• State
  • Locked Locked
  • Replies 6 replies
  • Subscribers 23 subscribers
  • Views 865 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.

LP2951-50-Q1 output capacitor

Atsushi Yamauchi
Genius 4810 points
Other Parts Discussed in Thread: LP2951

I would like to conifrm the output capacitor for LP2951-50-Q1.

1. I attached the file for the circuit.

    I think the output capacitor is OK, but  I'm afraid the use of low ESR capacitor for bypass capacitor

    of other (connecting) IC. Are there any problem of this circuit?

0412.2337.LP2951_circuit.pdf

2. The output capacitor requirement are >3.3uF and the ESR 30mohm - 5 ohm. Is this correct?

    Are there upper value of the capacitance (ex. 100uF, 330uF and so on)?

3.  If you can, could you provide the first pole and second pole frequency (P1 and P2 of the file I attached) ?

    3125.4555.gain-phase.pdf

Best regards,

Atsushi Yamauchi

  • 0
    TI__Guru*** 140136 points

    Atsushi-san,

    I have data for a 10uF ceramic capacitor. With and without a 330pF capacitor from VOUT to feedback pin.
    I do not have data for 100uF with a low zero frequency.

    LP2951-50 Bode.xls
  • 0 in reply to Ron Michallick
    Genius 4810 points

    Dear Ronald-san,

    Thank you for your response.

    I will use your data for the support of the customer.

    And I have a question.

    The customer use LP2951-50-Q1 in the below condition.

    Vin: 12V
    Load variation: 5mA --> 55mA, 55mA --> 5mA
    Ambiant temperature: -20 to 80 degreeC

    In this case, is LP2951-50-Q1 stable in this condition?
    And how much is the time (rise and fall time) LP2951-50-Q1 can allow?

    Best regards,
    Atsushi Yamauchi

  • 0 in reply to Atsushi Yamauchi
    TI__Guru*** 140136 points

    Atsushi-san,

    Load steps are OK. Note that there are load transient tests wave forms in data sheet.

    Note the voltage increase at "instantaneous" load reduction. It takes couple micro seconds to reduce the current flow. 

  • 0 in reply to Ron Michallick
    Genius 4810 points

    Dear Ron-san,

    Thank you for your reply.

    I have questions for LOAD TRANSIENT RESPONSE in the datasheet page 9.

    1. How much is rise and fall time of load current for these figure?

    2. In the fall period of load current, load voltage increases. I understand it. But I don't know load voltage has slope in

        the fall period of load voltage. Does LP2951-50-Q1 control this voltage? I think the shape is similar it increasing

        load current.

    3. In the case rise and fall time is a few micro seconds, the peak is reduced.

        In this case, is the peak voltage  smaller than 5.1V? 

        In the specification, the load regulation is 0.3% max. How much is the rise and fall time for this specification?

    Best regards,

    Atsushi Yamauchi

  • 0 in reply to Atsushi Yamauchi
    TI__Guru*** 140136 points

    Atsushi-san,

    1) 1uS or less.
    2) The voltage fall is based on load current and output capacitance. This is the capacitor 'over charge' drain time.
    3) Slower edge on load will be helpful. I don't know how much. Data sheet load regulation is a DC voltage change for a DC load change (same as very slow change). 

  • 0 in reply to Ron Michallick
    Genius 4810 points

    Dear Ron-san,

    I have a quetsion.

    In the datasheet page9, what is the condition? 

    Is CL the capacitive load? How much is the output capacitor?

    Best regards,

    Atsushi Yamauchi