PIC16F688_09 datasheet(57/204 Pages) MICROCHIP

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DS41203E-page 55

PIC16F688

7.1.1

ANALOG INPUT CONNECTION

CONSIDERATIONS

A simplified circuit for an analog input is shown in

Figure 7-4. 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

forward biased and a latch-up may occur.

A maximum source impedance of 10 k

Ω 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 7-4:

ANALOG INPUT MODEL

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

±500 nA

Vss

AIN

Legend: CPIN

= Input Capacitance

ILEAKAGE = Leakage Current at the pin due to various junctions

RIC

= Interconnect Resistance

= Source Impedance

= Analog Voltage

= Threshold Voltage

To ADC Input

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