AN2834 datasheet(18/45 Pages) STMICROELECTRONICS

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ADC errors

AN2834

18/45

DocID15067 Rev 2

2.2.8

Injection current effect

A negative injection current on any analog pin (or a closely positioned digital input pin) may

introduce leakage current into the ADC input. The worst case is the adjacent analog

channel. A negative injection current is introduced when VAIN < VSS, causing current to flow

out from the I/O pin. This is illustrated in Figure 17.

Figure 17. Effect of injection current

2.2.9

Temperature influence

The temperature has a major influence on ADC accuracy. Mainly it leads to two major

errors: offset error drift and gain error drift. Those errors can be compensated in the

microcontroller firmware (refer to Section 3.2.8 for the temperature-compensation methods).

2.2.10

I/O pin crosstalk

Switching the I/Os may induce some noise in the analog input of the ADC due to capacitive

coupling between I/Os. Crosstalk may be introduced by PCB tracks that run close to each

other or that cross each other.

Internally switching digital signals and I/Os introduces high-frequency noise. Switching high-

sink I/Os may induce some voltage dips in the power supply caused by current surges. A

digital track that crosses an analog input track on the PCB may affect the analog signal (see

Figure 18).

Figure 18. Crosstalk between I/O pins

Case 1: Digital and analog signal tracks that pass close to each other.

Case 2: Digital and analog signal tracks that cross each other on a different PCB side.

STM32

Injection

current

leakage

current

AIN0

VAIN0

RAIN0

AIN1

VAIN < VSS

VSSA

ai15484

Analog

Digital

I/O

Case 1

Case 2

Analog

Digital

I/O

STM32

ai15485

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