers ascend in clockwisefashion.

Specifications subject to change withoutnotice.