PIC16F882_12 Datasheet, PDF (95/338 Pages) Microchip Technology – 28/40/44-Pin Flash-Based, 8-Bit CMOS Microcontrollers

PIC16F882/883/884/886/887
8.7 Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 8-6. Since the analog input pins share their
connection with a digital input, they have reverse
biased ESD protection diodes to VDD and VSS. The
analog input, therefore, must be between VSS and VDD.
If the input voltage deviates from this range by more
than 0.6V in either direction, one of the diodes is
forward biased and a latch-up may occur.
A maximum source impedance of 10 k is recommended
for the analog sources. Also, any external component
connected to an analog input pin, such as a capacitor or
a Zener diode, should have very little leakage current to
minimize inaccuracies introduced.
FIGURE 8-6:
ANALOG INPUT MODEL
VDD
Rs < 10K
VA
AIN
CPIN
5 pF
VT  0.6V
VT  0.6V
Note 1: When reading a PORT register, all pins
configured as analog inputs will read as a
‘0’. Pins configured as digital inputs will
convert as an analog input, according to
the input specification.
2: Analog levels on any pin defined as a
digital input, may cause the input buffer to
consume more current than is specified.
RIC
ILEAKAGE⁽¹⁾
±500 nA
To ADC Input
Vss
Legend:
CPIN = Input Capacitance
ILEAKAGE = Leakage Current at the pin due to various junctions
RIC
= Interconnect Resistance
RS
= Source Impedance
VA
= Analog Voltage
VT
= Threshold Voltage
Note 1: See Section 17.0 “Electrical Specifications”.
 2006-2012 Microchip Technology Inc.
DS41291G-page 95