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WEC7 BSP,Lcd clock can make the Touchscreen be not unstable after am3359 power on

Other Parts Discussed in Thread: AM3359

Hello, TI FAE

now i use am3359zcz and the BSP is from the TI, We use the WEC7 system.

and my products will be finished soon.but i find a problem which let me confused.

because we need to use different 7'ch 800*480 color lcd for different products. i change the lcd clock from 36MHZ to be 30MHZ in the BSP like the following pic:

Then i find the Touchscreen be not unstable after am3359 power on every time.
although i calibrate the touchscreen first time, it is ok, then i power off AM3359, and i power on am3359 again, the position is moved as i touch the same position.
i check the Touchscreen control registers and ADC ouput.  the ADC ouput is different  much at the same position after i power on the AM3359 every time.
like: first time: 10-20
second time:285-300
third time:124-130
it cause that i can not touch the right position in the touch panel after i power on the am3359.
 
then  i change the lcd clock from 30MHZ to be 36MHZ in the BSP again, the touchscreen ADC ouput is ok, the value is 20-30 at the same position every time i power on the AM3359. And the touchscreen is stable.
 
i am confused that why the LCD clock deincrease can make the touchscreen be unstable when i power on the AM3359 every time. it is not caused by power supply noise because the ADC output is moved a constant value every time. like:285-300, (real value :20-30)