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BUF12840

toshi-e2e
Genius 4790 points
Other Parts Discussed in Thread: BUF12840, BUF18830

Hi! all,

My customer plans to use BUF12840 as LDC gamma buffer.
And OUT6 is planned to use as VCOM. They want to add large capacitor for stabilizing its output level as below. 

Is there any problem about their design?

There are some evaluation data when Vs is ON and OFFf.

C=10uF:

C=60uF:

Regards,
Toshi

  • 0
    TI__Genius 14825 points

    Toshi,

    The attached presentation discusses BUF cap load drive a bit.  I believe the BUF18830 is similar in design to the BUF12840 so the content in here should be applicable, but that's just an assumption, not a guarantee.

    Gamma Buffers and Cap Loads.ppt

    I hope this helps.

  • 0 in reply to Jason Bridgmon
    Genius 4790 points

    Jason-san,
    Thanks for providing the detail explanation material.
     I understood.

    For evaluating their solution, could you provide TINA simulation models, like Tran.tsc, Tran Riso.tsc, Loop Gain.tsc, Loop Gain rsio.tsc,
    because there are not hyper links in your power point file.

    Anyway, I have an additional question.

    How do you think about the peak current of Iout6 when the buffer of BUF12840 turns on and off.
    Is it acceptable?

    Thanks and regards,
    Toshi   

  • 0 in reply to toshi-e2e
    TI__Genius 14825 points

    Toshi,

    Please find the tina simulation files attached.

    BUF_Transient_TSCs.zip

    I'm not sure I understand your second question - what do you mean "Is it acceptable?"  I think that is a question for the customer - or are you asking for confirmation that those currents are what we expect?

  • 0 in reply to Jason Bridgmon
    Genius 4790 points
    Jason-san,
    Thanks for TINA simulation models. I will try to evaluate them later.
    Anyway, what do you think about those current which customer measured?

    Thanks and Regards,
    Toshi
  • 0 in reply to toshi-e2e
    TI__Genius 14825 points
    Toshi,

    I'm still not clear what you want me to say about the currents the customer measured. Are you asking me if they are what we expect?
  • 0 in reply to Jason Bridgmon
    Genius 4790 points
    Jason-san,
    Yes,
    In case of C=10uF,
    it's flowing 83 mA momentarily at the time of power supply on. At the time of power supply off, it's -5mA.
    Incase of C=60uF,
    it's flowing 112mA momentarily at the time of power supply on. At the time of power supply off, it's -16mA.
    Is there a possibility that this measured current influences destruction in a device?

    When Vs is off, Vs keeps to higher level than Vout6. Is a Schottky diode needed between Vs and OUT6?

    Thanks and Regards,
    Toshi
  • 0 in reply to toshi-e2e
    TI__Genius 14825 points
    Toshi,

    With regards to the Supply Input Terminals, SCL, SDA, A0, BKSEL, EA0, EA1, EN, and LD, the maximum current is ±10mA.

    For the output voltage of channels 1-12, figure 1 on page 5 of the data sheet shows the output voltage swing from 0ma to 125mA output current, and page 22 of the data sheet says the the BUF12840 output stages can safely source and sink the current levels indicated in figure 1. I do not believe damage will come of this.

    One thing to know is on page 7 of the data sheet, the digital supply must be applied first before the analog supply to avoid excessive current and power consumption and possibly damage to the device. Be sure that the digital supply is present before the analog supply and you should avoid this potential problem.

    Regarding output protection, page 22 of the data sheet describes the levels of voltage on the power supplies and output pins to maintain to avoid damage. Basically, damage can occur if the output > (Vs + 0.5V)