STM CircleOS forum / Separate VDD and VDDA supply, with different voltage

Jay2 · 2008-09-24 19:38:17

Hi all!

I'm develloping a board with 2.0V at VDD of the STM32. I would, however, like to use the onboard ADCs. To do so, it is clearly specified that I need a VDD of at least 2.4V.

Can I supply the STM32 VDD with 2.0V and the VDDA with 3.3V and have working ADCs?

Thanks,
-Jay2

ZHA · 2008-10-29 16:07:17

From the STM32 datasheet:

Power supply schemes
● VDD = 2.0 to 3.6 V: external power supply for I/Os and the internal regulator.
Provided externally through VDD pins.
● VSSA, VDDA = 2.0 to 3.6 V: external analog power supplies for ADC, Reset blocks, RCs
and PLL (minimum voltage to be applied to VDDA is 2.4 V when the ADC is used). VDDA and VSSA must be connected to VDD and VSS, respectively.

Jay2 · 2008-10-29 16:39:36

This does not answer directly, let me rephrase my question:
Can I have two different supplies where VDDA is greater thant VDD? One at 2.0V for VDD and one at 2.5V for VDDA?

If VDD must be connected to VDDA, then no separate supplies can coexist. If they can be separate, is it correct to feed them different voltage? To wich extend?

Thanks,
Jay2

ZHA · 2008-10-30 08:53:37

no You can not because the VDDA and VSSA must be connected to VDD and VSS, respectively.
But to improve conversion accuracy, the ADC has an independent power supply which can be separately filtered and shielded from noise on the PCB.
For more details refer to STM32 Reference manual sections" Power Supplies" and "ADC functional description" table 41

# 1 2008-09-24 19:38:17 Separate VDD and VDDA supply, with different voltage

Separate VDD and VDDA supply, with different voltage

# 2 2008-10-29 16:07:17 Separate VDD and VDDA supply, with different voltage

Re: Separate VDD and VDDA supply, with different voltage

# 3 2008-10-29 16:39:36 Separate VDD and VDDA supply, with different voltage

Re: Separate VDD and VDDA supply, with different voltage

# 4 2008-10-30 08:53:37 Separate VDD and VDDA supply, with different voltage

Re: Separate VDD and VDDA supply, with different voltage

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