PIC18F2331/2431/4331/4431
EXAMPLE 21-1:
CALCULATING THE MINIMUM REQUIRED ACQUISITION TIME
TACQ
TAMP
TCOFF
=
=
=
TAMP + TC + TCOFF
Negligible
(Temp – 25°C)(0.005 s/°C)
(50°C – 25°C)(0.005 s/°C) = .13 s
Temperature coefficient is only required for temperatures > 25°C. Below 25°C, TCOFF = 0 s.
TC
=
-(CHOLD) (RIC + RSS + RS) ln(1/2047) s
-(9 pF) (1 k + 6 k + 100) ln(0.0004883) s = .49 s
TACQ
=
0 + .49 s + .13 s = .62 s
Note: If the converter module has been in Sleep mode, TAMP is 2.0 s from the time the part exits Sleep mode.
FIGURE 21-2:
ANALOG INPUT MODEL
VDD
Sampling
Switch
VT = 0.6V
ANx
SS
RIC 1k
RSS
Rs
CPIN
VAIN
ILEAKAGE
±100 nA
CHOLD = 9 pF
VT = 0.6V
5 pF
VSS
Legend: CPIN
= Input Capacitance
= Threshold Voltage
6V
5V
VDD 4V
VT
ILEAKAGE = Leakage Current at the pin due to
various junctions
3V
RIC
= Interconnect Resistance
2V
SS
= Sampling Switch
CHOLD
RSS
= Sample/Hold Capacitance (from DAC)
= Sampling Switch Resistance
5
6
7
8 9 10 11
Sampling Switch (k)
Note:
For VDD < 2.7V and temperatures below 0°C, VAIN should be restricted to range: VAIN < VDD/2.
DS39616D-page 250
2010 Microchip Technology Inc.
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