VDDA/VSSA connection to VDD/VSS

[Pavel Krupets]

RM0038 Reference manual

STM32L100xx, STM32L151xx, STM32L152xx and STM32L162xx advanced ARM®-based 32-bit MCUs

Figure 8. Power supply overview

(LQFTP100)

has the following note:

1. VDDA and VSSA must be connected to VDD and VSS, respectively.

If I am using separate supply for VDDA should I still connect them?

Table 58. ADC pins

has the following:

2.4 V ≤ VDDA ≤ VDD (3.6 V) for full speed

It means VDDA can be less than VDD.

Manual is a bit confusing. Please help! Which one is a correct statement:

1. VDDA doesn't need to be connected to VDD and can be different from it
2. VDDA must be connected to VDD

[Pavel Krupets]

No problem! thanks for the help! I couldn't find anything about tying VDDA and VDD in STM32L4 data sheet. Though it has fewer ADCs.

Might need to reduce ADC speed so I can use VREF+ = 2.5V and VDDA = 3.3V.

Still don't understand why do we need VDDA pin if it is going to be tied to VDD. Oh well.

[jose luu]

VDDA could be derived using a low noise LDO from VDD