Floating VDDA/VSSA?

[joeygouly]

Hi,

On my first design using an MKL27Z, I connected VDDA/VSAA directly to VDD/VSS.

It seems to work fine. However, on my next design I'd prefer to leave them floating, since I'm not using them.

Is that going to cause any issues?

Thanks,

Joey

[davidsherman]

Agreed, unless the data sheet specifically says you can leave them floating, connect them.  You may not be using the analog circuitry, but if the I/O signals still feed into the unpowered analog section internally (very likely), you could have some significant problems with excessive current because some buffer amplifier isn't powered.  Op amps in particular don't take kindly to having analog signals applied when they aren't powered.

[bobpaddock]

Never leave a power supply line float unless you know intimate details of the internal chip design or the data sheet says it is okay to do that. The section that has no power could have a lower impedance increasing power consumption as it loads down the powered up circuitry.

[kerryzhou]

Hi Joey Gouly,

    Do you want to use the analog module? If yes, you must connect the VDDA/vssa, because these pin is the power supplier for analog module, it is recommended to connect the unused supplies to their respective voltage.

Wish it helps you!

Have a great day,
Jingjing

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[joeygouly]

I don't use the ADC.. nor any other analogy module!

Another VDD related question: is it ok to have a VDD plane on the same side as the MCU? Seems like the easiest way to tie all VDD pins together. (I will upload a picture later)

Thanks!

[kerryzhou]

Hi Joey Gouly,

    If customer doesn't need to use analog module,  we still recommend customer to connect VBAT, VDDA, VREFH, VREFL, VSSA pin, avoid leave these pins floating.

VBAT pin connect with VDD; VREFH connect with VDDA connect to analog VDD; VREFL connect with VSSA connect to analog GND.

    The VDD plane  on the same side as the MCU, do you mean you Copper pour the VDD in the same side board?

Wish it helps you!

Have a great day,
Jingjing

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