STM32F407VGT6 - ADC pins unused ?(VREF+,VREF-,VDDA,VSSA)

[testid360]

Posted on April 03, 2014 at 17:45

Hello everyone, i am trying to design a board around STM32F407VGT6 and i want to use minimum components. i will not use the ADC for any purpose , is it possible to leave the pins related to it (VREF+,VREF-,VDDA,VSSA) unconnected ?

#stm32-stm32f4-adc-vref+ #stm32-vref+-analog

[Tesla DeLorean]

Posted on April 03, 2014 at 18:15

Connecting pins to a supply does not constitute a ''component'', or any significant burden on a PCB design.

You need to connect the VSSA/VDDA supplies, as these also control the power-on-reset circuitry.

[jpeacock2399]

Posted on April 04, 2014 at 15:45

The VDDA and VSSA are used by the PLL so you have to connect them.  Without VREF pins there's no ADC, and no way to use the internal voltage reference (a great tool for monitoring the logic supply voltage) or CPU temperature sensor.  This is not the place to save components, connect all the analog pins.

  Jack Peacock

[testid360]

Posted on April 06, 2014 at 15:19

Thanks Clive1 and Jack , i made the mistake of associating Analog pins to only the ADC .

I'll Connect them appropriately in my circuit.Special Thanks to Clive1 for replying within half an hour. That is just amazing .

[HermannKleier]

Posted on April 22, 2014 at 12:32

I was developing for the STM32F0xxx when I tripped over the same question. There the documentation (AN4080, section 1.1 Power supply schemes) is quite explicit. It says:

The

VDDA

voltage level must always be greater than or equal to the VDD voltage level and must be provided first. The documentation of the STM32L053x6 (DM00105960, section 6.3.1 General operating conditions) is quite clear too:It is recommended to power VDD and VDDA from the same source. A maximum difference of 300 mV between VDD and VDDA can be tolerated during power-up and normal operation. Because the internal RC oscillator is required when booting, the reference manual of the STM32L0 family (RM0367, section 6.1 Power supplies) says that an STM32L0xx cannot boot without VDDA:VDDA is the external analog power supply for ADC, DAC, reset blocks, RC oscillators and PLL. Alas, I could not find such clear statements in the documentation of the STM32F4 family.

[Tesla DeLorean]

Posted on April 22, 2014 at 16:13

Alas, I could not find such clear statements in the documentation of the STM32F4 family.

But there is a big diagram that clearly indicates the RC/PLL are in the analogue power domain, and prose that describes the Power-On-Reset association to VDDA, so it's not a particularly huge leap to assume the part won't actually start absent an analogue supply. The change in the F0 documentation no doubt in response to dealing with people who failed to glean the salient details from reference and data manuals. Connecting NRST to the supply will also induce failure.