259
4317I–AVR–01/08
AT90PWM2/3/2B/3B
22. Digital to Analog Converter - DAC
22.1
Features
•
10 bits resolution
•
8 bits linearity
•
+/- 0.5 LSB accuracy between 150mV and AVcc-150mV
•
Vout = DAC*Vref/1023
•
The DAC could be connected to the negative inputs of the analog comparators and/or to a
dedicated output driver.
•
Output impedance around 100 Ohm.
The AT90PWM2/2B/3/3B features a 10-bit Digital to Analog Converter. This DAC can be used
for the analog comparators and/or can be output on the D2A pin of the microcontroller via a ded-
icated driver.
This allows to drive (worst case) a 1nF capacitance in parallel with a resistor higher than 33K
load with a time constant around 1us. Response time and power consumption are improved by
reducing the load (reducing the capacitor value and increasing the load resistor value (The best
case is a high impedance)).
The DAC has a separate analog supply voltage pin, AV
CC
. AV
CC
must not differ more than ±
0.3V from V
CC
. See the paragraph
“ADC Noise Canceler” on page 241
on how to connect this
pin.
The reference voltage is the same as the one used for the ADC,
. These nominally 2.56V Vref or AV
CC
are provided On-chip. The volt-
age reference may be externally decoupled at the AREF pin by a capacitor for better noise
performance.