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BUF18830 - Vcom OUTPUT Amplitude

Kawai
Guru 19775 points
Other Parts Discussed in Thread: BUF18830

Hi Team,

Please allow me to ask you if BUF18830 Vcom output amplitude could be set to as low as 0.5V. I believe it can not, however, could you please give us your comment ?

Best Regards,
Kawai

  • 0
    TI__Mastermind 18780 points

    Dear Kawai,

    You can set the Vcom that low, but your load will dictate whether or not the part is usable in your application. If you reference figure 1 below from the datasheet, you will see that with Vcom set to that voltage level, the part is only capable of driving around 100mA of current. You set the Vcom values in the part utilizing the binary buffer code outlined in the datasheet.

    Please let me know if you need anything else.

    Sincerely,

    Carolus

  • 0 in reply to Carolus Andrews
    Guru 19775 points
    Hello Carolus-san,

    Thank you very much for the answer.

    Best Regards,
    Kawai
  • 0 in reply to Carolus Andrews
    Guru 19775 points

    Carolus-san,

    Could you please allow me to ask you a little more to make my understanding better ?

    Q2). I believe above Figure 1 describes maximum output current for each output voltage settings for Vcom output. Am I correct ? Or, is it showing that output voltage will depend on output current.

    Q3). What is the meaning of upper curve and lower curve in figure 1 ? 

    Q4). I can find the Vcom output voltage vs CODE graph in Figure 3. What is the Vcom output voltage equation including CODE setting ? I believe it is the following calculation, however, When I calculate, I come up with Vcom=Vs.

    Thanks in advance.

    Best Regards,

    Kawai

  • 0 in reply to Kawai
    TI__Mastermind 18780 points

    Dear Kawaii,

    A2) Yes, that is my interpretation as well. The way I understand it, you would use the CODE register to effectively program the Vcom outputs to the desired voltage based on that curve, and then that output voltage would dictate the amount of output current the device can drive with.

    A3) They are two simultaneous data points for output current on the curve. For example, you can set Vcom to either 2V or 11.5V. At either of these voltages, the part can provide an output current of around 300mA. The two graphs provide a totality of data for the 0-14V range, with the exception of ~5V- ~9V. I would assume that we do not recommend utilization of the part in this range.

    A4) The datasheet font is misleading here. None of the symbols present should represent the minus mathematical operator. They are hyphens, and these variables correspond to the data sheet. To clarify, equation 1 should read "Output X (pins 14-19, 23-28, 32-37) equals the supply voltage (pin 13, 22, or 31) times the code ratio." Equation 2 should read "Vcom output X (pin 2 or 11) equals the Vcom supply voltage (Pin 1 or 12) times the code ratio." Therefore, you should not need to substitute any values, both equations are simple ratio calculations based off of the set code. Does this make sense? Let me know if it does not click and I will try to clarify further. Hope this helps.

    Sincerely,

    Carolus

  • 0 in reply to Carolus Andrews
    Guru 19775 points
    Hello Carolus-san,

    I apologize for my delay. Thank you very much for your explanation.

    Just my note to clarify the equation.

    OUTx = Vs x (CODE / 1024)

    Vcom_outx = Vs _vcom x (CODE / 1024)

    Best Regards,
    Kawai