18F8680 datasheet(265/496 Pages) MICROCHIP

265 / 496 page

 2004 Microchip Technology Inc.

DS30491C-page 263

PIC18F6585/8585/6680/8680

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

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

Comparator

Reset

mode

(CM<2:0> = 000).

This

ensures that all potential inputs are analog inputs.

Device current 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

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

Ω 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

RS < 10k

AIN

CPIN

5 pF

VDD

VT = 0.6V

RIC

ILEAKAGE

±500 nA

VSS

Legend:CPIN

= Input Capacitance

= Threshold Voltage

ILEAKAGE = Leakage Current at the pin due to various junctions

RIC

= Interconnect Resistance

= Source Impedance

= Analog Voltage

Comparator

Input

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