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Touch Issue when L138 EVM is operated with Battery

1258021
Genius 5120 points
Other Parts Discussed in Thread: OMAP-L138, TPS65070, OMAPL138

Hi,

We did some changes to the existing EVM to be operated from a 3.7V 3500mAh Li-Ion battery.

When we execute Touch Level Zero code from CCS what we had observed is Pressure value always shows a value of 0x3FF.

Because of that it doesn't enter into if condition which checks for the TOUCH_HOLD_LIMIT value.

Please suggest what could be the possible reason for this?

Regards,

GSR

  • 0
    TI__Intellectual 880 points

    Hello GSR,

                     Please check the TSC (Touch Screen Controller ) ADC voltage reference. Please send the circuit diagram. Which PMIC you are using.

     

    Regards

    Abhijit

  • 0 in reply to Abhijit Das84416
    Genius 5120 points

    Hi Abhijit Das,

    Thank You for the reply.

    One of our HW engineers suggested to enable VREF Bit:[B4] in ADCCONFIG register.

    Looks after enabling that bit touch is working. Can we enable this manually irrespective of whether the system is operating on AC/USB or Battery Power?

    Regards,

    GSR

  • 0 in reply to 1258021
    TI__Intellectual 880 points

    Hello GSR,

                        The touch screen is configured (enable VREF Bit:[B4] in ADCCONFIG register ) using I2C bus. You can't enable this manually without I2C bus. Please go through the datasheets of your PMIC. Are you using TMS 65070.

                        Can you explain your requirement elaborately.

     

    Regards

    Abhijit

     

  • 0 in reply to Abhijit Das84416
    Genius 5120 points

    Hi Abhijit,

    I understand that I2C interface is required to access the TPS65070. We are using TI's WinCE BSP for OMAP-L138.

    Touch panel works when it is powered either from USB or from AC. But, when OMAP-L138 is powered from battery the touch ADRESULT_1 and ADRESULT_2 shows a value of 0x3FF always.

    One task from my side is pending I will let you know the VREF value before end of the day.

    But, my question is do we have to enable Vref enable bit in ADCONFIG register when the system is powered from AC. USB or battert?

    Why I am asking this question is when the system is powered from AC or USB we are not enabling this bit manually.

    Regards,

    GSR

  • 0 in reply to 1258021
    TI__Intellectual 880 points

    Hello GSR,

                        After enableing VREF Bit:[B4] in ADCCONFIG register stiil not working Touch Screen with 3.7V 3500mAh Li-Ion battery? Please measure the ADC Ref out value        

                        when powered from USB or from AC & Also with Battery. ADC Reference voltage output on pin BYPASSshould be 2.260V in both cases (USB or from AC / Battery).


                        Check  2.2μF bypass cap from pin 40 to GND is connected. The pin is connected to an internal LDO providing the power for the touch screen controller (TSREF).

                        Are you using the Figure 49. Powering OMAP-L138  on TPS65070 datasheet. Please follow the TI recomended circuit. Please send the Schematics (PMIC &

                        OMAPL138 interface only)  ASAP it is help to Debug easy.

     

    Regards

    Abhijit

  • 0 in reply to Abhijit Das84416
    TI__Intellectual 880 points

    Hello GSR,

                        Any Update ? What is Reference voltage output on pin BYPASS ?

    Regards

    Abhijit