ST STM32 Application Note

How to get the best ADC accuracy AN2834
46/49 DocID15067 Rev 3
Figure 38. Parasitic capacitances of sampling switch
This charging and discharging currents (PMOS and NMOS asymmetric capacitances) can
cause charge transfer to sampling capacitor C
sh
.
Internal charging of sampling capacitor
It is possible that after the conversion process (successive approximation process in SAR
type of ADC) the sample and hold capacitor C
sh
is charged to some voltage. The reason
can be:
• some leakage current to C
sh
(parasitic current inside ADC structure, see Figure 39)
• residual charge transfer from the switches when ADC structure is switched back to
default state before next conversion
• other reasons (related to internal ADC parasitic structures)
Figure 39. Parasitic current example inside ADC structure
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ST STM32 Specifications

General

Series	STM32
Category	Microcontrollers
Core	ARM Cortex-M0, Cortex-M0+, Cortex-M3, Cortex-M4, Cortex-M7, Cortex-M33
Clock Speed	Up to 480 MHz
GPIO Pins	Up to 144
Communication Interfaces	I2C, SPI, USART, USB, CAN, Ethernet
Package Types	LQFP, BGA, WLCSP
ADC Resolution	12-bit, 16-bit (varies by series)
DAC Resolution	12-bit (varies by series)
Operating Temperature	-40°C to +85°C or +105°C