Datasheet

PIC18F66K80 FAMILY
DS39977F-page 376  2010-2012 Microchip Technology Inc.
24.2 Comparator Operation
A single comparator is shown in Figure 24-2, along with
the relationship between the analog input levels and
the digital output. When the analog input at V
IN+ is less
than the analog input, V
IN-, the output of the compara-
tor is a digital low level. When the analog input at V
IN+
is greater than the analog input, V
IN-, the output of the
comparator is a digital high level. The shaded areas of
the output of the comparator in Figure 24-2 represent
the uncertainty due to input offsets and response time.
FIGURE 24-2: SINGLE COMPARATOR
24.3 Comparator Response Time
Response time is the minimum time, after selecting a
new reference voltage or input source, before the com-
parator output has a valid level. The response time of
the comparator differs from the settling time of the volt-
age reference. Therefore, both of these times must be
considered when determining the total response to a
comparator input change. Otherwise, the maximum
delay of the comparators should be used (see
Section 31.0 “Electrical Characteristics”).
24.4 Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 24-3. Since the analog pins are connected to a
digital output, they have reverse biased 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 condition may
occur.
A maximum source impedance of 10 k
 is
recommended for the analog sources. Any external
component connected to an analog input pin, such as
a capacitor or a Zener diode, should have very little
leakage current.
FIGURE 24-3: COMPARATOR ANALOG INPUT MODEL
Output
V
IN-
V
IN+
–
+
VIN+
V
IN-
Output
VA
R
S
AIN
CPIN
5 pF
V
DD
VT = 0.6V
V
T = 0.6V
R
IC
ILEAKAGE
±100 nA
V
SS
Legend: CPIN = Input Capacitance
V
T = Threshold Voltage
I
LEAKAGE = Leakage Current at the pin due to various junctions
R
IC = Interconnect Resistance
R
S = Source Impedance
VA = Analog Voltage
Comparator
Input
<10 k