ATmega48P Atmel Corporation, ATmega48P Datasheet - Page 255
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ATmega48P
Manufacturer Part Number
ATmega48P
Description
Manufacturer
Atmel Corporation
Specifications of ATmega48P
Flash (kbytes)
4 Kbytes
Pin Count
32
Max. Operating Frequency
20 MHz
Cpu
8-bit AVR
# Of Touch Channels
12
Hardware Qtouch Acquisition
No
Max I/o Pins
23
Ext Interrupts
24
Usb Speed
No
Usb Interface
No
Spi
2
Twi (i2c)
1
Uart
1
Graphic Lcd
No
Video Decoder
No
Camera Interface
No
Adc Channels
8
Adc Resolution (bits)
10
Adc Speed (ksps)
15
Analog Comparators
1
Resistive Touch Screen
No
Temp. Sensor
Yes
Crypto Engine
No
Sram (kbytes)
0.5
Eeprom (bytes)
256
Self Program Memory
NO
Dram Memory
No
Nand Interface
No
Picopower
Yes
Temp. Range (deg C)
-40 to 85
I/o Supply Class
1.8 to 5.5
Operating Voltage (vcc)
1.8 to 5.5
Fpu
No
Mpu / Mmu
no / no
Timers
3
Output Compare Channels
6
Input Capture Channels
1
Pwm Channels
6
32khz Rtc
Yes
Calibrated Rc Oscillator
Yes
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24.6.1
24.6.2
8025M–AVR–6/11
Analog Input Circuitry
Analog Noise Canceling Techniques
The analog input circuitry for single ended channels is illustrated in Figure 24-8. An analog
source applied to ADCn is subjected to the pin capacitance and input leakage of that pin, regard-
less 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).
The ADC is optimized for analog signals with an output impedance of approximately 10 kΩ or
less. If such a source is used, the sampling time will be negligible. If a source with higher imped-
ance 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.
Signal components higher than the Nyquist frequency (f
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.
Figure 24-8. Analog Input Circuitry
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:
a. Keep analog signal paths as short as possible. Make sure analog tracks run over the
b. The AV
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
analog ground plane, and keep them well away from high-speed switching digital
tracks.
an LC network as shown in
switch while a conversion is in progress. However, using the 2-wire Interface (ADC4
ADCn
CC
pin on the device should be connected to the digital V
I
IH
I
Figure
IL
24-9.
1..100 kΩ
ATmega48P/88P/168P
ADC
/2) should not be present for either
C
S/H
= 14 pF
CC
supply voltage via
V
CC
/2
255