Microchip Technology MA160014 データシート

 2010-2012 Microchip Technology Inc.

DS41412F-page 345

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  V

REF

 pins

• V

DD

 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.

The DAC has 32 voltage level ranges. The 32 levels
are set with the DACR<4:0> bits of the VREFCON2
register.

The DAC output voltage is determined by the following
equations:

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 be found in 

.

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, (V

SRC

+), or the

negative voltage source, (V

SRC

-) 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.

The DAC output voltage can be set to V

SRC

+ with the

least amount of power consumption by performing the
following:

• Clearing the DACEN bit in the VREFCON1 

register.

• Setting the DACLPS bit in the VREFCON1 

register.

• 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 

 for more information.

The DAC output voltage can be set to V

SRC

- with the

least amount of power consumption by performing the
following:

• Clearing the DACEN bit in the VREFCON1 

register.

• Clearing the DACLPS bit in the VREFCON1 

register.

• 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.

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. 

 shows

an example buffering technique.

V

OUT

V

SRC

+ V

SRC

-

–



 DACR<4:0>

25

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











=

+ V

SRC

-

V

SRC

+  =  V

DD

, V

REF

+ or FVR1

V

SRC

-  =  V

SS

 or V

REF

-