PIC18F23K22-ESLASHML datasheet(339/496 Pages) MICROCHIP

339 / 496 page

 2010 Microchip Technology Inc.

Preliminary

DS41412C-page 339

PIC18(L)F2X/4XK22

22.0 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 VREFCON1 register.

22.1

Output Voltage Selection

The DAC has 32 voltage level ranges. The 32 levels

are set with the DACR<4:0> bits of the VREFCON2

The DAC output voltage is determined by the following

equations:

EQUATION 22-1:

DAC OUTPUT VOLTAGE

22.2

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 27.0

“Electrical

Characteristics”.

22.3

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 VREFCON1 register. Clearing the

DACLPS bit in the VREFCON1 register disables the

positive voltage source.

22.4

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 VREFCON1

• Setting the DACLPS bit in the VREFCON1

• Configuring the DACPSS bits to the proper

positive source.

• Configuring the DACRx bits to ‘11111’ in the

VREFCON2 register.

This is also the method used to output the voltage level

from the FVR to an output pin. See Section 22.6 “DAC

Voltage Reference Output” for more information.

22.5

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 VREFCON1

• Clearing the DACLPS bit in the VREFCON1

• Configuring the DACPSS bits to the proper

negative source.

• Configuring the DACRx bits to ‘00000’ in the

VREFCON2 register.

This allows the comparator to detect a zero-crossing

while not consuming additional current through the DAC

module.

22.6

DAC Voltage Reference Output

The DAC can be output to the DACOUT pin by setting

the DACOE bit of the VREFCON1 register to ‘1’.

Selecting the DAC reference voltage for output on the

DACOUT pin automatically overrides the digital output

buffer and digital input threshold detector functions of

that pin. Reading the DACOUT pin when it has been

configured for DAC reference voltage output will always

return a ‘0’.

Due to the limited current drive capability, a buffer must

be used on the DAC voltage reference output for

external connections to DACOUT. Figure 22-2 shows

an example buffering technique.

VOUT

VSRC+VSRC-

–

 DACR<4:0>

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







+ VSRC-

VSRC+ = VDD, VREF+ or FVR1

VSRC- = VSS or VREF-

PIC18F23K22-E/ML Datasheet(PDF) 339 Page - Microchip Technology

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