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TPS65150: TPS65150 VCOM buffer problem

William Hsieh1
Intellectual 370 points
Part Number: TPS65150

Hi 

My TPS65150 schematic is on the below.

If we don't use the VCOM buffer and derive the VCOM voltage 4V with resistor divider 165K ohm and 95.3K ohm, the 5V input supply current is normal.

If we use the VCOM buffer, the 5V input current would increase 700mA than the above condition.

We follow the design guide in the data sheet and hope for some suggestion.

Thanks! 

Wiiliam.

  • 0
    TI__Mastermind 18550 points

    Hello William,

    When you drive VCOM voltage using the 165K/95.3K, then off course almost negligible current will pass through the 165K resistor.

    It appears to me that the load on +4V_LCD_VCOM net is very high. You can verify that by disconnecting the load from +4V_LCD_VCOM node to see if the current stays normal. If the current stays normal once load is removed from this node then the issue is with the load drawing a lot of current not with TPS65150 circuit. In that case you will need to debug why there is such a heavy load on the +4V_LCD_VCOM from your display panel.

    Kind Regards,

    Liaqat

  • 0 in reply to Liaqat Khan
    Intellectual 370 points

    Hello Liaqat,

    After I change the VCOM buffer output capacitor from 1uF to 0.1uF, the 5V power consumption is normal.

    The VCOM voltage with capacitor 1uF is unstable and the voltage peak to peak is about 2V,and e voltage peak to peak is just about 80mV with capacitor 0.1uF.

    So I guess that there must be VCOM bypass capacitor inside the LCM panel and the VCOM charging capability of TPS65150 results in this problem.

    Is any total capacitor limitation for VCOM voltage of TPS65150?

    William

  • 0 in reply to William Hsieh1
    TI__Mastermind 18550 points

    Hello William,

    VCOM output is designed to  drive typical up to 1uF capacitive loads. I also suspect that there is additional capacitance in your LCD module requiring you to reduce on board capacitance for TPS65150 VCOM output.

    Kind Regards,

    Liaqat