41594B datasheet(153/372 Pages) MICROCHIP

153 / 372 page

 2011-2012 Microchip Technology Inc.

Preliminary

DS41594B-page 153

PIC12LF1840T48A

19.7

Comparator Negative Input

Selection

The C1NCH bit of the CM1CON1 register directs one

of two analog pins to the comparator inverting input.

19.8

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 31.0 “Electrical Specifi-

cations” for more details.

19.9

Interaction with ECCP Logic

The C1 comparator can be used as a general purpose

comparator. The output can be brought out to the

C1OUT pin. When the ECCP auto-shutdown is active

it can use the comparator signal. If auto-restart is also

enabled, the comparator can be configured as a

closed loop analog feedback to the ECCP, thereby,

creating an analog controlled PWM.

19.10 Analog Input Connection

Considerations

A simplified circuit for an analog input is shown in

Figure 19-3. 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.

Note:

To use C1IN+ and C1INx- pins as analog

input, the appropriate bits must be set in

the ANSEL register and the correspond-

ing TRIS bits must also be set to disable

the output drivers.

Note:

When the comparator module is first

initialized, the output state is unknown.

Upon initialization, the user should verify

the output state of the comparator prior to

relying on the result, primarily when using

the result in connection with other

peripheral features, such as the ECCP

Auto-Shutdown mode.

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.

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