Microchip Technology ARD00385 Data Sheet

DS39957D-page 392

 2009-2011 Microchip Technology Inc.

A single comparator is shown in 

, along with

the relationship between the analog input levels and
the digital output. When the analog input at V

IN

+ is less

than the analog input, V

IN

-, the output of the compara-

tor is a digital low level. When the analog input at V

IN

+

is greater than the analog input, V

IN

-, the output of the

comparator is a digital high level. The shaded areas of
the output of the comparator, in 

, represent

the uncertainty due to input offsets and response time.

Response time is the minimum time, after selecting a
new reference voltage or input source, before the com-
parator 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

A simplified circuit for an analog input is shown in

. Since the analog pins are connected to a

digital output, they have reverse biased diodes to V

DD

and V

SS

. The analog input, therefore, must be between

V

SS

 and V

DD

. 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.

Output

V

IN

-

V

IN

+

–

+

V

IN

+

V

IN

-

Output

VA

R

S

A

IN

C

PIN

5 pF

V

DD

V

T

 = 0.6V

V

T

 = 0.6V

R

IC

I

LEAKAGE

±100 nA

V

SS

C

PIN

= 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

<10k

