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LM1085: Output Voltage greater than 3.3V

Part Number: LM1085

Hi TI,

I am using the fixed 3.3V output LM1085 LDO. When my design is powered on but not operating, the LDO has 1.1mA of current and about 2.4V output voltage. The input voltage is around 3.43V. When I begin operating the design my multimeter is reading 16.6mA of output current and an output voltage of about 5.6V. The input voltage at that point is about 5V. I have a 1000uF input capacitor and as well as a 1000uF output capacitor that is near the LDO. I am using the LDO as a power supply that is attached with jumper wires to the actual device. On the actual device I have 2 additional 1000uF capacitors a 4700uF capacitor. I confirmed the voltage readings both from the oscilloscope and the multimeter. I am wanting to figure out why I am not able to achieve a fixed 3.3V output. The 5.6V output during operation may be too high for some of the components on my board. 

I attached a picture of the LDO circuit. The LEDs and light blue potentiometers in the background are not part of the circuit and are not connected.

Regards,

Anthony Lodi

  • Hi Anthony, 

    --I am using the fixed 3.3V output LM1085 LDO. When my design is powered on but not operating, the LDO has 1.1mA of current and about 2.4V output voltage. The input voltage is around 3.43V. 

    Since you are using the fixed 3.3V, once you have a 3.43V Vin and even at no-load condition, the output should be around 3.3V. You will need to make sure the LDO is working correctly before adding the excessive additional input/output capacitors specifically for your application. 

    Regards, 
    Jason Song