PIC18F87J11_12 Datasheet, PDF (322/466 Pages) Microchip Technology – 64/80-Pin, High-Performance, 1-Mbit Flash Microcontrollers

PIC18F87J11 FAMILY
23.2 Comparator Operation
A single comparator is shown in Figure 23-2, along with
the relationship between the analog input levels and
the digital output. When the analog input at VIN+ is less
than the analog input VIN-, the output of the comparator
is a digital low level. When the analog input at VIN+ is
greater than the analog input VIN-, the output of the
comparator is a digital high level. The shaded areas of
the output of the comparator in Figure 23-2 represent
the uncertainty due to input offsets and response time.
FIGURE 23-2:
SINGLE COMPARATOR
VIN+
+
VIN-
–
Output
VIN-
VIN+
Output
23.3 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 28.0 “Electrical Characteristics”).
23.4 Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 23-3. Since the analog pins are connected to a
digital output, they have reverse biased 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 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 23-3:
COMPARATOR ANALOG INPUT MODEL
VDD
RS < 10k
VT = 0.6V
RIC
AIN
VA
CPIN
5 pF
VT = 0.6V
ILEAKAGE
±500 nA
Comparator
Input
VSS
Legend:
CPIN
=
VT
=
ILEAKAGE =
RIC
=
RS
=
VA
=
Input Capacitance
Threshold Voltage
Leakage Current at the pin due to various junctions
Interconnect Resistance
Source Impedance
Analog Voltage
DS39778E-page 322
 2007-2012 Microchip Technology Inc.