LXE1810 L I N F I N I T Y Thermo Electric Cooler Drive D I V I S I O N NO T R OB EC SO OM L ME ET ND E P ED R FO OD R NE UC W T DE SIG NS KEY FEATURES • Input Voltage +7 to +12 Volts Max. • Adjust R4 for Temperature setting • Output current is 1.5A Maximum. • Assy # EVB2805 • Change the resistance value of R8 to set the maximum output voltage limit. Use a dummy load of 20 to 50 ohms while making this change. A smaller resistance value increase the output voltage minimum value is 15k ohms. • Thermister Input is not polarity sensitive for RT-1 and RT-2, connect so wires do not cross. • If the set temperature is lower than the room temperature when power is applied; the output drive will put a positive potential across the Thermo electric cooler. WWW . Microsemi .C OM DESCRIPTION IMPORTANT: For the most current data, consult MICROSEMI’s website: http://www.microsemi.com/ BOTTOM TOP R2 R4 C4 R1 C5 C2 R7 C7 C1 U2 R3 R11 U1 C8 R9 R8 R6 C6 R12 R10 C9 R5 C10 R13 Q2 C12 Q1 L2 C11 GND L1 C3 +12V TEC+ RT-1 RT-2 C13 C14 TEC- LXE1810 TEC Copyright 2000 Rev. 0.4, 2002-10-31 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 1 LXE1810 L I N F I N I T Y Thermo Electric Cooler Drive D I V I S I O N NO T R OB EC SO OM L ME ET ND E P ED R FO OD R NE UC W T DE SIG NS The LX1810 has an internal 5V reference at PIN 1. This reference is used with the POT adjustment that is the temperature setting and with the thermister resister divider that is the temperature feedback. The value of R3 is set equal to the value of the thermister at the temperature of operation, (±20%). The values for R5, R6, R7, C6, & C7 are used to set the loop compensation for stable closed loop operation. This Eval board has been compensated for a Marlow Industries Inc. MI1012T-01, TEC device. The value of R8 sets the peak output voltage limit of the power amplifier. The value shown sets the limit to 4 volts maximum. This is the method used to set the maximum current through the TEC device. With a TEC resistance of 3 ohms the maximum current will be 1.3 amps. The LX1810 has an internal cycle by cycle current limit that is activated after a count of 9 cycles of over current. When activated the LX1810 goes into a hiccup mode until it has 2 cycles of normal current. This mode will prevent damage when the output has a short circuit. The inductors, L1 and L2 are selected for the continuous current rating required by the device being driven by the power amplifier. At the 400kHz switching frequency an inductance value between 10µH and 20µH should be used. Now you can find the smallest package at the desired price. C13 and C14 provide an LC low pass filter. The TEC devices have a slow rate of change of temperature with time, which means the loop bandwidth will probably be under 100Hz. This means that the LC filters can be set in the range of 10kHz. Therefore, you can use the largest cap value with the voltage and package size required by your design. WWW . Microsemi .C OM APPLICATION NOTE The LX1810 has internal FET drivers capable of driving the highest power SO-8 package MOSFETs. An example of these devices are the Fairchild FDS6875 Dual P-Channel MOSFET, capable of 6 amps and the FDS6890A Dual NChannel MOSFET, capable of 8 amps. With these devices and the proper inductors, and the correct amount of heat sink, the power amplifier is capable of 5 amps continuous at an output voltage of 12 volts. So, any output power design is feasible up to this maximum design with the proper selection of components. APPLICATION +12V TEC - TEC- LX1810 GND RT-2 N/U ISI CP VDD PVDD P+ N+ NPPGND CN FB INFB IN+ FB OUT TEC +TEC+ APPLICATION RT-1 1 GND N/C 2.5VREF RPWM CPWM N/U N/U N/U SLEEP N/U N/U EA IN EA OUT Figure 1 – Application Schematic Copyright 2000 Rev. 0.4, 2002-10-31 Microsemi Linfinity Microelectronics Division 11861 Western Avenue, Garden Grove, CA. 92841, 714-898-8121, Fax: 714-893-2570 Page 2