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Does the VCCAD and VSSAD essential to be connect to 3.3v?

yong zhang2
Expert 1305 points
Other Parts Discussed in Thread: TMS570LS3137

Hi,

I'm design a new board for my application, I've just used the enthernet, can bus and some of the GIO functions, is the VCCAD and VSSAD essential to be connected to the 3.3v supply? or can be left float?

When I design the first board, the power supply is just VCC,VCCIO and VSS. The VCCP is left float and the JTag cannot be connected with the PC through the JLink emulator. Now I need to connect the VCCP to 3.3v in the second design. And I want to make sure are there any power pin I need to connect?

The MCU is TMS570LS3137 PGE.

Thanks!

yong 

  • 0
    TI__Intellectual 845 points

    Hi yong,

    VCCAD and VSSAD can be left float.

    VCC, VCCIO, VCCP and VCCPLL must share the same GND.

    Best Regards,

    Jay

  • 0 in reply to Jay Shen
    Expert 1305 points

    Hi,Jay

    What do you mean share the same GND? Do you mean that  connect all the VSS to the same GND?

    The PGE doesn‘t have the VCCPLL pins, so it's out of consideration. 

    All the MCU power supply pins to meet my requirements are VCCIO,VCC,VCCP and VSS, is that right?

    yong

  • 0 in reply to yong zhang2
    TI__Mastermind 49120 points

    Yong,

    The VCCAD needs to be connected to the appropriate power supply if you plan to use the ADC in your application. This can be a 3.3V (nom) supply or a 5V (nom) supply.

    VSSAD also needs to be connected to the PCB ground. This is used as a ground reference for the ADC core logic.

    There are also two more pins: ADREFHI and ADREFLO. These define the high-, and the lo-reference for the ADC conversions. Typically ADREFLO is connected to ground as well, while ADREFHI is the same as VCCAD.

    Please refer to the application note: http://www.ti.com/litv/pdf/spna140 for more details.

    Regards, Sunil

  • 0 in reply to Sunil Oak
    Expert 1305 points

    Hi,Sunil

    According to what you said, If I don't plan to use the ADC module in my application, is that ok to left the VCCAD,VSSAD,ADREFHI and ADREFLO pins float? The function I need about the MCU is to implement enthernet, can bus, GIO. So, connecte the above pins or not, which is better? What's your suggestion?

    yong

  • 0 in reply to yong zhang2
    TI__Mastermind 49120 points

    Hi Yong,

    I would still suggest connecting these supply pins as specified, and then powering down the ADC in software to save power. You can leave the ADC input channels open.

    Regards, Sunil