ATxmega256A3 Atmel Corporation, ATxmega256A3 Datasheet - Page 319

• Manufacturer Part Number: ATxmega256A3
• Manufacturer: Atmel Corporation

Specifications of ATxmega256A3

• Flash (kbytes): 256 Kbytes
• Pin Count: 64
• Max. Operating Frequency: 32 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 16
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 50
• Ext Interrupts: 50
• Usb Speed: No
• Usb Interface: No
• Spi: 10
• Twi (i2c): 2
• Uart: 7
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 16
• Adc Resolution (bits): 12
• Adc Speed (ksps): 2000
• Analog Comparators: 4
• Resistive Touch Screen: No
• Dac Channels: 2
• Dac Resolution (bits): 12
• Temp. Sensor: Yes
• Crypto Engine: AES/DES
• Sram (kbytes): 16
• Eeprom (bytes): 4096
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: Yes
• Temp. Range (deg C): -40 to 85
• I/o Supply Class: 1.6 to 3.6
• Operating Voltage (vcc): 1.6 to 3.6
• Fpu: No
• Mpu / Mmu: no / no
• Timers: 7
• Output Compare Channels: 22
• Input Capture Channels: 22
• Pwm Channels: 22
• 32khz Rtc: Yes
• Calibrated Rc Oscillator: Yes

26.6
26.7
26.8
26.9
8077H–AVR–12/09
DAC clock
Timing constraints
Low Power mode
Calibration
Figure 26-2. DAC output model
Notes:
The DAC is clocked from the Peripheral clock (clk
refresh rate in S/H mode is configured relative to the Peripheral Clock.
Some timing constraints are given to make sure the DAC operates correctly. The timing con-
straints are relative to the frequency of the Peripheral clock. Not meeting the timing constraints
may reduce the accuracy of DAC conversions.
To reduce the power consumption in DAC conversions, the DAC may be set in a Low Power
mode. In Low Power mode, the DAC is turned off between each conversion. Conversion time
will be longer if new conversions are started in this mode. To put the DAC into low power mode,
you need to set the bit 1 in CTRLA register (called DACCRA).
To achieve optimal accuracy, it is possible to calibrate both gain and offset error in the DAC.
There is a 7-bit calibration value for gain adjustment and a 7-bit calibration value for offset
adjustment.
To get the best calibration result it is recommended to use the same VREF, output channel
selection, sampling time, and refresh interval when calibrating as will be used in normal DAC
operation. The theoretical transfer function for the DAC was shown in
Including errors, the DAC output value can be expressed as:
In an ideal DAC, gain is 1 and offset is 0.
V
• The DAC sampling time is the time interval between a completed channel conversion until
• The DAC refresh time is the time interval between each time a channel is updated in dual
DAC voltage
DACxX
starting a new conversion. This should not be less than 1 µs for single channel mode and 1.5
µs for dual channel (S/H) mode.
channel mode. This should not be more than 30 µs.
1. The DAC R
2. The DAC R
=
gain
⋅
CHnDATA
--------------------------- -
0xFFF
channel
channel
Buffer
+
is ~300 Ω for ATxmegaA3 and ATxmegaA4
is ~850 Ω for ATxmegaA1
offset
DAC out
PER
) directly. The DAC conversion interval and
R
R
feedback
channel
”Overview” on page
XMEGA A
DAC output
317.
319