ATXMEGA256A3_1012 Datasheet, PDF (107/134 Pages) ATMEL Corporation – 8/16-bit XMEGA A3 Microcontroller

36.1.3 rev. A
8068T–AVR–12/10
XMEGA A3
• Bandgap voltage input for the ACs cannot be changed when used for both ACs simultaneously
• ADC gain stage output range is limited to 2.4V
• Sampled BOD in Active mode will cause noise when bandgap is used as reference
• Flash Power Reduction Mode can not be enabled when entering sleep mode
• JTAG enable does not override Analog Comparator B output
• Bandgap measurement with the ADC is non-functional when V_CC is below 2.7V
• DAC refresh may be blocked in S/H mode
• BOD will be enabled after any reset
• Both DFLLs and both oscillators has to be enabled for one to work
• Operating frequency and voltage limitations
• Inverted I/O enable does not affect Analog Comparator Output
1. Bandgap voltage input for the ACs cannot be changed when used for both ACs
simultaneously
If the bandgap voltage is selected as input for one Analog Comparator (AC) and then
selected/deselected as input for the another AC, the first comparator will be affected for up
to 1 us and could potentially give a wrong comparison result.
Problem fix/Workaround
If the Bandgap is required for both ACs simultaneously, configure the input selection for both
ACs before enabling any of them.
2. ADC gain stage output range is limited to 2.4 V
The amplified output of the ADC gain stage will never go above 2.4 V, hence the differential
input will only give correct output when below 2.4 V/gain. For the available gain settings, this
gives a differential input range of:
– 1x gain:
– 2x gain:
– 4x gain:
– 8x gain:
– 16x gain:
– 32x gain:
– 64x gain:
2.4 V
1.2 V
0.6 V
300 mV
150 mV
75 mV
38 mV
Problem fix/Workaround
Keep the amplified voltage output from the ADC gain stage below 2.4 V in order to get a cor-
rect result, or keep ADC voltage reference below 2.4 V.
3. Sampled BOD in Active mode will cause noise when bandgap is used as reference
Using the BOD in sampled mode when the device is running in Active or Idle mode will add
noise on the bandgap reference for ADC, DAC and Analog Comparator.
Problem fix/Workaround
If the bandgap is used as reference for either the ADC, DAC and Analog Comparator, the
BOD must not be set in sampled mode.
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