PIC18F45J50-I/SOSQTP 데이터 시트보기 (PDF) - Microchip Technology

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PIC18F45J50-I/SOSQTP

28/44-Pin, Low-Power, High-Performance USB Microcontrollers with nanoWatt XLP Technology

Microchip Technology 

PIC18F46J50 FAMILY

23.2 Comparator Operation

A single comparator is shown in Figure 23-2, 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 compara-

tor 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 23-2 represent

the uncertainty due to input offsets and response time.

FIGURE 23-2:

SINGLE COMPARATOR

VIN+

+

VIN-

–

Output

VIN-

VIN+

Output

23.3 Comparator Response Time

Response time is the minimum time, after selecting a

new reference voltage or input source, before the

comparator output has a valid level. 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 to

a comparator input change. Otherwise, the maximum

delay of the comparators should be used (see

Section 30.0 “Electrical Characteristics”).

23.4 Analog Input Connection

Considerations

Figure 23-3 provides a simplified circuit for an analog

input. 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 is recommended

for the analog sources. Any external component con-

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

Zener diode, should have very little leakage current.

FIGURE 23-3:

COMPARATOR ANALOG INPUT MODEL

VDD

RS < 10k

AIN

VA

CPIN

5 pF

VT = 0.6V

VT = 0.6V

RIC

ILEAKAGE

±100 nA

Comparator

Input

VSS

Legend:

CPIN

=

VT

=

ILEAKAGE =

RIC

=

RS

=

VA

=

Input Capacitance

Threshold Voltage

Leakage Current at the pin due to various junctions

Interconnect Resistance

Source Impedance

Analog Voltage

 2011 Microchip Technology Inc.

DS39931D-page 387

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