STM32F051K6 datasheet(78/104 Pages) STMICROELECTRONICS

78 / 104 page

STM32F051x

Electrical characteristics

Doc ID 022265 Rev 3

79/105

Figure 22.

ADC accuracy characteristics

Figure 23.

Typical connection diagram using the ADC

Refer to Table 54 for the values of RAIN, RADC and CADC.

Cparasitic represents the capacitance of the PCB (dependent on soldering and PCB layout quality) plus the

pad capacitance (roughly 7 pF). A high Cparasitic value will downgrade conversion accuracy. To remedy

this, fADC should be reduced.

General PCB design guidelines

Power supply decoupling should be performed as shown in Figure 10. The 10 nF capacitor

should be ceramic (good quality) and it should be placed as close as possible to the chip.

ADC Accuracy vs. Negative Injection Current: Injecting negative current on any of the standard (non-

robust) analog input pins should be avoided as this significantly reduces the accuracy of the conversion

being performed on another analog input. It is recommended to add a Schottky diode (pin to ground) to

standard analog pins which may potentially inject negative current.

Any positive injection current within the limits specified for IINJ(PIN) and ΣIINJ(PIN) in Section 6.3.13 does not

affect the ADC accuracy.

Better performance may be achieved in restricted VDDA, frequency and temperature ranges.

Data based on characterization results, not tested in production.

1LSBIDEAL

(1) Example of an actual transfer curve

(2) The ideal transfer curve

(3) End point correlation line

ET=Total Unadjusted Error: maximum deviation

between the actual and the ideal transfer curves.

EO=Offset Error: deviation between the first actual

transition and the first ideal one.

EG=Gain Error: deviation between the last ideal

transition and the last actual one.

ED=Differential Linearity Error: maximum deviation

between actual steps and the ideal one.

EL=Integral Linearity Error: maximum deviation

between any actual transition and the end point

correlation line.

4095

4094

4093

4093 4094 4095 4096

(1)

(2)

(3)

VDDA

VSSA

1LSBIDEAL

VDDA

AINx

IL±1 μA

0.6 V

RAIN(1)

Cparasitic

VAIN

0.6 V

RADC(1)

12-bit

converter

CADC(1)

Sample and hold ADC

converter

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