S6J311E Datasheet, PDF (103/116 Pages) Cypress Semiconductor – 32-Bit Traveo™ Family S6J3110 Series Microcontroller Datasheet

S6J311E, S6J311D, S6J311C, S6J311B
10.11.2 Notes on Using A/D Converter
About the Output Impedance of an External Circuit for Analog Input
When the external impedance is too high, the analog voltage sampling time may become insufficient. In this case, we recommend
attaching a capacitor (about 0.1 µF) to an analog input pin.
Analog input circuit model
Source
Rext
Cext
Analog input
Rint
Cint
Comparator
Rint
Cint
Rext
Cext
: Analog input impedance
3.9 kiloohms (max) (4.5 V≤AVcc≤5.25 V)
: Capacitance of MCU input pin
11.0pF (max) (4.5 V≤AVcc≤5.25 V)
: External driving impedance
: Capacitance of PCB at A/D converter input
The following approximation formula for the replacement model above can be used:
sampling time (minimum) = 9 x ( (Rin + Rext ) x Cin + Rext x Cext )
Note: Listed values must be considered as reference values.
Document Number: 002-05681 Rev.*A
Page 103 of 116