Datasheet

DocID022152 Rev 8 135/202
STM32F405xx, STM32F407xx Electrical characteristics
Equation 1: R
AIN
max formula
The formula above (Equation 1) is used to determine the maximum external impedance
allowed for an error below 1/4 of LSB. N = 12 (from 12-bit resolution) and k is the number of
sampling periods defined in the ADC_SMPR1 register.
a
Note: ADC accuracy vs. negative injection current: injecting a negative current on any 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 analog pins which may potentially inject negative currents.
Any positive injection current within the limits specified for I
INJ(PIN)
and SI
INJ(PIN)
in
Section 5.3.16 does not affect the ADC accuracy.
Table 68. ADC accuracy at f
ADC
= 30 MHz
Symbol Parameter Test conditions Typ Max
(1)
1. Guaranteed by characterization.
Unit
ET Total unadjusted error
f
PCLK2
= 60 MHz,
f
ADC
= 30 MHz, R
AIN
< 10 kΩ,
V
DDA
= 1.8
(2)
to 3.6 V
2. V
DD
/V
DDA
minimum value of 1.7 V is obtained when the device operates in reduced temperature range,
and with the use of an external power supply supervisor (refer to Section : Internal reset OFF).
±2 ±5
LSB
EO Offset error ±1.5 ±2.5
EG Gain error ±1.5 ±3
ED Differential linearity error ±1 ±2
EL Integral linearity error ±1.5 ±3
R
AIN
k0.5–()
f
ADC
C
ADC
2
N 2+
()ln××
---------------------------------------------------------------- R
ADC
–=