PIC16F1825T-ESS datasheet(178/448 Pages) MICROCHIP

178 / 448 page

PIC16(L)F1825/1829

DS41440C-page 178

 2010-2012 Microchip Technology Inc.

19.9

Interaction with ECCP Logic

In some devices, a comparator output signal can be

used to trigger the auto-shutdown feature found within

the ECCP module. When the ECCP auto-shutdown

feature is enabled and a comparator output signal is

selected as the source, the comparator can be used

simultaneously as a general purpose comparator and

as the ECCP auto-shutdown source. In addition, the

comparator output signal can also be routed to the

designated I/O pin. If the ECCP Auto-Restart mode is

also enabled, the comparators can be used as a

closed loop analog feedback circuit to the ECCP,

thereby creating an analog controlled PWM.

Please see section Section 24.4.3 “Enhanced PWM

Auto-shutdown mode”

for more information.

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

forward 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 19-3:

ANALOG INPUT MODEL

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.

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 30.0 “Electrical Specifications”.

Analog

Input

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