Electrical characteristics
Equation 1: R
AIN
max formula:
T
S
R
AIN
<
--------------------------------------------------------------- –
R
ADC
-
N+2
f
ADC
×
C
ADC
×
ln
(
2
)
STM32F103xC, STM32F103xD, STM32F103xE
The formula above (Equation
1)
is used to determine the maximum external impedance allowed for an
error below 1/4 of LSB. Here N = 12 (from 12-bit resolution).
Table 58.
R
AIN
max for f
ADC
= 14 MHz
(1)
T
s
(cycles)
t
S
(µs)
0.11
0.54
0.96
2.04
2.96
3.96
5.11
17.1
1.2
10
19
41
60
80
104
350
R
AIN
max (kΩ)
1.5
7.5
13.5
28.5
41.5
55.5
71.5
239.5
1. Data guaranteed by design, not tested in production.
Table 59.
Symbol
ET
EO
EG
ED
EL
ADC accuracy - limited test conditions
(1)
Parameter
Total unadjusted error
(3)
Offset error
Gain error
Differential linearity error
Integral linearity error
Test conditions
f
PCLK2
= 56 MHz,
,
f
ADC
= 14 MHz, R
AIN
< 10 kΩ
V
DDA
= 3 V to 3.6 V
T
A
= 25 °C
Measurements made after
ADC calibration
V
REF+
= V
DDA
Typ
±1.3
±1
±0.5
±0.7
±0.8
Max
(2)
±2
±1.5
±1.5
±1
±1.5
LSB
Unit
1. ADC DC accuracy values are measured after internal calibration.
2. Data based on characterization, not tested in production.
3. 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 I
INJ(PIN)
and
ΣI
INJ(PIN)
in
does not
affect the ADC accuracy.
100/118
STMICROELECTRONICS [ STMICROELECTRONICS ]
