ATMEGA406_14 Datasheet, PDF (252/263 Pages) ATMEL Corporation – High Performance, Low Power AVR

3. Voltage Reference Spike
The Voltage Reference, VREF, will spike each time a temperature measurement is started
with the Voltage-ADC.
Problem Fix/Workaround
An accurate temperature measurement could be obtained by doing 10 temperature conver-
sions immediately after each other. The first 9 results would be inaccurate, but the 10th
conversion will be correct.
Figure 36-6 illustrates the spike on the Voltage Reference when doing 10 temperature con-
versions in a row (external decoupling capacitor of 1F).
Figure 36-6. Voltage Reference Spike
Voltage
1.1 V
V~50mV
VREF
t ~< 5ms
VADSC
VADMUX3:0 XXX
(10 VTEMP conversion in a row)
VTEMP
time
If the CC-ADC is doing current accumulation while the V-ADC is doing temperature mea-
surement, both the Instantaneous and the Accumulated conversion results will be affected.
The spike on VREF will be visible on 1 Accumulated Current (CADAC3…0) and 2 Instanta-
neous Current (CADIC1…0) conversion results.
252 ATmega406
2548F–AVR–03/2013