Datasheet

R
AIN
T
S
f
ADC
C
ADC
2
N2+
()ln××
--------------------------------------------------------------- - R
ADC
–<
Electrical characteristics STM32L431xx
134/200 DocID028800 Rev 1
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).
Table 65. Maximum ADC RAIN
(1)(2)
Resolution
Sampling cycle
@80 MHz
Sampling time [ns]
@80 MHz
RAIN max (Ω)
Fast channels
(3)
Slow channels
(4)
12 bits
2.5 31.25 100 N/A
6.5 81.25 330 100
12.5 156.25 680 470
24.5 306.25 1500 1200
47.5 593.75 2200 1800
92.5 1156.25 4700 3900
247.5 3093.75 12000 10000
640.5 8006.75 39000 33000
10 bits
2.5 31.25 120 N/A
6.5 81.25 390 180
12.5 156.25 820 560
24.5 306.25 1500 1200
47.5 593.75 2200 1800
92.5 1156.25 5600 4700
247.5 3093.75 12000 10000
640.5 8006.75 47000 39000
8 bits
2.5 31.25 180 N/A
6.5 81.25 470 270
12.5 156.25 1000 680
24.5 306.25 1800 1500
47.5 593.75 2700 2200
92.5 1156.25 6800 5600
247.5 3093.75 15000 12000
640.5 8006.75 50000 50000
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