Literature

Key Features: • Input Voltage +7 to +12 Volts Max. • Output current is 1.5A Maximum. • Assy # EVB2805 • 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. • Adjust R4 for Temperature setting • 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. 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. 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 N-Channel 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.

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