Datasheet

 2003-2013 Microchip Technology Inc. DS39609C-page 227
PIC18F6520/8520/6620/8620/6720/8720
20.7 Comparator Operation
During Sleep
When a comparator is active and the device is placed
in Sleep mode, the comparator remains active and the
interrupt is functional, if enabled. This interrupt will
wake-up the device from Sleep mode, when enabled.
While the comparator is powered up, higher Sleep
currents than shown in the power-down current
specification will occur. Each operational comparator
will consume additional current, as shown in the com-
parator specifications. To minimize power consumption
while in Sleep mode, turn off the comparators
(CM<2:0> = 111) before entering Sleep. If the device
wakes up from Sleep, the contents of the CMCON
register are not affected.
20.8 Effects of a Reset
A device Reset forces the CMCON register to its Reset
state, causing the comparator module to be in the Com-
parator Reset mode, CM<2:0> = 000. This ensures
that all potential inputs are analog inputs. Device cur-
rent is minimized when analog inputs are present at
Reset time. The comparators will be powered down
during the Reset interval.
20.9 Analog Input Connection
Considerations
A simplified circuit for an analog input is shown in
Figure 20-4. 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
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 20-4: COMPARATOR ANALOG INPUT MODEL
VA
RS < 10k
A
IN
CPIN
5 pF
VDD
VT = 0.6V
VT = 0.6V
RIC
ILEAKAGE
±500 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