• Resolved

TPS65150: White Halo on LCD Display

Prodigy 30 points

Replies: 4

Views: 47

Part Number: TPS65150

Hi, 

I am using TPS65150RGER as the Display Driver for providing the below voltages and Power ON Sequence. 

  • I am observing White Border on the LCD Display randomly sometimes which goes away once the display is ON for 10-15 minutes. The measured voltages are AVDD = 9.6V, VGH = 17.36V, VGL = -6.02V, VCOM = 3.09V. 
  • I intend to shut down the below voltages when the display is off so as to avoid draining the battery while the System is in Shutdown state. Currently, in my design, I have connected the battery to the VIn directly. Therefore, even when my display is off, the IC is drawing around 100mA continuously. 

Can you kindly check the attached schematics and suggest me a way to avoid the above two problems.

Any suggestions would be helpful.

 

1. AVDD

2. VGH

3. VGL

4. VCOM

5. Superimposed Sequence

  • Hi Surender,

    Thanks for your question. Let me contact the expert for this part. You can expect a response by 2/14/20.

    Best,

    Grant

  • Hi Surender,

    I reviewed your schematics and it mostly looks good. Since your desired VCOM voltage is 3.2V, the only modification I would recommend to schematics is to increase R71 slightly to yield this 3.2V from the resistor divider. Also based on the VBAT level, please ensure that you are using a proper compensation network from table 1 in the datasheet. Current network you are using is for VBAT=3.3V so no change needed if that is indeed the voltage level of your VBAT supply input.

    As for white border on the display, this could be related to some issue with the display itself or the timing of the data for the display. To isolate whether  this is a problem with the  bias supply rails or the display/data timing, you will need to monitor AVDD, VGH and VGL rails on the scope to see if you observe any difference between first 15 minutes of operation and later. Based on this observation, further debug needs top happen. If there is nothing wrong with the power rails, you will need to focus debug on the display/data timing.

    TPS65150 will continue to power the output rails as long as the input supply is above under voltage lockout (UVLO) level. If you want to power down the rails, you will need to use an external mechanism such as a power switch that is controlled by an external signal to remove Vin to TPS65150. Unfortunately, I don't see a more seamless solution.

    Kind Regards,

    Liaqat

  • In reply to Liaqat Khan:

    Hi Liaqat,

    Thank you for your reply. I will try to implement the changes you have suggested.

    In my design, the VBAT nominal voltage is 3.7V and varies between 3.2V to 4.2V. Can you kindly suggest a suitable compensation resistor and capacitor.

    Best Regards,

    Surender

  • In reply to Surender Reddy S:

    Hi Surender,

    For the VBAT range you mentioned, what you currently have (470pF, 33k) should work well.

    Kind Regards,

    Liaqat