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LP2966: The rising voltage of the power supply exceeds the specified value.

Hayashi
Expert 1840 points
Part Number: LP2966

Hi team,

When my customer power on system, the LP2966 output a voltage higher than the set voltage only 1ch.
The power supply configuration of the customer is as follows.

Input :5V(Several milliseconds to get up)
Output1:1.8V　(Up to 2.4V as well as 3.3V output. Then it drops to 1.8V.)
Output2:3.3V

Perhaps I think that it is the specification of the reference voltage on the input side.

Please let me know if you have any ideas?

Best regards
Hayashi

  • 0
    TI__Prodigy 515 points
    Hello Hayashi:
    Do you know what the part # customer ordered? The part number has the output voltage information. for example, LP2966IMM-1833/NOPB, the four digitals after "-" indicate ch1 output 1.8V, ch2 output 3.3V.
    Would you provide a scope shot of Ch1 startup with Vin, Vout, and SD pins, and the timing sequence of SD1 and SD2?
    Regards,
    Min
  • 0 in reply to Min Hudgins
    Expert 1840 points

    LP2966IMM-1833.pdfMin san

    I am sorry to delay to reply.

    I answer your question.

    # customer ordered

    LP2966IMM-1833/NOPB

    Both of SD1 and SD2 is connected to Vin.

    The breakdown of the attached file is explained , yellow:Vin, blue:
    output 3.3V, pink:output 1.8V. (Please ignore the bottom.)

    The input capacitor is 4.7uF and the output capacitor is 10uF.

    It would be greatly appreciated if you could explain the details.

    Best regards

    Hayashi

  • 0 in reply to Hayashi
    TI__Prodigy 515 points
    Hi, Hayashi:
    It took a few microsecond for LDO control loop to response when the channel 1 first reached its 1.8V nominal value. At the meantime, the LDO was still charging the output cap, and the output voltage continued to rise(overshoot). With your setup, channel 1 output rose to 2.4V. It exceeded the 1.8V nominal, and the control loop tried to regulate it back to the nominal value. But for the channel 2, the output voltage was still below the nominal 3.3V. By the time channel 2 reached its nominal, the control loop was fully responsive to regulate to its nominal value.
    Regards,
    Min