Atmel ATmega328P Xplained Mini MEGA328P-XMINI MEGA328P-XMINI Data Sheet
Product codes
MEGA328P-XMINI
245
ATmega48A/PA/88A/PA/168A/PA/328/P [DATASHEET]
Atmel-8271H-AVR- ATmega-Datasheet_08/2014
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).
the series resistance (combined resistance in the input path).
The ADC is optimized for analog signals with an output impedance of approximately 10 k
or less. If such a
source is used, the sampling time will be negligible. If a source with higher impedance is used, the sampling
time will depend on how long time the source needs to charge the S/H capacitor, with can vary widely. The user
is recommended to only use low impedance sources with slowly varying signals, since this minimizes the
required charge transfer to the S/H capacitor.
time will depend on how long time the source needs to charge the S/H capacitor, with can vary widely. The user
is recommended to only use low impedance sources with slowly varying signals, since this minimizes the
required charge transfer to the S/H capacitor.
Signal components higher than the Nyquist frequency (f
ADC
/2) should not be present for either kind of channels,
to avoid distortion from unpredictable signal convolution. The user is advised to remove high frequency
components with a low-pass filter before applying the signals as inputs to the ADC.
components with a low-pass filter before applying the signals as inputs to the ADC.
Figure 24-8.
Analog Input Circuitry
24.6.2 Analog Noise Canceling Techniques
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of analog
measurements. If conversion accuracy is critical, the noise level can be reduced by applying the following
techniques:
measurements. If conversion accuracy is critical, the noise level can be reduced by applying the following
techniques:
a.
Keep analog signal paths as short as possible. Make sure analog tracks run over the analog ground
plane, and keep them well away from high-speed switching digital tracks.
plane, and keep them well away from high-speed switching digital tracks.
b.
The AV
CC
pin on the device should be connected to the digital V
CC
supply voltage via an LC network as
.
c.
Use the ADC noise canceler function to reduce induced noise from the CPU.
d.
If any ADC [3:0] port pins are used as digital outputs, it is essential that these do not switch while a
conversion is in progress. However, using the 2-wire Interface (ADC4 and ADC5) will only affect the
conversion on ADC4 and ADC5 and not the other ADC channels.
conversion is in progress. However, using the 2-wire Interface (ADC4 and ADC5) will only affect the
conversion on ADC4 and ADC5 and not the other ADC channels.
ADCn
I
IH
1..100 k
Ω
C
S/H
= 14 pF
V
CC
/2
I
IL