AN2834 datasheet(21/45 Pages) STMICROELECTRONICS

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AN2834

How to get the best ADC accuracy

because the series resistance of the wire is very low. At high frequencies, however, the

impedance is high.

STM32x side

In most STM32x microcontrollers the VDD and VSS pins are placed close to each other. So

are the VREF+ and VSSA pins. A capacitor can therefore be connected very close to the

microcontroller with very short leads. For multiple VDD and VSS pins, use separate

decoupling capacitors.

The VDDA pin must be connected to two external decoupling capacitors (10 nF Ceramic +

1 µF Tantalum or Ceramic). See Figure 20 and Figure 21 for decoupling examples.

For STM32x devices delivered in 100/144-pin packages, it is possible to improve the

accuracy on low-voltage inputs by connecting a separate external ADC reference voltage

input on VREF+ (refer to Section 3.2.5). The voltage on VREF+ may range from 2.4 V to

VDDA. If a separate, external reference voltage is applied on VREF+, two 10 nF and 1 µF

capacitors must be connected on this pin. In all cases, VREF+ must be kept between 2.4 V

and VDDA.

Figure 20. Power supply and reference decoupling for 100- and 144-pin packages

Figure 21. Power supply decoupling for 36-, 48- and 64-pin packages

1 μF // 10 nF

VDDA

VREF+

VREF–

VSSA

VREF+ not connected to VDDA

VREF+ connected to VDDA

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1 μF // 10 nF

VDDA

VSSA

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AN2834 Datasheet(PDF) 21 Page - STMicroelectronics