• State Resolved
  • Locked Locked
  • Replies 2 replies
  • Subscribers 62 subscribers
  • Views 1655 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.

TLV1117 noise

Shaun Wigger
Intellectual 315 points
Other Parts Discussed in Thread: TLV1117

Normal 0 false false false EN-US X-NONE X-NONE MicrosoftInternetExplorer4

Hi everyone,

We found that ~50% of boards showed significant noise on a 3.3V supply. The signature of the noise had a consistent frequency of ~400kHz but the amplitude varied from board to board.


I have included a portion of our schematic. We have confirmed that the noise is still present on the board even when we have stripped it down to just the power supply and PIC circuitry - removed Ethernet, op-amps, and wireless circuitry (present on the rest of the schematic).


The product uses an off the shelf 5V DC regulated supply. Further experimentation, using a variable output bench top power supply, showed that the amplitude of the noise changed as the input voltage decreased/increased. It seems that once the input voltage exceeded 5.1V the noise went away – although this varied from board to board that I tested. In some cases the noise didn’t go away until the input voltage exceeded 6V.


The problem has been resolved by swapping the 3.3V LDO (TLV1117) with one from Diodes Inc (ZLDO1117). Using the ZLDO1117 shows no noise on the 3.3V output.


Any ideas???


  • 0
    TI__Guru*** 143096 points

    Hello Shaun

    Here is text from the data sheet about capacitance...
    The TLV1117 is designed to be stable with tantalum and aluminum electrolytic output capacitors having an ESR between 0.2Ω and 10 Ω.
    All characteristics are measured with a 10-mF capacitor across the input and a 10-mF capacitor across the output.
    Output capacitor selection is critical for regulator stability. Larger COUT values benefit the regulator by improving transient response and loop stability.

    Is your output capacitor ceramic? (They have an ESR less than 0.2 ohms)
    If so, a small series resistor with the capacitor will stop oscillation.

    If you use the ZLDO117 without a resistor be sure to test stabilty using a load transient test at low and high temperature to ensure the design is stable.

    Regards,
    Ron Michallick