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TLV1117 output issue

leroy wu
Prodigy 20 points
Other Parts Discussed in Thread: TLV1117, LMZ12002

Design circuit:

output :

  • 0
    Guru 140200 points
    Hi Ieroy,

    what is supplying the inputs of regulators? A DC/DC-switcher? Can you show us a scope plot of the input signals?

    Kai
  • 0 in reply to kai klaas69
    TI__Mastermind 23361 points
    Hi Leroy,

    In order to better assist you, will you also include Vin in the waveform? Please provide the resistors values for the resistor divider pair.

    Regards,
    Jason Song
  • 0 in reply to Jason Song
    Prodigy 20 points

    Vin circuit

    Vin / 3.3V / 1.8V :

    and I used IC type :

    TLV1117-18IDCY (T5)

    TLV1117-33IDCY(TV)

    The ADJ/GND pin Connect to GND ~ it OK?

  • 0 in reply to leroy wu
    Guru 140200 points
    Hi Leroy,

    yes, connecting the ADJ/GND pin to GND is correct for the TLV1117 with fixed output voltage.

    I see two issues:

    1. The TLV1117 needs an output cap with an ESR between 0.2R and 10R to work stably. This is easiest achieved with an aluminium electrolytic. The ESR of a ceramic cap might be too small.

    2. I think the input ripple form the DC/DC-switcher is punching through the TLV1117 because of insufficient power supply rejection ratio (PSRR) of TLV1117 at the high switching frequency. So, I would recommend the introduce of a filter between the LMZ12002 and the TLV1117. Put a 10...22µH high current choke in front of the input cap of TLV1117. If you notice ringing add some series resistance to the choke.
    Even a simple high current ferrite bead could be sufficient as filter.

    What is your load current?

    Kai
  • 0 in reply to kai klaas69
    TI__Mastermind 23361 points
    Hi Leroy,

    Can you help to identify what are the yellow, red and blue in your scopshot?

    Regards,
    Jason Song