PIC12F1822-ISLASHMF datasheet(164/398 Pages) MICROCHIP

164 / 398 page

PIC12F/LF1822/16F/LF1823

DS41413A-page 164

Preliminary

 2010 Microchip Technology Inc.

18.7

Comparator Negative Input

Selection

The CxNCH<1:0> bits of the CMxCON0 register direct

one of the analog pins to the comparator inverting

input.

18.8

Comparator Response Time

The comparator output is indeterminate for a period of

time after the change of an input source or the selection

of a new reference voltage. This period is referred to as

the response time. The response time of the comparator

differs from the settling time of the voltage reference.

Therefore, both of these times must be considered when

determining the total response time to a comparator

input change. See the Comparator and Voltage Refer-

ence Specifications in Section 29.0 “Electrical Specifi-

cations” for more details.

18.9

Interaction with ECCP Logic

The C1 and C2 comparators can be used as general

purpose comparators. Their outputs can be brought

out to the C1OUT and C2OUT pins. When the ECCP

Auto-Shutdown is active it can use one or both

comparators. If auto-restart is also enabled, the

comparators can be configured as a closed loop

analog feedback to the ECCP, thereby, creating an

analog controlled PWM.

18.10 Analog Input Connection

Considerations

A simplified circuit for an analog input is shown in

Figure 18-4. Since the analog input pins share their

connection with a digital input, they have reverse

biased ESD protection 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 for-

ward biased and a latch-up may occur.

A maximum source impedance of 10 k

 is recommended

for the analog sources. Also, any external component

connected to an analog input pin, such as a capacitor or

a Zener diode, should have very little leakage current to

minimize inaccuracies introduced.

FIGURE 18-4:

ANALOG INPUT MODEL

Note:

To use CxIN+ and CxINx- pins as analog

input, the appropriate bits must be set in

the ANSEL register and the corresponding

TRIS bits must also be set to disable the

output drivers.

Note 1: When reading a PORT register, all pins

configured as analog inputs will read as a

‘0’. Pins configured as digital inputs will

convert as an analog input, 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.

Rs < 10K

CPIN

5 pF

VDD

 0.6V

RIC

ILEAKAGE(1)

Vss

Legend: CPIN

= Input Capacitance

ILEAKAGE = Leakage Current at the pin due to various junctions

RIC

= Interconnect Resistance

= Source Impedance

= Analog Voltage

= Threshold Voltage

To Comparator

Note 1: See Section 29.0 “Electrical Specifications”.

Analog

Input

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