• State Resolved
  • Locked Locked
  • Replies 5 replies
  • Subscribers 62 subscribers
  • Views 240 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.

LP5907: output voltage not 0 when enable on GND

Stefan Lintner
Expert 4255 points
Part Number: LP5907

HI Team,

a customer observed following behavior of LP5907UVE-3.3. Do you know why this might happen?

When pulling the enable input to GND, the output voltage of the LP5907UVE-3.3 remains on 190mV.

Thank you for your help!

BR,
Stefan

  • 0
    TI__Genius 16606 points

    Hello Stefan, 

    Would you happen to have scope shots of this event? (scope shot to include: VEN, VIN, IOUT, VOUT)

    The LP5907 has an internal 230 Ohm resistor to help discharge the output. The EN pin voltage must be lower than the VIL threshold to ensure that the device is fully disabled and the automatic output discharge is activated. 

    The 190mV output could be held there because automatic discharge is not being activated and the output capacitor is taking longer to discharge. 

    Best,

    Juliette

  • 0 in reply to Juliette
    TI__Expert 4255 points

    Hi Juliette,

    The output never seems to go below 190mV.

    Below the scope shot:
    Green --- VIN, Yellow --- EN, Blue --- VOUT

  • 0 in reply to Stefan Lintner
    TI__Genius 16606 points

    Hi Stefan, 

    Are you pulling a current on this device?

    Where are you measuring the Output voltage from?

    I am thinking that this may be parasitic/stay capacitance on the PCB but will have to confirm with some colleagues before giving a definitive answer. 

    Best,

    Juliette

  • 0 in reply to Juliette
    TI__Expert 4255 points

    Hi Juliette,

    unfortunately the output of the LDO goes directly into an inner layer of the PCB, so it cannot be measured if there is actually current being pulled right now.

    The weird thing is that this issue did not show up when another LDO was used.

    Any ideas?

    BR,
    Stefan

  • 0 in reply to Stefan Lintner
    TI__Genius 16606 points

    Hi Stefan, 

    We had someone check this issue out on the benchtop and they believe you have leakage underneath the IC allowing Vin to slightly power Vout through the leakage. 

    Please confirm that your board is very clean and free from flux residue.

    these are the scope shots from the EVM turning off:

    Please note how the output decreases sharply in these scope shots, versus yours - leading us to believe it's leakage current.

    Best,

    Juliette