PIC18F2331 Datasheet, PDF (256/396 Pages) Microchip Technology – 28/40/44-Pin Enhanced Flash Microcontrollers with nanoWatt Technology, High Performance PWM and A/D

PIC18F2331/2431/4331/4431
EXAMPLE 20-1: CALCULATING THE MINIMUM REQUIRED ACQUISITION TIME
TACQ
=
TAMP + TC + TCOFF
TAMP
=
negligible
TCOFF =
(Temp – 25°C)(0.005 µs/°C)
(50°C – 25°C)(0.005 µs/°C) = .13 µs
Temperature coefficient is only required for temperatures > 25°C. Below 25°C, TCOFF = 0 µs.
TC
–
-(CHOLD) (RIC + RSS + RS) ln(1/2047) µs
-(9 pF) (1 kΩ + 6 kΩ + 100 Ω) ln(0.0004883) µs = .49 µs + .13 µs = .62 µs
TACQ
=
0 + .62 µs + .13 µs = .75 µs
Note: If the converter module has been in Sleep mode, TAMP is 2.0 µs from the time the part exits Sleep mode.
FIGURE 20-2:
ANALOG INPUT MODEL
VDD
Rs ^ANx
VT = 0.6V
RIC ≤ 1k
Sampling
Switch
SS _RSS
VAIN
CPIN
5 pF
VT = 0.6V
I leakage
± 500 nA
CHOLD = 9 pF
VSS
Legend: CPIN
= input capacitance
VT
= threshold voltage
I LEAKAGE = leakage current at the pin due to
various junctions
RIC
= interconnect resistance
SS
= sampling switch
CHOLD = sample/hold capacitance (from DAC)
RSS
= sampling switch resistance
6V
5V
VDD 4V
3V
2V
5 6 7 8 9 10 11
Sampling Switch (kΩ)
Note: For VDD < 2.7V and temperatures below 0ºC, VAIN should be restricted to range: VAIN < VDD/2.
DS39616B-page 254
Preliminary
 2003 Microchip Technology Inc.