PIC12F1822-ISLASHMF datasheet(147/398 Pages) MICROCHIP

147 / 398 page

 2010 Microchip Technology Inc.

Preliminary

DS41413A-page 147

PIC12F/LF1822/16F/LF1823

16.0 DIGITAL-TO-ANALOG

CONVERTER (DAC) MODULE

The Digital-to-Analog Converter supplies a variable

voltage reference, ratiometric with the input source,

with 32 selectable output levels.

The input of the DAC can be connected to:

•External VREF pins

•VDD supply voltage

• FVR (Fixed Voltage Reference)

The output of the DAC can be configured to supply a

reference voltage to the following:

• Comparator positive input

• ADC input channel

•DACOUT pin

The Digital-to-Analog Converter (DAC) can be enabled

by setting the DACEN bit of the DACCON0 register.

16.1

Output Voltage Selection

The DAC has 32 voltage level ranges. The 32 levels

are set with the DACR<4:0> bits of the DACCON1

The DAC output voltage is determined by the following

equations:

EQUATION 16-1:

DAC OUTPUT VOLTAGE

16.2

Ratiometric Output Level

The DAC output value is derived using a resistor ladder

with each end of the ladder tied to a positive and

negative voltage reference input source. If the voltage

of either input source fluctuates, a similar fluctuation will

result in the DAC output value.

The value of the individual resistors within the ladder

can

found

Section 29.0

“Electrical

Specifications”.

16.3

Low-Power Voltage State

In order for the DAC module to consume the least

amount of power, one of the two voltage reference input

sources to the resistor ladder must be disconnected.

Either the positive voltage source, (VSRC+), or the

negative voltage source, (VSRC-) can be disabled.

The negative voltage source is disabled by setting the

DACLPS bit in the DACCON0 register. Clearing the

DACLPS bit in the DACCON0 register disables the

positive voltage source.

16.3.1

OUTPUT CLAMPED TO POSITIVE

VOLTAGE SOURCE

The DAC output voltage can be set to VSRC+ with the

least amount of power consumption by performing the

following:

• Clearing the DACEN bit in the DACCON0 register.

• Setting the DACLPS bit in the DACCON0 register.

• Configuring the DACPSS bits to the proper

positive source.

• Configuring the DACR<4:0> bits to ‘11111’ in the

DACCON1 register.

This is also the method used to output the voltage level

from the FVR to an output pin. See Section 16.4 “DAC

Voltage Reference Output” for more information.

Reference Figure 16-1 for output clamping examples.

16.3.2

OUTPUT CLAMPED TO NEGATIVE

VOLTAGE SOURCE

The DAC output voltage can be set to VSRC- with the

least amount of power consumption by performing the

following:

• Clearing the DACEN bit in the DACCON0 register.

• Clearing the DACLPS bit in the DACCON0 register.

• Configuring the DACNSS bits to the proper

negative source.

• Configuring the DACR<4:0> bits to ‘00000’ in the

DACCON1 register.

This allows the comparator to detect a zero-crossing

while not consuming additional current through the DAC

module.

Reference Figure 16-1 for output clamping examples.

VOUT

VSOURCE+VSOURCE-

–

 DACR<4:0>

-------------------------------







+ VSRC-

Note:

VSOURCE+ can equal FVR Buffer 2, VDD or

VREF+. VSOURCE- can equal VSS or VREF-.

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