
PIC16C717/770/771
DS41120B-page 114
2002 Microchip Technology Inc.
EXAMPLE 11-3:
CALCULATING THE
MINIMUM
REQUIRED SAMPLE TIME
FIGURE 11-5: ANALOG INPUT MODEL
TACQ =
Amplifier Settling Time
+ Holding Capacitor Charging Time
+Temperature offset
TACQ =5
s
+ TC
+ [(Temp - 25
°C)(0.05 s/°C)]
TC =
Holding Capacitor Charging Time
TC =(CHOLD) (RIC + RSS + RS) In (1/16384)
TC =
-25 pF (1 k
+10 k + 2.5 k) In (1/16384)
TC =
-25 pF (13.5 k
) In (1/16384)
TC =
-0.338 (-9.704)
s
TC =3.3
s
TACQ =5
s
+ 3.3
s
+ [(50
°C - 25°C)(0.05 s / °C)]
TACQ =
8.3
s + 1.25 s
TACQ =
9.55
s
The temperature coefficient is only required for
temperatures > 25
°C.
CPIN
VA
RS
Port Pin
5 pF
VDD
Vt = 0.6V
VT = 0.6V
ILEAKAGE
RIC ~ 1k
Sampling
Switch
SS
RSS
CHOLD = 25 pF
VSS
6V
Sampling Switch (RSS)
5V
4V
3V
2V
567 8 9 10 11
( k
)
VDD
± 100 nA
Legend CPIN
VT
ILEAKAGE
RIC
SS
CHOLD
= input capacitance
= threshold voltage
= leakage current at the pin due to
= interconnect resistance
= sampling switch
= sample/hold capacitance
various junctions
~