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TPS61085 won't go to zero volts

Patrick DeLuca
Prodigy 10 points
Other Parts Discussed in Thread: TPS61085

I set up the TPS61085 to have the following parameters:

Enable pin controlled by microcontroller (either 0 volts or 5volts)

8V output from a 3V source (power supply at the moment)

650Khz FREQ, 13k/3.3nF COMP circuit

 

My problem is I get 8 Volts when the microcontroller output pin is high, but I get 2.9 Volts when the microcontroller pin is grounded.  I have verified the Enable pin is grounded.  Any suggestions?  I also verified the schematic is similar to the schematic from the Evaluation Kit (TPS61085EVM)

  • 0
    TI__Guru*** 149695 points

    This boost converter uses a diode for the rectifying switch so when the converter is off the input voltage is connected to the output through the inductor and diode.  If you want input to output isolation, you will need to either add a FET in series with either the input or the output that turns off when EN is low OR move to a boost converter that uses a FET for the rectifying switch (a synchronous boost converter).

  • 0 in reply to Jeff F
    TI__Guru 61075 points

    Hello Patrick,

    Have a look in the datasheet on page 15. You will find a load disconnect circuit with a bipolar transistor. The small feature in this diagram is that the Enable pin is connected to Vin. It should be connected to your microcontroller. If now you disable the device, the output voltage will go low and at the moment when the output voltage falls below Vin + 0.7V (roughly) the transistor will turn off and disconnect the output from the input.

    Best regards,
    Brigitte