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DM816x Analog Dac usage - VDAC_VREF pin query

K Md Feroz Irfan
Expert 7225 points
Other Parts Discussed in Thread: TMS320DM8168

Hi Team,

I have query related to processor TMS320DM8168.
In the data sheet ,  "Table 3.2.21 Analog Video Output Signals" is given.

In that, AH19 pin is defined as VDAC_VREF and following description is given:

"Video DAC reference voltage (0.5 V). When the video DACs are powered down, this pin should be left unconnected."

In our NVR, can we leave this pin unconnected? We are using IOUTA (AT21), IOUTB (AR21), IOUTC (AP21) which are Analog HD DAC for VGA interface. But we are not using rest of Analog SD DAC.

So now, VDAC_VREF is required? VDAC_VREF is used for only SD DAC or both HD DACand SD DAC?

Can it be left unconnected?

KIndly confirm,

Thnaks & Best Regards

Feorz

  • 0
    TI__Guru**** 170625 points

    Hi Feroz,

    Check the below thread, it should give you the requested info:

    http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/717/t/109400.aspx

    Best Regards,

    Pavel

  • 0 in reply to Pavel Botev
    TI__Expert 7225 points

    Hi Pavel,

    Thanks for the inputs. However it seems like the said e2e it was pretty clear that none of the IOUTA-IOUTG are used/active.

     

    However in below case IOUTA (AT21), IOUTB (AR21), IOUTC (AP21) which are Analog HD DAC for VGA interface. But we are not using rest of Analog SD DAC.

    So now, VDAC_VREF is to be left unconnected? 

     

    Thanks.

    Best Regards,

    Feroz

     

  • 0 in reply to K Md Feroz Irfan
    TI__Guru**** 170625 points

    Feroz,

    This is what we have here:

    http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/717/t/109400.aspx

    When the video DACs are powered down, the VDAC_VREF pin should be left unconnected.

    When a specific Video DAC output [IOUTA - IOUTG] is powered down, the corresponding Analog Video Output terminal functions should be left unconnected.
    VDAC_VREF - When the video DACs are powered down, this pin should be left unconnected.
    VDAC_RBIAS_HD - When the HD DACs are powered down, this pin should be left unconnected.
    VDAC_RBIAS_SD  - When the SD DACs are powered down, this pin should be left unconnected.

    DM816x TRM:

    3.2.6.3
    Video DACs Power Down Control
    In applications in which the Video DACs are not used at all, the power supply to the Video DACs can be powered down by configuring the HD_DAC_CTRL and SD_DAC_CTRL registers of the Device Configuration Registers.

    http://e2e.ti.com/support/dsp/davinci_digital_media_processors/f/717/t/106043.aspx

    If you are not using the Video DACs and they are powered down, then you should leave this pin unconnected.  This device actually does not support RF out, so you just need to consider whether you would need to use the SD or HD-DACs (IOUTA-G).

    Per my understanding, as you are using video DACs IOUTA, IOUTB and IOUTC, you can not leave the VDAC_VREF pin unconnected. VDAC_REF is required. VDAC_VREF is used for both HD_DAC and SD_DAC. Both HD_DAC and SD_DAC are video DACs.

    Best Regards,

    Pavel