16F1825 datasheet(165/420 Pages) MICROCHIP

165 / 420 page

 2010 Microchip Technology Inc.

Preliminary

DS41440A-page 165

PIC16F/LF1825/1829

17.0 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.

17.1

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 17-1:

DAC OUTPUT VOLTAGE

17.2

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 30.0

“Electrical

Specifications”.

17.3

DAC Voltage Reference Output

The DAC can be output to the DACOUT pin by setting

the DACOE bit of the DACCON0 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 17.5 shows

an example buffering technique.

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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