PIC12F635ESLASHST datasheet(64/196 Pages) MICROCHIP

64 / 196 page

PIC12F635/PIC16F636/639

DS41232B-page 62

Preliminary

7.1

Comparator Operation

A single comparator is shown in Figure 7-1 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 7-1 represent

the uncertainty due to input offsets and response time.

The polarity of the comparator output can be inverted

by setting the CxINV bits (CMCON0<5:4>). Clearing

CxINV results in a non-inverted output. A complete

table showing the output state versus input conditions

and the polarity bit is shown in Table 7-1.

TABLE 7-1:

OUTPUT STATE VS. INPUT

CONDITIONS

FIGURE 7-1:

SINGLE COMPARATOR

7.2

Analog Input Connection

Considerations

A simplified circuit for an analog input is shown in

Figure 7-2. 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 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 7-2:

ANALOG INPUT MODEL

Note:

To use CIN+ and CIN- pins as analog

inputs, the appropriate bits must be

programmed

the

CMCON0

(19h)

Input Conditions

CINV

CxOUT

VIN- > VIN+

VIN- < VIN+

VIN- > VIN+

VIN- < VIN+

Note 1: When reading the Port register, all pins

configured as analog inputs will read as a

‘0’. Pins configured as digital inputs will

convert as analog inputs according to the

input specification.

2: Analog levels on any pin defined as a

digital input may cause the input buffer to

consume more current than is specified.

–

VIN+

VIN-

Output

VIN–

VIN+

Output

VIN+

VIN-

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

Rs < 10 k

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