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DS90UB941AS-Q1: Internal clock issue

Zirui Su
Expert 5340 points
Part Number: DS90UB941AS-Q1


Hi Casey,

I have a question would like to consult with you. Currently customer uses DSI clock as the 941 reference clock, but customer faces a problem that is, when the DSI controller on the SOC side does not output the clock, the FPD-LINK 3 of the 941AS cannot work normally, which means the SOC side cannot see the address of the touch IC after the 948 on the I2C bus, and cannot initialize the touch IC.

Their current solution is to use the internal clock of 941 to make the FPD-LINK3 work normally before the DSI clock on the SOC side came, so that the touch IC can be initialized normally. Does this operation have potential risks?  Could the internal clock of 941 ensure stable i2c communication? Thank you!

  • 0
    TI__Guru** 103215 points

    Hello Zirui,

    We have seen such issues could occur before if the DSI 941AS pins are left high impedance while the DSI clock is turned off from the source and the 941AS is in continuous clock mode. The mechanism is that the 941AS can recognize any noise on the clock pins as a valid clock signal which makes the link try to switch over to the external clock source to drive the link, but since the clock source isn't actually a real clock the link would fail. The issue will not occur if you switch the DSI clock mode to non-continuous by setting 0x4F[7] = 0 while the SoC clock is disabled. Then switch the clock mode back to continuous when the SoC clock becomes available by setting 0x4F[7] = 1

    Best Regards,

    Casey