Can VDDA VREF+ and VssA connect to VSS(ground)?

[Deviprasad Bokkisam]

I am using STM32H735,TFBGA-100 controller with 550MHz.I don't need ADC and DAC functions.

1.Shall i connect VDDA,VREF+ and VssA to ground(Vss)? if yes, what is the recommended(through any resistor or  shorted)way to connect to Vss?

2.If i did as above, what are consequences?

3.Does it effect RESET function of controller?

[mƎALLEm]

Hello,

Why do you need to connect VDDA and VREF+ to VSS and not to VDD?

[Deviprasad Bokkisam]

We want miniature(small size) design for our project. If we connect VDDA and VREF+ to VDD, we need passive components inductor and capacitor which takes some space in PCB. We taught that, if we connect VDDA and VREF+ to Vss we can eliminate passive components so that PCB will be miniaturized. Off course we don't need ADC and DAC for our project. Please update your comments for my queries.

[Tesla DeLorean]

Noise into the ADC/DAC shouldn't be an issue in this context. The VCO, PLL and POR do need power. The other bulk and decoupling for the primary supply should suffice if placed tightly.

Still need bulk capacitance at VCAP pins.

Would suggest doing a design review with local FAE prior to sign off.

 

 

[RomainR.]

Hello @Deviprasad Bokkisam 

1) Connect VDDA, VREF+, VSSA to VSS?
No, even if you do not use the analog domain, you must connect these power supplies VDDA/VSSA and VREF+/VREF- as explained in the AN5419 in Table 2 and figure 3.

2) What are consequences?
STM32H3 will not work.

3) Does it affect RESET function
And not only that, it affects all power integrity of the device.

Best regards,
romain

[Deviprasad Bokkisam]

Thank you for reply.

In AN5419 in table2 given as, VDDA voltage range 0 to 3.6V and commented as "DAC, ADC, OPAMP, COMP, VREFBUF are not used. " ,So from this comment it may be possible to connect VDDA, VREF+ and VSSA to VSS(ground).Please confirm.

[Tesla DeLorean]

The part would be unusable, debug tool would not connect, firmware can't be written or run.

Ability to rework the BGA and PCB being low I'd expect you'd need to scrap and redo.