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Yusuf
Yusuf
Associate II
June 11, 2024
Question

Choosing ADC Reference Voltage

Hello,

 

My problem is that I have a custom STM32WB55RG board and I want to use ADC reference voltage as 1V or as close as possible to 1 V. My questions are:

1- In datasheet, it states that "If VDDA> 2V, it should be 2<Vref<VDDA and if VDDA<2V, Vref should be equal to VDDA". If I decrease VDDA to 1.7 which is around its minimum,1.62V, could there be a problem with other peripherals etc?

2- Not in STM32WB55 Datasheet but in other datasheets such as  "STM32F103x8 Datasheet Table 9", it states that VDD-VDDA should be maximum 300 mV". Is it valid for STM32WB55RG too? And if it is, could there be problem if I decrease VDD to around 1.8V?

3- Would using an external ADC with SPI protocol be a feasible solution?

 

I use SPI1,SPI2,ADC1,RTC,USB,I2C1,TIM16 and RF peripherals in my software and there is a RGB LED in the board.

 

Sincerely,

Yusuf.

This topic has been closed for replies.

5 replies

AScha.3
AScha.3
Super User
June 11, 2024

Hi,

>I want to use ADC reference voltage as 1V

Why you want this ? for what its needed?

+

1+2 ->

AScha3_0-1718099300937.png

So if you want USB working, you need 3.0V minimum supply (VDD, VDDA, VUSB...all.)

AScha3_1-1718099563760.png

 

and you could use Vref from external source as low as 2,0V . Thats it.

If you just want an 0..1V input range with best resolution, set VDD...VRef to 3.0V

and use an opamp (gain =3) to get , what you want.

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Yusuf
YusufAuthor
Associate II
June 14, 2024

Hello,

 

Thank you for your reply. Regarding noise and are problems, I don't want to use an pre-amplifier. My question is that I assume I can use VREFBUF in normal mode to get 2.048 V reference voltage internally or (VDDA-150 mV) if I use VREF in degraded mode. Is it feasible to use that by decreasing VDDA to 1.7 V?

 

Sincerely,

Yusuf.

AScha.3
AScha.3
Super User
June 14, 2024

No.

2,4V minimum, if using vrefbuf. (btw how should it do 2.x V ref, if supply is lower than that ? magic ? )

AScha3_0-1718376551050.png

 

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