S42 Hardware User Guide
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Page 41 of 62
5.4.5
Analog ADC Input AIN
When the ADC is not sampling the AIN input pin has very high impedance and can be
regarded as open circuit.
Table 14 shows the internal impedance for AIN during
sampling for different prescaler settings.
This impedance has to be taken into account when using additional external voltage dividers.
Prescaler
Impedance R
AIN
Unit
min.
typ.
Max.
1 / 1
120
130
140
k
Ω
2 / 3
180
195
210
k
Ω
1 / 3
365
390
415
k
Ω
Table 14: Input Impedance for AIN
Maximum allowed input voltage at AIN:
(Both of the following rules have to be fulfilled)
•
The ADC may not be exposed to voltages >2,4V after the AIN prescaler
and
•
The AIN pin must not be exposed to voltages >VDD + 0,3V