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LT 3033 malfunctioning

Hello,

I am trying to test the IC : LT 3033. It has a linear regulator with a internal reference voltage of 0.2V. I had set feedback resistors of 150K and 11k to expect an output of 2.9V approx. However I am getting an output voltage of 0.48V at a supply of 4.5V. Also the output voltage is increasing with increase in input voltage. I am attaching the datasheet and a zip file of board and schematic files that I have created in Autodesk eagle 9.1.

lt3033.zipPDF

  • There are no input/output capacitors in your schematic. The minimum output capacitor is 10uF for LT3033, and a 10uF cap is needed at the input. Remove C2 that is in parallel with the bottom feedback resistor to keep the system stable.

  • Yes I have not shown them in the schematic, however on the PCB I have connected capacitors between input and ground and output and ground. Also I haven't connected the capacitor in parallel to the bottom feedback resistor. I have left that open ie there is no capacitor in parallel to the lower feedback capacitor. Still the system fails to give desired output.

  • Are the capacitors placed close to the IC? What's the load current?

  • Hello

    The IC is working now. I had messed up the values of the capacitors.

  • Hello

    What happens in thermal shutdown and overcurrent shutdown of the IC? I have connected an inductive load at the output and when the current increases beyond a certain value the output voltage starts switching between 0 and the set voltage. However since the load is inductive the current should remain constant, with some ripple because the voltage is not constant. But what is being observed is totally different. The current passing through the inductor drops sharply to 0 when the output voltage of the IC becomes 0 (due to shutdown). So I want to know what exactly happens in a thermal shutdown and overcurrent shutdown.

    The first waveform is current through the inductor. The second waveform is the voltage at the output of the IC.

    The output voltage is increased by changing the value of the resistor divider resistors. Input voltage is 4.2V, current is limited to max of 1A, Inductor = 2.6mH, series resistance = 1.2 Ω, input capacitance = 100uf and output capacitance = 100uf

  • Please contact ADI support in your area who can look at your applications. This LDO may not be suitable for requirement of your inductive load.