PIC18F2331_07 Datasheet, PDF (258/400 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 + 100Ω) ln(0.0004883) μs = .49 μs
TACQ = 0 + .49 μs + .13 μs = .62 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
ILEAKAGE
±500 nA
CHOLD = 9 pF
VSS
Legend:
CPIN
= Input Capacitance
VT
= Threshold Voltage
ILEAKAGE = 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 0°C, VAIN should be restricted to range: VAIN < VDD/2.
DS39616C-page 256
Preliminary
© 2007 Microchip Technology Inc.