Datasheet

305
ATmega16U4/32U4 [DATASHEET]
Atmel-7766J-USB-ATmega16U4/32U4-Datasheet_04/2016
Thanks to these four values and the linear characteristics of the temperature sensor and Internal RC Oscillator,
firmware can easily recalibrate the RC Oscillator on-the-go in function of the temperature sensor measure
(3)
(an
application note describes the operation):
Figure 24-8. Linear Characterization of OSCCAL in Function of T° Measurement from ADC
Notes: 1. The temperature sensor calibration values cannot be used to do accurate temperature measurements since
the calibration temperature during production is not accurate (±10°C)
2. Be aware that if EESAVE fuse is left unprogrammed, any chip erase operation will clear the temperature
sensor calibration values contained in EEPROM memory.
3. Accuracy results after a software recalibration of OSCCAL in function of Temperature is given by
characterization.
24.7 ADC Noise Canceler
The ADC features a noise canceler that enables conversion during sleep mode to reduce noise induced from
the CPU core and other I/O peripherals. The noise canceler can be used with ADC Noise Reduction and Idle
mode. To make use of this feature, the following procedure should be used:
a. Make sure that the ADC is enabled and is not busy converting. Single Conversion mode must be
selected and the ADC conversion complete interrupt must be enabled.
5. Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the CPU
has been halted.
6. If no other interrupts occur before the ADC conversion completes, the ADC interrupt will wake up
the CPU and execute the ADC Conversion Complete interrupt routine. If another interrupt wakes up
the CPU before the ADC conversion is complete, that interrupt will be executed, and an ADC
Conversion Complete interrupt request will be generated when the ADC conversion completes. The
CPU will remain in active mode until a new sleep command is executed.
Note that the ADC will not be automatically turned off when entering other sleep modes than Idle mode and
ADC Noise Reduction mode. The user is advised to write zero to ADEN before entering such sleep modes to
avoid excessive power consumption.
If the ADC is enabled in such sleep modes and the user wants to perform differential conversions, the user is
advised to switch the ADC off and on after waking up from sleep to prompt an extended conversion to get a
valid result.
24.7.1 Analog Input Circuitry
The analog input circuitry for single ended channels is illustrated in Figure 24-9. An analog source applied to
ADCn is subjected to the pin capacitance and input leakage of that pin, regardless of whether that channel is
selected as input for the ADC. When the channel is selected, the source must drive the S/H capacitor through
the series resistance (combined resistance in the input path).
OSCCAL
T(ADC
O1
O2
T1
T2