ATtiny261 Atmel Corporation, ATtiny261 Datasheet - Page 150

• Manufacturer Part Number: ATtiny261
• Manufacturer: Atmel Corporation

Specifications of ATtiny261

• Flash (kbytes): 2 Kbytes
• Pin Count: 20
• Max. Operating Frequency: 20 MHz
• Cpu: 8-bit AVR
• # Of Touch Channels: 4
• Hardware Qtouch Acquisition: No
• Max I/o Pins: 16
• Ext Interrupts: 16
• Usb Speed: No
• Usb Interface: No
• Spi: 1
• Twi (i2c): 1
• Graphic Lcd: No
• Video Decoder: No
• Camera Interface: No
• Adc Channels: 11
• Adc Resolution (bits): 10
• Adc Speed (ksps): 15
• Analog Comparators: 1
• Resistive Touch Screen: No
• Temp. Sensor: Yes
• Crypto Engine: No
• Sram (kbytes): 0.12
• Eeprom (bytes): 128
• Self Program Memory: YES
• Dram Memory: No
• Nand Interface: No
• Picopower: No
• 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: 2
• Output Compare Channels: 6
• Input Capture Channels: 1
• Pwm Channels: 6
• 32khz Rtc: No
• Calibrated Rc Oscillator: Yes

15.8
15.9
150
Analog Input Circuitry
Noise Canceling Techniques
ATtiny261/461/861
The analog input circuitry for single ended channels is illustrated in
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).
Figure 15-8. Analog Input Circuitry
The capacitor in
and any stray or parasitic capacitance inside the device. The value given is worst case.
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 impedant 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
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.
Digital circuitry inside and outside the device generates EMI which might affect the accuracy of
analog measurements. When conversion accuracy is critical, the noise level can be reduced by
applying the following techniques:
Where high ADC accuracy is required it is recommended to use ADC Noise Reduction Mode, as
described in
is above 1 MHz, or when the ADC is used for reading the internal temperature sensor, as
• Keep analog signal paths as short as possible.
• Make sure analog tracks run over the analog ground plane.
• Keep analog tracks well away from high-speed switching digital tracks.
• If any port pin is used as a digital output, it mustn’t switch while a conversion is in progress.
• Place bypass capacitors as close to V
ADCn
Section 15.7 on page
Figure 15-8
depicts the total capacitance, including the sample/hold capacitor
I
IH
149. This is especially the case when system clock frequency
I
IL
CC
and GND pins as possible.
1..100 kΩ
ADC
/2) should not be present to avoid
C
S/H
= 14 pF
Figure 15-8
V
CC
/2
2588E–AVR–08/10
An analog