How was the recommended value of driving impedance to analog input in the hardware manual or data sheet calculated?
• Answer :When a 15.5 kΩ external circuit exists at the A/D port (3.2 kΩ, 30 pF: Internal circuit constant) • t = CR = (3.2 kΩ + 15.5 kΩ) x 30 pF = 561ns The time constant is a time at 63.2% charging voltage, so the time that is 8 to 10 times the charging time is actually required.561ns x 8 ≈ 4 us → Actual charging timeIn microcomputer sampling time setting, the fastest 4 us sampling time (64 cycles: at 16 MHz) can be satisfied.
