Datasheet

Electrical characteristics STM32F405xx, STM32F407xx
120/167 Doc ID 022152 Rev 2
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 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 currents.
Any positive injection current within the limits specified for I
INJ(PIN)
and ΣI
INJ(PIN)
in
Section 5.3.16 does not affect the ADC accuracy.
Table 66. ADC accuracy at f
ADC
= 30 MHz
(1)
1. Better performance could be achieved in restricted V
DD
, frequency and temperature ranges.
Symbol Parameter Test conditions Typ Max
(2)
2. Based on characterization, not tested in production.
Unit
ET Total unadjusted error
f
PCLK2
= 60 MHz,
f
ADC
= 30 MHz, R
AIN
< 10 kΩ,
V
DDA
= 1.8
(3)
to 3.6 V
3. If an inverted reset signal is applied to PDR_ON, this value can be lowered to 1.7 V when the device
operates in a reduced temperature range (0 to 70 °C).
±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
–=