Datasheet

PIC16F631/677/685/687/689/690
DS41262E-page 100 © 2008 Microchip Technology Inc.
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 con-
nection with a digital input, they have reverse biased
ESD protection diodes to V
DD and VSS. The analog
input, therefore, must be between V
SS 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 8-6: ANALOG INPUT MODEL
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.
VA
Rs < 10K
C
PIN
5 pF
VDD
VT ≈ 0.6V
V
T ≈ 0.6V
RIC
ILEAKAGE
(1)
Vss
AIN
Legend: CPIN = Input Capacitance
I
LEAKAGE = Leakage Current at the pin due to various junctions
R
IC = Interconnect Resistance
R
S = Source Impedance
V
A = Analog Voltage
V
T = Threshold Voltage
To Comparator
Note 1: See Section 17.0 “Electrical Specifications”