Datasheet

R
AIN
T
S
f
ADC
C
ADC
2
N2+
()ln××
-------------------------------------------------------------- R
ADC
–<
DocID027114 Rev 2 69/88
STM32F070xB STM32F070x6 Electrical characteristics
75
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. Here N = 12 (from 12-bit resolution).
t
STAB
(2)
Power-up time 0 0 1 μs
t
CONV
(2)
Total conversion time
(including sampling time)
f
ADC
= 14 MHz 1 - 18 μs
14 to 252 (t
S
for sampling +12.5 for
successive approximation)
1/f
ADC
1. During conversion of the sampled value (12.5 x ADC clock period), an additional consumption of 100 μA on I
DDA
and 60 μA
on I
DD
should be taken into account.
2. Guaranteed by design, not tested in production.
Table 50. ADC characteristics (continued)
Symbol Parameter Conditions Min Typ Max Unit
Table 51. R
AIN
max for f
ADC
= 14 MHz
T
s
(cycles) t
S
(μs) R
AIN
max (kΩ)
(1)
1.5 0.11 0.4
7.5 0.54 5.9
13.5 0.96 11.4
28.5 2.04 25.2
41.5 2.96 37.2
55.5 3.96 50
71.5 5.11 NA
239.5 17.1 NA
1. Guaranteed by design, not tested in production.
Table 52. ADC accuracy
(1)(2)(3)
Symbol Parameter Test conditions Typ Max
(4)
Unit
ET Total unadjusted error
f
PCLK
= 48 MHz,
f
ADC
= 14 MHz, R
AIN
< 10 kΩ
V
DDA
= 2.7 V to 3.6 V
T
A
= −40 to 85 °C
±3.3 ±4
LSB
EO Offset error ±1.9 ±2.8
EG Gain error ±2.8 ±3
ED Differential linearity error ±0.7 ±1.3
EL Integral linearity error ±1.2 ±1.7
1. ADC DC accuracy values are measured after internal calibration.
2. 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 Section 6.3.14 does not affect the ADC
accuracy.
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