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TPS65105 Sequence Delay

Abdul Erfan Mohammad104180
Intellectual 285 points
Other Parts Discussed in Thread: TPS65105, TPS65150

Hai,

I am using a 7" TFT LCD in my design which needs TFT bias voltages. The voltages and their values are given below. It needs a specific power ON and OFF sequence which needs to be followed for long life of the LCD. I wanted to use TPS65105 as that provides the sequence required by the LCD. But the problem I am seeing is that the voltage generation delay between the voltages is not meeting the LCD requirements that is shown in the below diagram. Is there anyway that I can increase the delay between the voltages? But I am mentioning again that sequence is meeting. Kindly help.

I have attached the LCD Power ON and OFF sequence in the attached image.

DVDD - 3.3V  - Generated by other DC-DC Regulator

AVDD - 9.6V  - Generated by Vo1 output of TPS65105

VDDG - 18V  - Generated by Vo3 output of TPS65105

VEEG - (-6V)  - Generated by Vo2 output of TPS65105

VCOM - 4V  - Generated by Vcom output of TPS65105

Regards,

Erfan

  • 0
    TI__Guru 65170 points

    Hello Erfan,

    The startup of TPS65105 is internal and the only way to get the startup of the different output voltages delayed is to use transistors in the power paths. I would recommend checking TPS65150. This part has the possibility to use delay capacitors for different startup times.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    TI__Guru 65170 points

    Hello Erfan,

    Let me clarify which output to use for which voltage to make it more clear:

    DVDD - 3.3V  - Generated by other DC-DC Regulator

    AVDD - 9.6V  - Generated by boost converter output Vs of TPS65150

    VDDG - 18V  - Generated by positive charge pump output VGH of TPS65150

    VEEG - (-6V)  - Generated by negative charge pump output VGL  of TPS65150

    VCOM - 4V  - Generated by the integrated Vcom buffer of TPS65150

    You did not mention the necessary currents but if TPS65105 can deliver enough current, TPS65150 is able to deliver enough as well.

    Best regards,
    Brigitte

  • 0 in reply to Brigitte
    Prodigy 40 points

    Brigitte,

     

    I have a very similar design with the following requirements:

    Vgh    +16.5V  @ 0.3 mA

    Vgl     -7.0V  @ 0.3 mA

    Vcom  +3.7V @ NOT Specified

    Vcc    + 3.3V  @  10 mA

    AVdd  +10.6V @ 30 mA

    What I seem to be missing on the LCD display datasheet versus the TPS65150 is Vcom and how to set it's voltage.  The LCD Display states that this pin Vcom is an input while the TPS65150 is stating that the Vcom is an input also.  So I'm currently unclear as how this is supposed to be applied.  Could you proviode some clearification as to the general intent of these pins?  If the TPS65150 does generate the Vcom Voltage, how do you set this voltage?

     

    Thanks,

    Scott

  • 0 in reply to Scott Fowler
    TI__Guru 65170 points

    Hello Scott,

    First of all, TPS65150 is able to deliver the above currents.

    VCOM pin of the TPS65150 is an output of a buffer. So you apply a voltage to the pin IN of the TPS65150 and then there is the same voltage available on the VCOM output with a higher current capability.

    The VCOM is used as the common backplane voltage of a LCD panel's pixels. Please check out http://en.wikipedia.org/wiki/Thin_film_transistor_liquid_crystal_display for more details on the panel functionality. On the front side of the panel, the TFTs are placed and the pixel needs on the back side a voltage attached that current can flow and this is VCOM.

    Best regards,
    Brigitte