PIC16F636-I Datasheet, PDF (75/234 Pages) Microchip Technology – 8/14-Pin, Flash-Based 8-Bit CMOS Microcontrollers with nanoWatt Technology

PIC12F635/PIC16F636/639
7.2 Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 7-5. Since the analog input pins share their con-
nection 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 kΩ 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 7-5:
ANALOG INPUT MODEL
VDD
Rs < 10K
VT ≈ 0.6V
AIN
VA
CPIN
5 pF
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
±500 nA
To Comparator
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
© 2007 Microchip Technology Inc.
DS41232D-page 73