• State TI Thinks Resolved
  • Locked Locked
  • Replies 9 replies
  • Answers 3 answers
  • Subscribers 64 subscribers
  • Views 692 views
  • Users 0 members are here
Support feedback
Options
Options
Similar topics

This thread has been locked.

If you have a related question, please click the "Ask a related question" button in the top right corner. The newly created question will be automatically linked to this question.

TLV700: what is the feedback resistor value of TLV70033

Yangbo
Intellectual 1690 points
Part Number: TLV700

Hi Expert,

See schematic below. We put a diode between input and out to speed up output capacitor discharging during power off. However, the output voltage is not regulated at 3.3V. It goes up slowly and end up close to input voltage. Then we replace the diode with a resistor. The output voltage is nor correct when the resistor value is less than 2M ohm. Can you help to understand the reason behind this? And can you let us know the feedback resistor value inside. thanks.

regards,

Yangbo

  • 0
    TI__Mastermind 36525 points

    Hi Yangbo,

    Are you referring to a simulation or a hardware measurement?

    Can you please confirm that the diode is installed correctly?
    The fact that the output voltage ends up close to the input voltage suggests to me that the anode could be tied to Vin, and the cathode could be tied to Vout.

    The device you have in your schematic is a fixed output at 3.3V
    There is no feedback pin or adjust pin to change the setpoint.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Intellectual 1690 points

    Hi Stephen,

    Thanks for your quick response.

    hardware measurement. The diode is installed correctly.

    Yes, it is 3.3V fixed output. We want to know the feedback inside. it should have feedback resistor if you want to regulated at 3.3V.

    Regards,

    Yangbo

  • 0 in reply to Yangbo
    TI__Mastermind 36525 points

    Hi Yangbo,

    The feedback resistors are both inside the IC for this linear regulator.
    For adjustable linear regulators, you do not connect a feedback resistor from output to input.

    If this regulator was adjustable then you would connect the feedback resistor from the output to the "feedback" (FB) pin or the "adjust" (ADJ) pin.
    Some other companies have additional names for this pin.

    The following app note shows some good diagrams of the setpoint resistors, how they connect to the internal op-amp, and the basic circuitry of an LDO.

    www.ti.com/.../snva558.pdf

    The TLV700 does not require an external feedback resistor as they are all inside the IC.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Intellectual 1690 points

    Stephen,

    I just want to know the resistor value. It can't be find in the datasheet.

    thanks,

    Yangbo

  • 0 in reply to Yangbo
    TI__Mastermind 36525 points

    Hi Yangbo,

    That information is normally not released, and is typically not needed by the customer.

    There does not seem to be a need for that information based on your question.

    I do not see what is broken in the LDO design.
    If you connect a resistor from the output to the input, I would expect the results you are receiving.
    I see two different ground symbols in the schematic above - please confirm the grounds are connected in the application, and one side is not floating vs. the other side.

    You can try removing any feedback you have from the output to the input (diode, resistor, other circuitry).
    If that does not improve the LDO operation, please provide oscilloscope plots of the input voltage, enable voltage and output voltage.

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Intellectual 1690 points

    Hi Stephen,

    Normally there shouldn't be any resistor or diode between input and output. The diode here used to shorten power off time. Energy storied on output capacitor can be discharged through the diode. However, adding the diode makes output voltage regulated at a wrong value. could you help us to understand this? How does the diode impact the output voltage?

    Regards,

    Yangbo

  • 0 in reply to Yangbo
    TI__Mastermind 36525 points

    Hi Yangbo,

    If the diode is installed correctly, there should not be the effect you are describing.

    Can you share the manufacturing part number of the diode?

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Mastermind 36525 points

    Hi Yangbo,

    Another question is the temperature you are observing this behavior.
    Is this something you see at ambient temperature?

    Thanks,

    - Stephen

  • 0 in reply to Stephen Ziel
    TI__Mastermind 36525 points

    Hi Yangbo,

    Since it has been a week without a reply, we assume that this issue has been resolved.  If this is not the case, please feel free to reply.

    Thanks,

    - Stephen