Microchip Technology MCU PIC PIC18F87K22-I/PTRSL TQFP-80 MCP PIC18F87K22-I/PTRSL Data Sheet
Product codes
PIC18F87K22-I/PTRSL
PIC18F87K22 FAMILY
DS39960D-page 370
2009-2011 Microchip Technology Inc.
24.2
Comparator Operation
A single comparator is shown in
, along with
the relationship between the analog input levels and
the digital output. When the analog input at V
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
the output of the comparator, in
, 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
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
24.4
Analog Input Connection
Considerations
Considerations
A simplified circuit for an analog input is shown in
. Since the analog pins are connected to a
digital output, they have reverse biased diodes to V
DD
and V
SS
. The analog input, therefore, must be between
V
SS
and V
DD
. 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
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.
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
+
–
+
V
IN
+
V
IN
-
Output
VA
R
S
A
IN
C
PIN
5 pF
V
DD
V
T
= 0.6V
V
T
= 0.6V
R
IC
I
LEAKAGE
±100 nA
V
SS
Legend:
C
PIN
= 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
Input
<10k