Datasheet

 2009 Microchip Technology Inc. Preliminary DS41364D-page 169
PIC16F193X/LF193X
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 V
REF 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
register.
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 be found in 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, (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 DACCON0 register. Clearing the
DACLPS bit in the DACCON0 register disables the
positive voltage source.
16.4 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 DACCON0 register.
• Setting the DACLPS bit in the DACCON0 register.
• Configuring the DACPSS bits to the proper
positive source.
• Configuring the DACRx 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 16.6 “DAC
Voltage Reference Output” for more information.
16.5 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 DACCON0 register.
• Clearing the DACLPS bit in the DACCON0 register.
• Configuring the DACPSS bits to the proper
negative source.
• Configuring the DACRx 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.
16.6 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 16-2 shows
an example buffering technique.
VOUT VSRC+VSRC-–
DACR<4:0>
2
5
-------------------------------


=
+ V
SRC-
V
SRC+ = VDD, VREF+ or FVR1
V
SRC- = VSS or VREF-