ATtiny5 datasheet(89/168 Pages) ATMEL

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8127C–AVR–10/09

ATtiny4/5/9/10

• 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.

• Enter ADC Noise Reduction mode (or Idle mode). The ADC will start a conversion once the

CPU has been halted.

• 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 enter-

ing such sleep modes to avoid excessive power consumption.

13.8 Analog Input Circuitry

The analog input circuitry for single ended channels is illustrated in Figure 13-8 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 (sample and hold) capacitor through the series resistance (combined

resistance in the input path).

Figure 13-8. Analog Input Circuitry

The capacitor in Figure 13-8 depicts the total capacitance, including the sample/hold capacitor

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 k

Ω, or

less. With such sources, 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. This 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 (fADC/2) should not be present 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.

ADCn

IIH

1..100 k

ohm

CS/H= 14 pF

VCC/2

IIL

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