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PLL_VIDEO1 and PLL_VIDEO0

Michi Yama
Guru 10030 points
Other Parts Discussed in Thread: AM3874

Hi,

I have two questions regarding PLL_VIDEO.

According to AM3874 datasheet, PLL_VIDEO0 is used for HDVPSS SD VENC, and PLL_VIDEO1 is used for HDVPSS VOUT0.

Now my customer uses only VOUT0 signal.  So my customer cut "VDDA_VID0PLL_1P8" power supply to PLL_VIDEO0. In this condition, if he power of the sytem is turned on, HDVPSS VOUT0 output is not done.  If VDDA_VID0_PLL1P8 is supplied o the PLL_VIDEO0, HDVPSS VOUT0 signal  is output correctly. After boot up, if PLL_VIDEO0's power supply is cutt off, system works correctly.

1) PLL_VIDEO1 is for HDVPSS VOUT0,  PLL_VIDEO0 is for HDVPSS SD VENC. This is correct?

2)  Why HDVPSS VOUT0 is not output if the VDDA_VID0PLL_1P8 is not supplied to PLL_VIDEO0?

Please advise me.

 Best regards,

Michi

  • 0
    TI__Guru**** 170625 points

    Hi Michi,

    Michi Yama said:
    1) PLL_VIDEO1 is for HDVPSS VOUT0,  PLL_VIDEO0 is for HDVPSS SD VENC. This is correct?

    Yes, this is correct.

    Michi Yama said:
    2)  Why HDVPSS VOUT0 is not output if the VDDA_VID0PLL_1P8 is not supplied to PLL_VIDEO0?

    This is what we have in the AM387x datasheet:

    4.4 Handling Unused Pins
    When device signal pins are unused in the system, they can be left unconnected unless otherwise noted in the Terminal Functions tables (see Section 3.2). For unused input pins, the internal pull resistor should be enabled, or an external pull resistor should be used, to prevent floating inputs. Unless otherwise noted, all supply pins must always be connected to the correct voltage, even when their associated signal pins are unused.

    Per my understanding, VDDA_VID0PLL_1P8 is voltage supply pin. It is described in subsection 3.2.26 Supply Voltages:

    VDDA_VID0PLL_1P8 - 1.8 V Analog Power Supply for PLL_VIDEO0

    I do not see a note, saying that this pin can be left unconnected if it is unused! Thus your observation match with the description in the AM387x datasheet: Unless otherwise noted, all supply pins (in our case VDDA_VID0PLL_1P8)  must always be connected to the correct voltage, even when their associated signal pins are unused.

    BR
    Pavel